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Arthrobacter
Arthrobacter M Gobbetti and CG Rizzello, University of Bari, Bari, Italy Ó 2014 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by Marco Gobbetti, Emanuele Smacchi, volume 1, pp 54–61, Ó 1999, Elsevier Ltd.
General Characteristics
Ecology
Arthrobacter is a genus of mainly soil bacteria whose major distinguishing feature is a rod–coccus growth cycle. Irregular rods in young cultures are replaced by stationary-phase coccoid cells, which when transferred to fresh medium, produce outgrowths to give irregular rods again. Coccoid cells may assume large and morphologically aberrant forms when in conditions of severe nutritional stress. Both rod and coccoid forms are Gram-positive but easily may be decolorized. Gramnegativity may appear in midexponential- to stationary-phase cells. Cells do not form endospores; they are nonmotile or motile by one subpolar or a few lateral flagella, obligate aerobes, and catalase positive. Their metabolism is respiratory, never fermentative (little or no acid is formed from sugars), and the nutrition is nonexacting. The G þ C content of the DNA is in the range of 59–66 mol% (actinomycete branch) and the cell wall peptidoglycan contains lysine as diamino acid. A total of 15 species of Arthrobacter (sensu stricto) were reported in the Bergey’s Manual of Systematic Bacteriology until 2000, whereas about 70 species now are recognized (Euzéby: list of prokaryotic names with standing in nomenclature – Genus Arthrobacter) Two groups of species, Arthrobacter globiformis/Arthrobacter citreus and Arthrobacter nicotianae/ Arthrobacter sulfureus, are accepted on the basis of DNA–DNA homology, 16S rRNA cataloging studies, peptidoglycan structure, teichoic acid content, and lipid composition (Table 1). On the basis of 16S rDNA studies, the separation of Arthrobacter into two groups of species has no phylogenetic validation. Members of the second group (e.g., A. nicotianae) are significantly more closely related to certain members of the first group (e.g., A. globiformis) than members of the first group are related to each other (e.g., A. globiformis vs. A. citreus). Nutritional versatility is characteristic: carbohydrates, organic acids, amino acids, aromatic compounds, and nucleic acids are used as carbon and energy sources. A comparison between some metabolic properties of A. globiformis and A. nicotianae is reported in Table 2. With the exception of biotin, vitamins or other organic growth factors are not required. Arthrobacters mainly use inorganic nitrogen. Arthrobacter citreus is a notable exception as it uses a more limited range of compounds as energy and carbon sources and requires complex growth factors in addition to a siderophore, such as ferrichrome or mycobactin, for growth. The optimum temperature for growth is 25–30 C, and most arthrobacters grow in the range of about 10–35 C. Many strains also grow at 5 C and a few grow at 37 C. Growth at 37 C is influenced by the culture medium. On a phylogenetic basis (homology within the 16S ribosomal gene), the Arthrobacter species could not be separated from members of the genus Micrococcus. Both are included in the class: Actinobacteria, Subclass V: Actinobacteridae, Order I: Actinomycetales, Suborder IX: Micrococcineae, Family I: Micrococcaceae (see Bergey’s Manual of Systematic Bacteriology, 2011).
Arthrobacters are numerically important among the indigenous bacterial biota of soils and rhizospheres. Nutritional versatility, extreme resistance to drying, and starvation ensure their predominance in soils of different geographic locations. Soil acidity decreases cell viability. Psychrotrophic strains are abundant in terrestrial subsurface environments and occur in the Arctic and Antarctic, glacier silts, alpine glacier cryoconites, and ice caves. Isolates have been found in oil brines raised from soil layers at w200–700 m depth. Arthrobacter spp. are relatively common on the aerial surface of plants, including flowers. Marine and freshwater fish and other seafoods contain arthrobacters. They occur in shark spoilage, eviscerated freshwater fish, fish-pen slime, and shrimp. Other populated habitats include sewage, brewery waste, wastewater reservoir sediments, deep poultry litter, dairy waste-activated sludge, and the surface of smear surfaceripened cheeses. Recently, different novel species have been isolated from archaeological mural paintings. Arthrobacter spp. were also isolated from human and veterinary clinical sources.
Encyclopedia of Food Microbiology, Volume 1
Culture Media Arthrobacter spp. normally are isolated from soil by plating on nonselective media because they are an appreciable proportion of the aerobic, cultivable population. Soil extract agar is used largely because it is sufficiently poor in carbon and energy sources. Possible modifications could include the addition of low concentrations of yeast extract and glucose to give higher counts, the incorporation of nystatin and cycloheximide to suppress fungi growth, and salt to reduce growth of Gramnegative bacteria. The isolation of arthrobacters in selective medium (Table 3) gives counts several times higher than those on nutritionally poor medium. The combination of 0.01% cycloheximide and 2.0% NaCl is effective in inhibiting fungi and most Streptomyces spp., Nocardia spp., and Gram-negative bacteria. Methyl red (150 mg ml1) inhibits other Gram-positive bacteria but does not affect arthrobacters.
Metabolism and Enzymes Carbohydrate dissimilation by Arthrobacter spp. falls into two groups. Arthrobacter globiformis, Arthrobacter ureafaciens, and Arthrobacter crystallopoietes primarily use the Embden– Meyerhof–Parnas and, to a lesser extent, the hexose monophosphate (HMP) pathways. Arthrobacter pascens and Arthrobacter atrocyaneus use the Entner–Doudoroff and HMP pathways. The pyruvate formed is oxidized by the tricarboxylic acid cycle, and the cytochrome system mediates the terminal
http://dx.doi.org/10.1016/B978-0-12-384730-0.00009-4
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70 Arthrobacter
Table 1
Characteristics of some Arthrobacter speciesa A. A. crystall- A. A. globiformis opoietes pascens ramosus
A. A. histidinoaurescens lovorans
A. ilicis
A. ureafaciens
A. A. atrocyaneus oxydans
A. citreus
A. nicotianae
A. protophormiae
A. A. uratoxydans sulfureus
Peptidoglycan type A3a variationb A4a variationb MK-9(H2)c MK-8c Teichoic acid Cell wall sugars
Lys-Ala
Lys-Ala
Lys-Ala
Lys-Ala
þ – þ – – Gal, Glu
þ – þ – – Gal, Glu
þ – þ – – Gal, Rha, Man
Lys-AlaThr-Ala þ – þ – – Gal, Glu
Lys-AlaThr-Ala þ – þ – – Gal, Rha, Man
Lys-AlaThr-Ala þ – þ – – Gal (Man)
Lys-Ser-Ala
þ – þ – – Gal, Glu
Lys-AlaThr-Ala þ – þ – – Gal (Man)
Lys-SerThr-Ala þ – þ – – Gal, Glu
Lys-ThrAla þ – þ – – Gal
Lys-AlaGlu – þ – þ þ ND
Lys-AlaGlu – þ – þ þ ND
DNA homologye Starch hydrolysis Motility
100%f
16%f
35%f
25%f
22%f
36%f
ND
31%f
24%f
50%f
18%f
Lys-AlaGlu – þ – þ þ Gal, Glc (one strain) 100%g
39%g
ND
– þ d d þ Gal, Glc (one strain) 22%g
þ
–
þ
–
þ
–
–
–
þ
þ
–
þ
–
–
–
–
–
–
þ
–
–
þ
–
þ
–
þ
–
–
þh
þh
Characteristics
þ – þ – – Gal, Glu (Man)
Lys-Glu
Symbols: þ, 90% or more of the strains are positive; , 90% or more of the strains are negative; (), conflicting reports on occurrence; ND, no data. Within the type A peptidoglycan (cross-linkage between positions 3 and 4 of the peptide subunits), two groups occur: A3a variations (the interpeptide bridge of peptidoglycan contains only monocarboxylic acids and/or glycine) and A4a variations (the interpeptide bridge always contains a dicarboxylic acid and in most strains also alanine). c MK-9(H2), dihydrogenated menaquinones with nine isoprene units as major components. MK-8, unsaturated menaquinones with eight isoprene units as major components. d A. sulfureus either contains MK-9 as the major menaquinone or comparable amounts of MK-9 and MK-10. e Homology index is expressed as percent of 3H-DNA bound to a certain disc DNA relative to the homologous reaction. f DNA homologies of named strains versus A. globiformis DSM 20125. g DNA homologies of named strains versus A. nicotianae DSM 20123. h A. uratoxydans, rods, motile by peritrichous flagella or nonmotile. A. sulfureus, rods motile by one or few lateral flagella or nonmotile. a
b
Arthrobacter Table 2 Comparison of some metabolic features between Arthrobacter globiformis DSM 20124 and Arthrobacter nicotianae DSM 20123a
Metabolic properties Utilization of 4-Aminobutyrate 5-Aminovalerate Malonate 4-Hydroxybenzoate Glyoxylate 2-Ketogluconate L Leucine L-Asparagine L-Arginine L-Histidine L-Xylose D-Ribose L-Arabinose D-Galactose L-Rhamnose D-Xylitol m-Inositol 2,3-Butylene glycol Glycerol Nicotine Hydrolysis of Xanthine Casein
A. globiformis DSM 20124
A. nicotianae DSM 20123
þ – þ þ þ þ – þ þ þ þ þ þ þ þ þ þ – þ –
þ þ þ þ – – þ þ – þ þ þ þ þ – – – þ þ þ
þ þ
– þ
a Symbols: þ, 90% or more of the strains are positive; , 90% or more of the strains are negative.
Table 3 Selective medium of Hagedorn and Holta for the isolation of Arthrobacter spp. Compound
Quantity
Trypticase soy agar Yeast extract NaCl Cycloheximide Methyl redb Agar
0.4% 0.2% 2.0% 0.01% 150 mg ml1 1.5%
a
Plate counts are made by spreading 0.1 ml amounts of suitable dilutions over the surface of sterile medium in Petri dishes. Peptone solution (0.5%, wt vol1) is used as the diluent. b The methyl red is filter sterilized and added aseptically to the autoclaved, cooled medium. The medium is adjusted to the pH of the particular soil being examined.
electron transport. When acetate is used as the carbon and energy source, arthrobacters must produce tricarboxylic acid cycle intermediates for biosynthetic purposes and should have mechanisms to produce acceptor molecules for C2 units. The glyoxylate cycle serves this purpose: Key enzymes of this cycle have been found in Arthrobacter spp. when grown on acetate plus glycine. Arthrobacter globiformis grows on glycine as the sole carbon and energy source and converts this amino acid through serine into pyruvate. Pyruvate is converted into C4 dicarboxylic acids for the tricarboxylic acid cycle and also into phosphoenolpyruvate, as a precursor of carbohydrates. Additionally,
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nucleic acids (both DNA and RNA) are decomposed to produce uric acid, allantoin, and urea. Arthrobacters from soil, but not from cheese and fish, use both uric acid and allantoin as the sole sources of carbon, energy, and nitrogen. Arthrobacters carry out heterotrophic nitrification. Cells must be provided with a carbon compound to produce energy and to synthesize the carbon-containing products of nitrification. Ammonium is converted into an amide, which is then oxidized to acetohydroxamic acid. The latter is converted rapidly by a reversible reaction into free hydroxylamine, but it is also oxidized slowly to nitrosoethanol. Nitrite and nitrate are late products in this sequence. Nitrite and nitrate are formed from aliphatic nitro-compounds. Arthrobacters isolated from soil respire nitrate in the presence of oxygen, but, in contrast to other soil bacteria, do not synthesize periplasmic-type nitrate reductase. Soil arthrobacters grown with excess glucose and a limited amount of NHþ 4 , HPO4 , or SO4 are particularly rich in storage polysaccharides such as glycogen. Glycogen enables survival for prolonged periods of nitrogen depletion and at the same time provides energy and intermediates for protein synthesis when inorganic nitrogen is available. Glycogen has an exceptionally high degree of branching. Extracellular polysaccharides are produced commonly by arthrobacters. Polysaccharides may consist of glucose, galactose, and uronic acid or mannuronic acid. Strains synthesize b-fructofuranosidase, which transfers the fructosyl residues of sucrose to aldoses or ketoses, to produce hetero-oligosaccharides. Such compounds protect against predation by protozoa in natural environments and never are used as a carbon and energy source by producers. The majority of Arthrobacter spp. isolated from soil, milk, cheese, and activated sludge are highly proteolytic. When actively growing in the soil, arthrobacters produce extracellular proteinases. Synthesis is repressed by high amino acid concentration. Enzymes are stable. The proteinase of A. ureafaciens consists of a single peptide chain of 221 amino acid residues cross-linked by two disulfide bridges, which, in part, explain its stability. Proteinases may have very high temperature optima, w70 C, and milk-clotting properties. Two extracellular serine proteinases with molecular masses of about 53–55 kDa and 70–72 kDa have been purified from A. nicotianae isolated from smear surface cheese. The enzymes differ with respect to temperature optimum (55–60 C and 37 C), tolerance to low values of pH and temperature, heat stability, sensitivity to ethylenediaminetetraacetic acid, and sulfhydryl blocking agents and hydrophobicity. Peptidases have been less studied than proteinases. An aminopeptidase of broad specificity, a proline iminopeptidase with activity against long peptides with a free N-terminal proline, and an imidodipeptidase (prolidase), which hydrolyzes only dipeptides, were found in cell extracts of soil Arthrobacter spp. Arthrobacters, especially those isolated from soil, have enzymes that enable them to degrade unusual and polymeric compounds. Strains that use levoglucosan (1,6-anhydro-b-Dglucopyranose) possess a levoglucosan dehydrogenase. Glucose is produced from levoglucosan by three steps: dehydrogenation, intramolecular hydrolysis, and nicotinamide adenine dinucleotide–dependent reduction. Levoglucosan dehydrogenase catalyzes the initial step. This pathway is
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Arthrobacter
distinct from those reported for soil yeasts and fungi. A levanase, which rapidly hydrolyzes levan (b-D-fructose polymer) in an endo-type manner to produce a series of levanoligosaccharides, was found. Pectolytic activity as well as the capacity to degrade another polyuronide such as alginic acid seems rather rare in arthrobacters. Methylamine oxidase, used to assimilate carbon in the form of methylamine or ethylamine, is synthesized by methylotroph Arthrobacter strains. It oxidizes primary amines methyl-, ethyl-, propyl-, butyl-, ethanol-, and benzylamine, but not tyramine, spermine, putracine, trimethylamine, and dimethylamine. Only O2 acts as a reoxidizing substrate for this enzyme. A maltooligosyl-trehalose synthase, which converts maltooligosaccharide into maltooligosyl trehalose by intramolecular transglycosylation, and a maltooligosyl-trehalose trehalohydrolase, which hydrolyzes the a-1,4-glucosidic bond between maltooligosyl and trehalose moieties, have been found in Arthrobacter spp., which accumulate trehalose. Arthrobacter globiformis produces an inulinase, which degrades inulin through an exo-type reaction. Choline oxidase has been found in A. pascens and A. globiformis. This is a cytosolic flavoprotein, hydrogen-peroxide-forming oxidase that oxidizes choline to produce glycine-betaine by a two-step reaction with betaine aldehyde as the intermediate. Betaine acts as a nontoxic osmolyte, highly compatible with metabolic functions at high cytoplasmic concentrations and contributes to turgor adjustment in cells subjected to osmotic stress.
Genetics and Bacteriophages Several genes of Arthrobacter spp. have been cloned and sequenced. The focus here is on genes for food enzymes. A 5.1 kbp genomic DNA fragment was cloned from trehalose-producing Arthrobacter sp. strain Q36. Sequence analysis revealed two open reading frames (ORFs) of 2325 and 1794 bp, encoding maltooligosyl-trehalose synthase and maltooligosyl-trehalose trehalohydrolase. A novel trehalose synthase gene (treS) from Arthrobacter aurescens CGMCC was cloned and expressed in Escherichia coli. Enzymes have several regions common to the a-amylase family. Some arthrobacters infrequently produce b-galactosidase when grown in lactose minimal media. The gene has similarities with the E. coli lacZ gene. When DNA was transformed into an E. coli host, three fragments each encoding a different b-galactosidase isoenzyme were obtained. The nucleotide sequence of the smallest fragment has no total similarity with the lacZ family but has regions similar to b-galactosidase isoenzymes from Bacillus stearothermophilus and Bacillus circulans. Different b-galactosidase genes were found in Arthrobacter sp. ON14 (galA and galB), Arthrobacter sp. 20B (bgaS), Arthrobacter sp. SB (bgaS3), and Arthrobacter psychrolactophilus F2 (bglA). The gene-encoding inulin fructotransferase was sequenced in A. globiformis S14-3 and Arthrobacter sp. H65-7. The two genes share only 49.8% homology and the sequence analysis of the ift gene from strain H65-7 consists of a single ORF of 1314 bp that encodes a signal peptide of 32 amino acids and a mature protein of 405 amino acids. The gene encoding an extracellular isomalto-dextranase (imd) was isolated from the chromosome of A. globiformis T6 and expressed in E. coli. A single ORF consisting of 1926 bp that encodes a polypeptide composed of a signal peptide of 39
amino acids and a mature protein of 602 amino acids was found. The primary structure has no significant homology with the structures of any other reported carbohydrases and the enzyme differs in that it is capable of hydrolyzing dextran by releasing only isomaltose units from dextran chains. Isomaltose inhibits the biosynthesis of mutan, which is the major component of dental plaque and may be of significant importance in the prevention of dental caries. A gene for dextranase (aodex) also was found in Arthrobacter oxydans; it was cloned and expressed in E. coli. The pcd plasmid gene for phenylcarbamate hydrolase was sequenced in A. oxydans P52. It has significant homology with esterases of eukaryotic origin. Arthrobacter globiformis M6 produces a nonreducing oligosaccharide from starch, characterized by a cyclic structure consisting of four glucose residues joined by alternate a-1,4 and a-1,6 linkages and designated cyclic maltosyl-maltose (CMM). The gene encoding for the glycosyl-transferase (cmmA), which is involved in the synthesis of CMM from starch, was identified. Cholesterol oxidases are a group of flavin adenine dinucleotide (FAD)-dependent enzymes having important industrial applications and are used widely to determine cholesterol in food and blood serum through peroxidase-coupled assays. In addition, they are used in the production of starting material for the chemical synthesis of pharmaceutical steroids. The gene (choAA) encoding cholesterol oxidase from Arthrobacter simplex F2 was cloned and expressed in E. coli. A host–vector system based on pULRS8 containing the kanamycin-resistant gene, kan (Tn5), was used for transforming Arthrobacter sp. strain MIS38 by electroporation. Electrotransformation was optimized; a square wave pulse of 1 kV cm1 electric field strength for 0.5 ms duration yielded 3 105 transformants per microgram plasmid DNA. The host– vector system expressed a lipase gene of Arthrobacter sp. MIS38 in other strains. Oligonucleotide probes for cheese surface bacteria, including Arthrobacter/Micrococcus, were developed. This is an important contribution to identify the smear microbiota. Sequences were chosen from sites of the 16S rRNA. Because of the intermixing of some Arthrobacter and Micrococcus species and the significant heterogeneity of this cluster, it was not possible to design an Arthrobacter/Micrococcus specific oligonucleotide for colony hybridization that fits all the species and at the same time excludes related species (e.g., Dermatophilus congolensis). The few species from other genera, however, also targeted do not live in the same habitat, namely the cheese surface. A total of 17 bacteriophages, active against 19 soil arthrobacters, have been detected in concentrated samples of river water and sewage. Bacteriophages have not been found in either concentrated or unconcentrated soil extracts because of the greater viral retention capacity of the soil and to the fluctuations in the phage sensitivity of soil bacteria. Electron microscopic studies showed morphologies characteristic of Bradley’s groups B and C. The G þ C content of bacteriophages was in the range 60.2–65.3% which agrees with the G þ C range of arthrobacters. Isolation of bacteriophages for A. globiformis depends on the nutritional features of the soil. Indigenous host cells in nonamended soil are present in a nonsensitive spheroid state, with the cells becoming sensitive to the phage in a ratelimiting fashion as outgrowth occurs.
Arthrobacter
Role in Foods Arthrobacters frequently are encountered in foods. They may occur as ineffective inhabitants, but when at high cell concentrations, they may indicate inadequate hygiene. They play an important role in biodegrading agrochemicals and in the ripening of smear surface–ripened cheeses.
Vegetables Arthrobacters are distributed largely among the indigenous bacterial biota of soils. They are not limited to any particular soil but are found in sandy, clay, peaty, grassland, and tropical soils. They occur in the rhizosphere and in the epiphytic part of the plants. In the rhizosphere, they release growth factors and auxin, but they also are sensitive to soil bacteriostasis, especially to wheat root secretions. Arthrobacters may abundantly populate vegetables during and after food processing. Arthrobacter globiformis is largely found in healthy sugarbeet roots stored at 5 C. Because Arthrobacter spp. may be associated with the seed before the fruit opens, they may spread to the aerial parts of many higher plants (e.g., soybean). Arthrobacters are found in ready-to-use vegetables. Most of the isolates in frozen peas, beans, and corn correspond to Arthrobacter spp. Blanched vegetables may still contain arthrobacters. Because cells do not survive blanching, airborne contamination of the surfaces of processing equipment could be another source of infection. Arthrobacters play a role in controlling some soil-borne pathogens. Arthrobacter spp. have been recovered during culture of the causal organism of pitch canker of Southern pines, Fusarium moniliforme var. subglutinans. Electron microscopic observations revealed that the hyphae of the pathogen fungus growing near Arthrobacter spp. were enlarged, producing many vesicular-like structures. The surface of these hyphae was warped and wrinkled in comparison with normal hyphae. Arthrobacters are chitinolytic bacteria. Enzymes, capable of hydrolyzing polymers, lyse fungal hyphae and hence inhibit growth. Inhibition of Aspergillus spp. and Penicillium spp. was shown in stored cereal grains. Arthrobacter strains capable of degrading swainsonine, an indolizidine alkaloid contained in poisonous plants Oxytropis and Astragalus spp. and harmful to livestock, are considered potential candidate for a novel biotechnological use in feed industry.
Meat, Eggs, and Fish Catalase-positive bacteria with a rod–coccus growth cycle such as Corynebacterium, Microbacterium, and Arthrobacter often are isolated in fresh beef. They also are recovered from turkey giblets and traditional bacon stored aerobically. Microbial and chemical changes in aerobically stored bacon fall into two phases, the first of microbial growth and reduction of nitrate to nitrite, and the second in which most of the accumulated nitrite is broken down to unknown products. Arthrobacter– Corynebacterium are mainly associated with the last phase of bacon storage. Poultry litter contains yellow strains and strains
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growing on citrate plus ammonia, classified as A. citreus and A. aurescens. Arthrobacter spp., together with Pseudomonas spp., are the most prevalent bacteria found in liquid egg. A study conducted on microbial contamination of eggshells and egg packing materials showed that arthrobacters accounted for approximately 13% of the total number of isolates. Dust, soil, and fecal material are the most common sources of contamination. Arthrobacters do not cause spoilage of shell eggs and, in liquid, egg may not affect keeping quality but may indicate the possibility of contamination by spoilage organisms present in soil or fecal material. Arthrobacter spp. together with Moraxella, Pseudomonas, Acinetobacter, and Flavobacterium–Cytophaga spp. are the microorganisms predominantly associated with raw Pacific and Gulf coast shrimps. In peeled shrimp, the number and composition of the microbiota vary, but arthrobacters may remain constant. They are isolated in greater proportion from plants that minimally washed raw shrimp. Pond-reared shrimps also contain arthrobacters, and the pond water frequently yields more than 90% of such bacteria. Arthrobacters are commonly isolated from Dungeness crab (Cancer magister) meat, both from retails and intestine. They increase in proportion during processing of crab meat, because they populate the brine and are less sensitive to cooking, but they do not multiply in refrigerated crab meat.
Milk and Cheese Arthrobacter spp. are part of the microbiota of raw milk and in some cases constitute the most predominant of the non-sporeforming Gram-positive rod-shaped bacteria. Psychrotrophic strains increase during long-term storage of refrigerated raw milk. Some psychrotrophic isolates of Arthrobacter spp. synthesize a b-galactosidase with similarities to that of E. coli but which differed in the optimal temperature, w20 C lower. Removal of lactose from refrigerated milk or whey was proposed as a use of this b-galactosidase to produce low-lactose products during shipping and storage. Bacteria such as Brevibacterium, Arthrobacter, Micrococcus, and Corynebacterium spp. are dominant at the end of ripening of smear surface–ripened cheeses, such as Limburger, Brick, Münster, Saint–Paulin, Appenzeller, Trappist, Livarot, Maroilles, Taleggio, and Quartirolo. During the initial stages of ripening, the surface microbiota is dominated by yeasts and molds, which cause an increase in pH due to a combination of lactate utilization and ammonia production, enabling the growth of acid-sensitive bacteria such as Arthrobacter spp. Lowmolecular-weight compounds (peptides, amino acids, fatty acids, etc.) are produced on the surface through the coupled action of various extracellular hydrolases produced by the smear microbiota. The diffusion of these compounds to the interior of the cheese is required for the development of the characteristic qualities of these cheeses. Arthrobacter arilaitensis is one of the major bacterial species found at the surface of cheeses, especially in smear-ripened cheeses, where it contributes to the typical color, flavor, and texture properties. The A. arilaitensis Re117 genome has been sequenced and comparative genomic analyses revealed an
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Arthrobacter
extensive loss of genes associated with catabolic activities, presumably as the result of adaptation to the cheese surface niche. Arthrobacter arilaitensis Re117 has the complete pattern of enzymes needed for the catabolism of the major carbon substrates that are present at the cheese surface (e.g., fatty acids, amino acids, and lactic acid). Other specific features that promote adaptation are the capacity to catabolize D-galactonate, a high number of transporters for glycine-betaine and related osmolytes, two siderophore biosynthesis gene clusters, and a high number of Fe3þ/siderophore transport systems. Arthrobacters, together with yeasts and Brevibacterium linens, were the main microorganisms found in Limburger cheese during ripening; yeasts dominate up to 9 days of ripening, B. linens reaches its highest level in 35-day-old cheese, but Arthrobacter spp. account for w78% of the total count. Gray and greenish-yellow Arthrobacter spp. have the highest proteolytic activity among the surface microbiota. Coryneform bacteria from 21 brick cheeses (including Limburger, Romadur, Weinkäse, and Harzer) from 6 German dairies were identified as A. nicotianae, B. linens, Brevibacterium ammoniagenes, and Corynebacterium variabilis. After an initial variability of the surface microbiota of the Tilsiter cheeses from 14 Austrian cheese plants, the decrease of the yeast cell numbers is followed by the growth of a mixed population composed of A. citreus, A. globiformis, A. nicotianae, Arthrobacter variabilis, B. linens, and B. ammoniagenes. The yellow–green coloration of the Taleggio cheese surface is mainly caused by A. globiformis and A. citreus. Moreover, it was hypothesized that the ability of Arthrobacter spp. to synthesize volatile sulfur compounds from methionine could have a marked impact on the global odor of ripened cheeses. Even though the role during ripening is only partially known, other Italian cheeses such as Quartirolo, Robiola, and Fontina contain arthrobacters on the cheese surface. Also mold surface–ripened cheeses such as Brie and Camembert from 20 days until the end of ripening are largely populated by Brevibacterium and Arthrobacter spp. together with fungal hyphae and yeast cells. Mixed cultures suitable for surface ripening have been developed. Cultures (single or mixed species of Arthrobacter and yeasts) are added as starters during the manufacture of Tilsit cheese. Arthrobacter citreus has a significant effect in cheese proteolysis. Again in Tilsit cheese, a starter composed of Lactobacillus helveticus, Lactobacillus delbrueckii, B. linens, Arthrobacter spp., and Geotrichum candidum or Debaryomyces hansenii was used. Mixed cultures of arthrobacters with yeasts and micrococci are used for red smear cheeses. Nevertheless, the successful establishment of arthrobacters within the resident microbial ripening consortia of smear surface–ripened cheeses is still debated, because they are markedly affected by competition. Despite their high cell numbers in the smear, the role of extracellular enzymes of Arthrobacter spp. probably is underestimated with respect to B. linens. Two extracellular serine proteinases of A. nicotianae ATCC 9458 show characteristics that indicate a significant contribution to proteolysis on the surface of smear-ripened cheeses: high activity at the pH and temperature of cheese ripening, tolerance to NaCl, and extensive activity on as1- and, especially, b-caseins. Because only plasmin and, probably, cathepsin D have a certain role in
b-casein hydrolysis in cheeses, the activity of Arthrobacter enzymes should be fundamental. Four strains of A. nicotianae isolated from red smear cheese showed inhibition to Listeria spp. Inhibition is more effective against Listeria innocua and Listeria ivanovii than against Listeria monocytogenes. The inhibitory compound loses activity upon heating and has a molecular mass greater than 12–14 kDa.
Miscellaneous Biotechnological Potentialities Arthrobacters are a commercially important host for the production of valuable bioproducts. Some species are used to produce sweeteners, phytohormones, riboflavin, and a-ketoglutaric acid. Coryneform bacteria, including Arthrobacter spp., are the most important microbial group for the commercial production of amino acids (e.g., glutamic acid). A mutant of Arthrobacter, strain DSM 3747, was used for the production of Lamino acids from D,L-5 monosubstituted hydantoins. Arthrobacter sp. MIS38 isolated from oil spills produces no glycolipids and only a lipopeptide. The lipopeptide (arthrofactin) is an effective biosurfactant. Arthrofactin is at least five times more effective than surfactin (the best-known lipopeptide biosurfactant). Moreover, arthrofactin is a better oil remover than synthetic surfactants, such as Triton X-100 and sodium dodecyl sulfate. The potential of arthrobacters has been evaluated for the production of flavor metabolites, precursors and enhancers, and has found useful application in the synthesis of terpenes and sweeteners, such as D-xylose. Some enzymatic activities of arthrobacters have been proposed for specific technology purposes. For instance, a thermoalkalophilic and cellulase-free xylanase, which was synthesized by Arthrobacter sp. MTCC 5214 during solid-state fermentation of wheat bran, was evaluated for prebleaching of kraft pulp. A thermostable alkaline lipase from Arthrobacter sp. BGCC no. 490, which was characterized by high activity in the presence of acetone, isopropanol, ethanol, and methanol, was proposed for applications in the detergent industry.
Biodegradation of Agrochemicals and Pollutants Arthrobacters are capable of participating in the degradation of various compounds deriving from agrochemicals, pharmaceuticals, and toxic wastes, in polluted temperate and cold environments. Polychlorinated phenols such as 4-chlorophenol may be released accidentally into the environment. Arthrobacter ureafaciens degrades 4-chlorophenol through the elimination of the chloro-substituent and the production of the hydroquinone as transient intermediates. Other para-substituted phenols are metabolized through the hydroquinone pathway. Picolinic acid (2-carboxylpyridine), structurally similar to the herbicide picloram (4-amino-3,5,6-trichloropicolinic acid) and the photolytic product of another herbicide, diquat (1,10 dimethyl-4,40 -bipyridylium ion), is used as carbon and energy sources by Arthrobacter picolinophilus. Diazinon O,O-diethyl O-[4-methyl-6-(propan-2-yl)pyrimidin-2-yl] phosphorothioate added to paddy water for controlling stem borer, leafhopper, and planthopper pests of rice is degraded by arthrobacters. One
Arthrobacter isolate from treated paddy water metabolized it in the presence of ethyl alcohol or glucose. Arthrobacter oxydans, isolated from soil, degrades the phenylcarbamate herbicides phenmedipham methyl (3-methylcarbaniloyloxy) carbanilate and desmedipham (3-ethoxycarbonylaminophenyl-phenylcarbamate), by hydrolyzing their central carbamate linkages (carbamate hydrolase). Phenmedipham and desmedipham are hydrolyzed at comparable rates, whereas phenisopham, a compound with an additional alkyl substitution at the carbamate nitrogen, is not hydrolyzed. In some cases, synthetic aromatic compounds, such as m-chlorobenzoate, may account only for incomplete degradation. The benzoate-oxidizing enzyme of Arthrobacter spp. produces 4-chlorocatechol from m-chlorobenzoate, which is not further degraded by catechol-metabolizing enzymes. Cometabolism could result from an accumulation of some toxic product or from an inability of the organism to carry the metabolism to a stage at which the carbon could be assimilated. Arthrobacters would be promising candidates for bioremediation of contaminated soils and water. A biofilter using granular activated carbon with coimmobilized Paracoccus sp. CP2 and Arthrobacter sp. CP1 achieved the complete degradation of trimethylamine, a teratogenic and maleodorous pollutant, which frequently was found in effluents from fishmeal manufacturing process. The ability to degrade trimethylamine also was found in Arthrobacter protophormiae. Arthrobacter sp. strain JBH1 was able to degrade nitroglycerin in soil through a pathway that involves the conversion of nitroglycerin to glycerol, via 1,2-dinitroglycerin and 1-mononitroglycerin, with concomitant release of nitrite. Arthrobacter aurescens strains, which were isolated from contaminated sites and possess atrazine-degrading genes trzN, atzB, and atzC, were capable of degrading atrazine in contaminated soil and wastewater in bioremediation trials. Arthrobacter sp. strain IF1 had the capacity to grow on 4-fluorophenol (4-FP), as the sole source of carbon and energy, through the conversion of 4-FP into hydroquinone via a twocomponent monooxygenase system. Other compounds biodegraded in contaminated soil by Arthrobacter sp. are 4-chlorophenol (Arthrobacter chlorophenolicus, Arthrobacter defluvii sp. nov.), nicotine (Arthrobacter nicotinovorans), 4-nitroguaiacol (Arthrobacter nitroguajacolicus sp. nov.), acrylonitrile (A. nitroguajacolicus sp. nov.), p-nitrophenol (A. chlorophenolicus, A. protophormiae), phenol (A. citreus), imazaquin (A. crystallopoietes), and phthalic acid esters, 4-fluorocinnamic acid, phthalate esters, tris (1,3-dichloro-2-propyl) phosphate, dibenzothiophene, carbazole, quinaldine, and 4-chlorobenzoic acid. Arthrobacters colonize heavy metal–contaminated sites. The multiple metal-resistant Arthrobacter ramosus strain was found to withstand and bioaccumulate several metals, such as cadmium, cobalt, zinc, chromium, and mercury. It may reduce and detoxify redox-active metals, like chromium and mercury. Similar activities were found in A. globiformis. The use of Arthrobacter viscosus and A. aurescens for removing chromium in water and soil was reported. The potential of the chromium reductase of Arthrobacter rhombi to reduce hexavalent chromium (Cr(VI)) was evaluated. The capacity of Arthrobacter sp. to remove Cu2þ ions from aqueous solution also was demonstrated.
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Arthrobacters may contribute significantly to wastewater treatment and groundwater remediation problems because of the accidental release of gasoline in the environment. There are difficulties with the biological treatment of gasoline oxygenates such as methyl t-butyl ether. Ethers tend to be quite resistant to biodegradation by microorganisms. Pure cultures of Arthrobacter spp. are able to degrade methyl t-butyl ether by using it as a carbon source. Phenantrene- and anthracene-degrading strains belonging to Arthrobacter phenanthrenivorans sp. nov. were characterized. Nondegradable and persistent compounds such as plastic, polyethylene, polycarbonate, and polyester pose a threat to the environment. Bacteria may be considered as potent utilizers of these compounds because of their ability to produce various enzymes needed for breakdown of such compounds. In view of these factors, Arthrobacter and Enterobacter strains were used for in vitro biodegradation, showing a significant utilization of polycarbonate.
Involvement in Clinical Specimens Strains of Arthrobacter spp. have been very rarely described as causing disease in humans (case reports described occasional subacuted infective endocarditis, bacteremia, postoperative endophthalmitis, Whipple disease-like syndrome, and phlebitis). In recent years, however, clinical microbiologists have begun to fully recognize the enormous diversities of coryneform bacteria in clinical specimens and a large number of strains isolated in clinical bacteriology laboratories were unambiguously assigned to the Arthrobacter spp. through 16S rDNA gene sequence and peptidoglycan analyses. New species, such as Arthrobacter cumminsii and Arthrobacter woluwensis, were proposed. Arthrobacter cumminsii might be the most frequently encountered Arthrobacter in clinical specimens, because it was isolated from patients with urinary tract and deep tissue infections, and external otitis. Arthrobacter cumminsii seems to be a microorganism with no or rather low pathogenicity as cases of severe, life-threatening infections were not observed in patients. It might be the only bacterial agent for selected cases of urinary tract infections. It is likely that A. cumminsii is part of the normal human skin and mucosa membrane biota, in particular, in the genitourinary tract. Arthrobacter oxydans, Arthrobacter luteolus, Arthrobacter albus, and Arthrobacter scleromae also were isolated from human clinical specimens. Arthrobacter sanguinis and, the creatinehydrolyzing species, Arthrobacter creatinolyticus were isolated from human blood and urine, respectively. The major part of the Arthrobacters isolated from clinical specimens exhibited susceptibility to b-lactams, doxycycline, gentamicin, linezolid, rifampin, and vancomycin. Arthrobacter equi and Arthrobacter nasiphocae were isolated from animal sources (horse and common seal, respectively). Recently, lyophilized Arthrobacter cells were included in a vaccine for treatment or prevention of piscirickettsiosis in salmonid fish.
See also: Brevibacterium; Cheese: Mold-Ripened Varieties; Cheese: Microflora of White-Brined Cheeses; Fish: Spoilage of
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Fish; Spoilage of Meat; Milk and Milk Products: Microbiology of Liquid Milk.
Further Reading Euzéby, J.P., List of Prokaryotic Names with Standing in nomenclature – genus Arthrobacter, www.bacterio.cict.fr. Funke, G., Pagano-Niederer, M., Sjödén, B., Falsen, E., 1998. Characteristics of Arthrobacter cumminsii, the most frequently encountered Arthrobacter species in human clinical specimens. Applied and Environmental Microbiology 36, 1539–1543. Heyrman, J., Verbeeren, J., Schumann, P., Swings, J., De Vos, P., 2005. Six novel Arthrobacter species isolated from deteriorated mural paintings. International Journal of Systematic and Evolutionary Microbiology 55, 1457–1464. Jones, D., Keddie, R.M., 2006. The genus Arthrobacter. Prokariotes 3, 945–960.
Keddie, R.M., Collins, M.D., Jones, D., 1986. Genus arthrobacter conn and dimmick 1947, 300AL. In: Sneath, P.H., Mair, N.S., Sharpe, M.E., Holt, J.G. (Eds.), Genus Arthrobacter, Bergey’s Manual of Systematic Bacteriology, vol. 2. Williams & Wilkins, Baltimore, p. 1288. Koch, C., Rainey, F.H., Stackebrandt, E., 1994. 16S rDNA studies on members of Arthrobacter and Micrococcus: and aid for their future taxonomic restructuring. FEMS Microbiology Letters 123, 167–172. Kolloffel, B., Burri, S., Meile, L., Teuber, M., 1997. Development of 16S rRNA oligonucleotide probes for Brevibacterium, Micrococcus/Arthrobacter and Microbacterium/Aureobacterium used in dairy starter cultures. Systematic and Applied Microbiology 20, 409–417. Mages, I.S., Frodl, R., Bernard, K.A., Funke, G., 2008. Identities of Arthrobacter spp. and Arthrobacter-like bacteria encountered in human clinical specimens. Journal of Clinical Microbiology 46, 2980–2986. Smacchi, E., Fox, P.F., Gobbetti, M., 1999. Purification and characterization of two extracellular proteinase from Arthrobacter nicotianae 9458. FEMS Microbiology Letters 170, 327–333.
General Characteristics
Ecology
Arthrobacter is a genus of mainly soil bacteria whose major distinguishing feature is a rod–coccus growth cycle. Irregular rods in young cultures are replaced by stationary-phase coccoid cells, which when transferred to fresh medium, produce outgrowths to give irregular rods again. Coccoid cells may assume large and morphologically aberrant forms when in conditions of severe nutritional stress. Both rod and coccoid forms are Gram-positive but easily may be decolorized. Gramnegativity may appear in midexponential- to stationary-phase cells. Cells do not form endospores; they are nonmotile or motile by one subpolar or a few lateral flagella, obligate aerobes, and catalase positive. Their metabolism is respiratory, never fermentative (little or no acid is formed from sugars), and the nutrition is nonexacting. The G þ C content of the DNA is in the range of 59–66 mol% (actinomycete branch) and the cell wall peptidoglycan contains lysine as diamino acid. A total of 15 species of Arthrobacter (sensu stricto) were reported in the Bergey’s Manual of Systematic Bacteriology until 2000, whereas about 70 species now are recognized (Euzéby: list of prokaryotic names with standing in nomenclature – Genus Arthrobacter) Two groups of species, Arthrobacter globiformis/Arthrobacter citreus and Arthrobacter nicotianae/ Arthrobacter sulfureus, are accepted on the basis of DNA–DNA homology, 16S rRNA cataloging studies, peptidoglycan structure, teichoic acid content, and lipid composition (Table 1). On the basis of 16S rDNA studies, the separation of Arthrobacter into two groups of species has no phylogenetic validation. Members of the second group (e.g., A. nicotianae) are significantly more closely related to certain members of the first group (e.g., A. globiformis) than members of the first group are related to each other (e.g., A. globiformis vs. A. citreus). Nutritional versatility is characteristic: carbohydrates, organic acids, amino acids, aromatic compounds, and nucleic acids are used as carbon and energy sources. A comparison between some metabolic properties of A. globiformis and A. nicotianae is reported in Table 2. With the exception of biotin, vitamins or other organic growth factors are not required. Arthrobacters mainly use inorganic nitrogen. Arthrobacter citreus is a notable exception as it uses a more limited range of compounds as energy and carbon sources and requires complex growth factors in addition to a siderophore, such as ferrichrome or mycobactin, for growth. The optimum temperature for growth is 25–30 C, and most arthrobacters grow in the range of about 10–35 C. Many strains also grow at 5 C and a few grow at 37 C. Growth at 37 C is influenced by the culture medium. On a phylogenetic basis (homology within the 16S ribosomal gene), the Arthrobacter species could not be separated from members of the genus Micrococcus. Both are included in the class: Actinobacteria, Subclass V: Actinobacteridae, Order I: Actinomycetales, Suborder IX: Micrococcineae, Family I: Micrococcaceae (see Bergey’s Manual of Systematic Bacteriology, 2011).
Arthrobacters are numerically important among the indigenous bacterial biota of soils and rhizospheres. Nutritional versatility, extreme resistance to drying, and starvation ensure their predominance in soils of different geographic locations. Soil acidity decreases cell viability. Psychrotrophic strains are abundant in terrestrial subsurface environments and occur in the Arctic and Antarctic, glacier silts, alpine glacier cryoconites, and ice caves. Isolates have been found in oil brines raised from soil layers at w200–700 m depth. Arthrobacter spp. are relatively common on the aerial surface of plants, including flowers. Marine and freshwater fish and other seafoods contain arthrobacters. They occur in shark spoilage, eviscerated freshwater fish, fish-pen slime, and shrimp. Other populated habitats include sewage, brewery waste, wastewater reservoir sediments, deep poultry litter, dairy waste-activated sludge, and the surface of smear surfaceripened cheeses. Recently, different novel species have been isolated from archaeological mural paintings. Arthrobacter spp. were also isolated from human and veterinary clinical sources.
Encyclopedia of Food Microbiology, Volume 1
Culture Media Arthrobacter spp. normally are isolated from soil by plating on nonselective media because they are an appreciable proportion of the aerobic, cultivable population. Soil extract agar is used largely because it is sufficiently poor in carbon and energy sources. Possible modifications could include the addition of low concentrations of yeast extract and glucose to give higher counts, the incorporation of nystatin and cycloheximide to suppress fungi growth, and salt to reduce growth of Gramnegative bacteria. The isolation of arthrobacters in selective medium (Table 3) gives counts several times higher than those on nutritionally poor medium. The combination of 0.01% cycloheximide and 2.0% NaCl is effective in inhibiting fungi and most Streptomyces spp., Nocardia spp., and Gram-negative bacteria. Methyl red (150 mg ml1) inhibits other Gram-positive bacteria but does not affect arthrobacters.
Metabolism and Enzymes Carbohydrate dissimilation by Arthrobacter spp. falls into two groups. Arthrobacter globiformis, Arthrobacter ureafaciens, and Arthrobacter crystallopoietes primarily use the Embden– Meyerhof–Parnas and, to a lesser extent, the hexose monophosphate (HMP) pathways. Arthrobacter pascens and Arthrobacter atrocyaneus use the Entner–Doudoroff and HMP pathways. The pyruvate formed is oxidized by the tricarboxylic acid cycle, and the cytochrome system mediates the terminal
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70 Arthrobacter
Table 1
Characteristics of some Arthrobacter speciesa A. A. crystall- A. A. globiformis opoietes pascens ramosus
A. A. histidinoaurescens lovorans
A. ilicis
A. ureafaciens
A. A. atrocyaneus oxydans
A. citreus
A. nicotianae
A. protophormiae
A. A. uratoxydans sulfureus
Peptidoglycan type A3a variationb A4a variationb MK-9(H2)c MK-8c Teichoic acid Cell wall sugars
Lys-Ala
Lys-Ala
Lys-Ala
Lys-Ala
þ – þ – – Gal, Glu
þ – þ – – Gal, Glu
þ – þ – – Gal, Rha, Man
Lys-AlaThr-Ala þ – þ – – Gal, Glu
Lys-AlaThr-Ala þ – þ – – Gal, Rha, Man
Lys-AlaThr-Ala þ – þ – – Gal (Man)
Lys-Ser-Ala
þ – þ – – Gal, Glu
Lys-AlaThr-Ala þ – þ – – Gal (Man)
Lys-SerThr-Ala þ – þ – – Gal, Glu
Lys-ThrAla þ – þ – – Gal
Lys-AlaGlu – þ – þ þ ND
Lys-AlaGlu – þ – þ þ ND
DNA homologye Starch hydrolysis Motility
100%f
16%f
35%f
25%f
22%f
36%f
ND
31%f
24%f
50%f
18%f
Lys-AlaGlu – þ – þ þ Gal, Glc (one strain) 100%g
39%g
ND
– þ d d þ Gal, Glc (one strain) 22%g
þ
–
þ
–
þ
–
–
–
þ
þ
–
þ
–
–
–
–
–
–
þ
–
–
þ
–
þ
–
þ
–
–
þh
þh
Characteristics
þ – þ – – Gal, Glu (Man)
Lys-Glu
Symbols: þ, 90% or more of the strains are positive; , 90% or more of the strains are negative; (), conflicting reports on occurrence; ND, no data. Within the type A peptidoglycan (cross-linkage between positions 3 and 4 of the peptide subunits), two groups occur: A3a variations (the interpeptide bridge of peptidoglycan contains only monocarboxylic acids and/or glycine) and A4a variations (the interpeptide bridge always contains a dicarboxylic acid and in most strains also alanine). c MK-9(H2), dihydrogenated menaquinones with nine isoprene units as major components. MK-8, unsaturated menaquinones with eight isoprene units as major components. d A. sulfureus either contains MK-9 as the major menaquinone or comparable amounts of MK-9 and MK-10. e Homology index is expressed as percent of 3H-DNA bound to a certain disc DNA relative to the homologous reaction. f DNA homologies of named strains versus A. globiformis DSM 20125. g DNA homologies of named strains versus A. nicotianae DSM 20123. h A. uratoxydans, rods, motile by peritrichous flagella or nonmotile. A. sulfureus, rods motile by one or few lateral flagella or nonmotile. a
b
Arthrobacter Table 2 Comparison of some metabolic features between Arthrobacter globiformis DSM 20124 and Arthrobacter nicotianae DSM 20123a
Metabolic properties Utilization of 4-Aminobutyrate 5-Aminovalerate Malonate 4-Hydroxybenzoate Glyoxylate 2-Ketogluconate L Leucine L-Asparagine L-Arginine L-Histidine L-Xylose D-Ribose L-Arabinose D-Galactose L-Rhamnose D-Xylitol m-Inositol 2,3-Butylene glycol Glycerol Nicotine Hydrolysis of Xanthine Casein
A. globiformis DSM 20124
A. nicotianae DSM 20123
þ – þ þ þ þ – þ þ þ þ þ þ þ þ þ þ – þ –
þ þ þ þ – – þ þ – þ þ þ þ þ – – – þ þ þ
þ þ
– þ
a Symbols: þ, 90% or more of the strains are positive; , 90% or more of the strains are negative.
Table 3 Selective medium of Hagedorn and Holta for the isolation of Arthrobacter spp. Compound
Quantity
Trypticase soy agar Yeast extract NaCl Cycloheximide Methyl redb Agar
0.4% 0.2% 2.0% 0.01% 150 mg ml1 1.5%
a
Plate counts are made by spreading 0.1 ml amounts of suitable dilutions over the surface of sterile medium in Petri dishes. Peptone solution (0.5%, wt vol1) is used as the diluent. b The methyl red is filter sterilized and added aseptically to the autoclaved, cooled medium. The medium is adjusted to the pH of the particular soil being examined.
electron transport. When acetate is used as the carbon and energy source, arthrobacters must produce tricarboxylic acid cycle intermediates for biosynthetic purposes and should have mechanisms to produce acceptor molecules for C2 units. The glyoxylate cycle serves this purpose: Key enzymes of this cycle have been found in Arthrobacter spp. when grown on acetate plus glycine. Arthrobacter globiformis grows on glycine as the sole carbon and energy source and converts this amino acid through serine into pyruvate. Pyruvate is converted into C4 dicarboxylic acids for the tricarboxylic acid cycle and also into phosphoenolpyruvate, as a precursor of carbohydrates. Additionally,
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nucleic acids (both DNA and RNA) are decomposed to produce uric acid, allantoin, and urea. Arthrobacters from soil, but not from cheese and fish, use both uric acid and allantoin as the sole sources of carbon, energy, and nitrogen. Arthrobacters carry out heterotrophic nitrification. Cells must be provided with a carbon compound to produce energy and to synthesize the carbon-containing products of nitrification. Ammonium is converted into an amide, which is then oxidized to acetohydroxamic acid. The latter is converted rapidly by a reversible reaction into free hydroxylamine, but it is also oxidized slowly to nitrosoethanol. Nitrite and nitrate are late products in this sequence. Nitrite and nitrate are formed from aliphatic nitro-compounds. Arthrobacters isolated from soil respire nitrate in the presence of oxygen, but, in contrast to other soil bacteria, do not synthesize periplasmic-type nitrate reductase. Soil arthrobacters grown with excess glucose and a limited amount of NHþ 4 , HPO4 , or SO4 are particularly rich in storage polysaccharides such as glycogen. Glycogen enables survival for prolonged periods of nitrogen depletion and at the same time provides energy and intermediates for protein synthesis when inorganic nitrogen is available. Glycogen has an exceptionally high degree of branching. Extracellular polysaccharides are produced commonly by arthrobacters. Polysaccharides may consist of glucose, galactose, and uronic acid or mannuronic acid. Strains synthesize b-fructofuranosidase, which transfers the fructosyl residues of sucrose to aldoses or ketoses, to produce hetero-oligosaccharides. Such compounds protect against predation by protozoa in natural environments and never are used as a carbon and energy source by producers. The majority of Arthrobacter spp. isolated from soil, milk, cheese, and activated sludge are highly proteolytic. When actively growing in the soil, arthrobacters produce extracellular proteinases. Synthesis is repressed by high amino acid concentration. Enzymes are stable. The proteinase of A. ureafaciens consists of a single peptide chain of 221 amino acid residues cross-linked by two disulfide bridges, which, in part, explain its stability. Proteinases may have very high temperature optima, w70 C, and milk-clotting properties. Two extracellular serine proteinases with molecular masses of about 53–55 kDa and 70–72 kDa have been purified from A. nicotianae isolated from smear surface cheese. The enzymes differ with respect to temperature optimum (55–60 C and 37 C), tolerance to low values of pH and temperature, heat stability, sensitivity to ethylenediaminetetraacetic acid, and sulfhydryl blocking agents and hydrophobicity. Peptidases have been less studied than proteinases. An aminopeptidase of broad specificity, a proline iminopeptidase with activity against long peptides with a free N-terminal proline, and an imidodipeptidase (prolidase), which hydrolyzes only dipeptides, were found in cell extracts of soil Arthrobacter spp. Arthrobacters, especially those isolated from soil, have enzymes that enable them to degrade unusual and polymeric compounds. Strains that use levoglucosan (1,6-anhydro-b-Dglucopyranose) possess a levoglucosan dehydrogenase. Glucose is produced from levoglucosan by three steps: dehydrogenation, intramolecular hydrolysis, and nicotinamide adenine dinucleotide–dependent reduction. Levoglucosan dehydrogenase catalyzes the initial step. This pathway is
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distinct from those reported for soil yeasts and fungi. A levanase, which rapidly hydrolyzes levan (b-D-fructose polymer) in an endo-type manner to produce a series of levanoligosaccharides, was found. Pectolytic activity as well as the capacity to degrade another polyuronide such as alginic acid seems rather rare in arthrobacters. Methylamine oxidase, used to assimilate carbon in the form of methylamine or ethylamine, is synthesized by methylotroph Arthrobacter strains. It oxidizes primary amines methyl-, ethyl-, propyl-, butyl-, ethanol-, and benzylamine, but not tyramine, spermine, putracine, trimethylamine, and dimethylamine. Only O2 acts as a reoxidizing substrate for this enzyme. A maltooligosyl-trehalose synthase, which converts maltooligosaccharide into maltooligosyl trehalose by intramolecular transglycosylation, and a maltooligosyl-trehalose trehalohydrolase, which hydrolyzes the a-1,4-glucosidic bond between maltooligosyl and trehalose moieties, have been found in Arthrobacter spp., which accumulate trehalose. Arthrobacter globiformis produces an inulinase, which degrades inulin through an exo-type reaction. Choline oxidase has been found in A. pascens and A. globiformis. This is a cytosolic flavoprotein, hydrogen-peroxide-forming oxidase that oxidizes choline to produce glycine-betaine by a two-step reaction with betaine aldehyde as the intermediate. Betaine acts as a nontoxic osmolyte, highly compatible with metabolic functions at high cytoplasmic concentrations and contributes to turgor adjustment in cells subjected to osmotic stress.
Genetics and Bacteriophages Several genes of Arthrobacter spp. have been cloned and sequenced. The focus here is on genes for food enzymes. A 5.1 kbp genomic DNA fragment was cloned from trehalose-producing Arthrobacter sp. strain Q36. Sequence analysis revealed two open reading frames (ORFs) of 2325 and 1794 bp, encoding maltooligosyl-trehalose synthase and maltooligosyl-trehalose trehalohydrolase. A novel trehalose synthase gene (treS) from Arthrobacter aurescens CGMCC was cloned and expressed in Escherichia coli. Enzymes have several regions common to the a-amylase family. Some arthrobacters infrequently produce b-galactosidase when grown in lactose minimal media. The gene has similarities with the E. coli lacZ gene. When DNA was transformed into an E. coli host, three fragments each encoding a different b-galactosidase isoenzyme were obtained. The nucleotide sequence of the smallest fragment has no total similarity with the lacZ family but has regions similar to b-galactosidase isoenzymes from Bacillus stearothermophilus and Bacillus circulans. Different b-galactosidase genes were found in Arthrobacter sp. ON14 (galA and galB), Arthrobacter sp. 20B (bgaS), Arthrobacter sp. SB (bgaS3), and Arthrobacter psychrolactophilus F2 (bglA). The gene-encoding inulin fructotransferase was sequenced in A. globiformis S14-3 and Arthrobacter sp. H65-7. The two genes share only 49.8% homology and the sequence analysis of the ift gene from strain H65-7 consists of a single ORF of 1314 bp that encodes a signal peptide of 32 amino acids and a mature protein of 405 amino acids. The gene encoding an extracellular isomalto-dextranase (imd) was isolated from the chromosome of A. globiformis T6 and expressed in E. coli. A single ORF consisting of 1926 bp that encodes a polypeptide composed of a signal peptide of 39
amino acids and a mature protein of 602 amino acids was found. The primary structure has no significant homology with the structures of any other reported carbohydrases and the enzyme differs in that it is capable of hydrolyzing dextran by releasing only isomaltose units from dextran chains. Isomaltose inhibits the biosynthesis of mutan, which is the major component of dental plaque and may be of significant importance in the prevention of dental caries. A gene for dextranase (aodex) also was found in Arthrobacter oxydans; it was cloned and expressed in E. coli. The pcd plasmid gene for phenylcarbamate hydrolase was sequenced in A. oxydans P52. It has significant homology with esterases of eukaryotic origin. Arthrobacter globiformis M6 produces a nonreducing oligosaccharide from starch, characterized by a cyclic structure consisting of four glucose residues joined by alternate a-1,4 and a-1,6 linkages and designated cyclic maltosyl-maltose (CMM). The gene encoding for the glycosyl-transferase (cmmA), which is involved in the synthesis of CMM from starch, was identified. Cholesterol oxidases are a group of flavin adenine dinucleotide (FAD)-dependent enzymes having important industrial applications and are used widely to determine cholesterol in food and blood serum through peroxidase-coupled assays. In addition, they are used in the production of starting material for the chemical synthesis of pharmaceutical steroids. The gene (choAA) encoding cholesterol oxidase from Arthrobacter simplex F2 was cloned and expressed in E. coli. A host–vector system based on pULRS8 containing the kanamycin-resistant gene, kan (Tn5), was used for transforming Arthrobacter sp. strain MIS38 by electroporation. Electrotransformation was optimized; a square wave pulse of 1 kV cm1 electric field strength for 0.5 ms duration yielded 3 105 transformants per microgram plasmid DNA. The host– vector system expressed a lipase gene of Arthrobacter sp. MIS38 in other strains. Oligonucleotide probes for cheese surface bacteria, including Arthrobacter/Micrococcus, were developed. This is an important contribution to identify the smear microbiota. Sequences were chosen from sites of the 16S rRNA. Because of the intermixing of some Arthrobacter and Micrococcus species and the significant heterogeneity of this cluster, it was not possible to design an Arthrobacter/Micrococcus specific oligonucleotide for colony hybridization that fits all the species and at the same time excludes related species (e.g., Dermatophilus congolensis). The few species from other genera, however, also targeted do not live in the same habitat, namely the cheese surface. A total of 17 bacteriophages, active against 19 soil arthrobacters, have been detected in concentrated samples of river water and sewage. Bacteriophages have not been found in either concentrated or unconcentrated soil extracts because of the greater viral retention capacity of the soil and to the fluctuations in the phage sensitivity of soil bacteria. Electron microscopic studies showed morphologies characteristic of Bradley’s groups B and C. The G þ C content of bacteriophages was in the range 60.2–65.3% which agrees with the G þ C range of arthrobacters. Isolation of bacteriophages for A. globiformis depends on the nutritional features of the soil. Indigenous host cells in nonamended soil are present in a nonsensitive spheroid state, with the cells becoming sensitive to the phage in a ratelimiting fashion as outgrowth occurs.
Arthrobacter
Role in Foods Arthrobacters frequently are encountered in foods. They may occur as ineffective inhabitants, but when at high cell concentrations, they may indicate inadequate hygiene. They play an important role in biodegrading agrochemicals and in the ripening of smear surface–ripened cheeses.
Vegetables Arthrobacters are distributed largely among the indigenous bacterial biota of soils. They are not limited to any particular soil but are found in sandy, clay, peaty, grassland, and tropical soils. They occur in the rhizosphere and in the epiphytic part of the plants. In the rhizosphere, they release growth factors and auxin, but they also are sensitive to soil bacteriostasis, especially to wheat root secretions. Arthrobacters may abundantly populate vegetables during and after food processing. Arthrobacter globiformis is largely found in healthy sugarbeet roots stored at 5 C. Because Arthrobacter spp. may be associated with the seed before the fruit opens, they may spread to the aerial parts of many higher plants (e.g., soybean). Arthrobacters are found in ready-to-use vegetables. Most of the isolates in frozen peas, beans, and corn correspond to Arthrobacter spp. Blanched vegetables may still contain arthrobacters. Because cells do not survive blanching, airborne contamination of the surfaces of processing equipment could be another source of infection. Arthrobacters play a role in controlling some soil-borne pathogens. Arthrobacter spp. have been recovered during culture of the causal organism of pitch canker of Southern pines, Fusarium moniliforme var. subglutinans. Electron microscopic observations revealed that the hyphae of the pathogen fungus growing near Arthrobacter spp. were enlarged, producing many vesicular-like structures. The surface of these hyphae was warped and wrinkled in comparison with normal hyphae. Arthrobacters are chitinolytic bacteria. Enzymes, capable of hydrolyzing polymers, lyse fungal hyphae and hence inhibit growth. Inhibition of Aspergillus spp. and Penicillium spp. was shown in stored cereal grains. Arthrobacter strains capable of degrading swainsonine, an indolizidine alkaloid contained in poisonous plants Oxytropis and Astragalus spp. and harmful to livestock, are considered potential candidate for a novel biotechnological use in feed industry.
Meat, Eggs, and Fish Catalase-positive bacteria with a rod–coccus growth cycle such as Corynebacterium, Microbacterium, and Arthrobacter often are isolated in fresh beef. They also are recovered from turkey giblets and traditional bacon stored aerobically. Microbial and chemical changes in aerobically stored bacon fall into two phases, the first of microbial growth and reduction of nitrate to nitrite, and the second in which most of the accumulated nitrite is broken down to unknown products. Arthrobacter– Corynebacterium are mainly associated with the last phase of bacon storage. Poultry litter contains yellow strains and strains
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growing on citrate plus ammonia, classified as A. citreus and A. aurescens. Arthrobacter spp., together with Pseudomonas spp., are the most prevalent bacteria found in liquid egg. A study conducted on microbial contamination of eggshells and egg packing materials showed that arthrobacters accounted for approximately 13% of the total number of isolates. Dust, soil, and fecal material are the most common sources of contamination. Arthrobacters do not cause spoilage of shell eggs and, in liquid, egg may not affect keeping quality but may indicate the possibility of contamination by spoilage organisms present in soil or fecal material. Arthrobacter spp. together with Moraxella, Pseudomonas, Acinetobacter, and Flavobacterium–Cytophaga spp. are the microorganisms predominantly associated with raw Pacific and Gulf coast shrimps. In peeled shrimp, the number and composition of the microbiota vary, but arthrobacters may remain constant. They are isolated in greater proportion from plants that minimally washed raw shrimp. Pond-reared shrimps also contain arthrobacters, and the pond water frequently yields more than 90% of such bacteria. Arthrobacters are commonly isolated from Dungeness crab (Cancer magister) meat, both from retails and intestine. They increase in proportion during processing of crab meat, because they populate the brine and are less sensitive to cooking, but they do not multiply in refrigerated crab meat.
Milk and Cheese Arthrobacter spp. are part of the microbiota of raw milk and in some cases constitute the most predominant of the non-sporeforming Gram-positive rod-shaped bacteria. Psychrotrophic strains increase during long-term storage of refrigerated raw milk. Some psychrotrophic isolates of Arthrobacter spp. synthesize a b-galactosidase with similarities to that of E. coli but which differed in the optimal temperature, w20 C lower. Removal of lactose from refrigerated milk or whey was proposed as a use of this b-galactosidase to produce low-lactose products during shipping and storage. Bacteria such as Brevibacterium, Arthrobacter, Micrococcus, and Corynebacterium spp. are dominant at the end of ripening of smear surface–ripened cheeses, such as Limburger, Brick, Münster, Saint–Paulin, Appenzeller, Trappist, Livarot, Maroilles, Taleggio, and Quartirolo. During the initial stages of ripening, the surface microbiota is dominated by yeasts and molds, which cause an increase in pH due to a combination of lactate utilization and ammonia production, enabling the growth of acid-sensitive bacteria such as Arthrobacter spp. Lowmolecular-weight compounds (peptides, amino acids, fatty acids, etc.) are produced on the surface through the coupled action of various extracellular hydrolases produced by the smear microbiota. The diffusion of these compounds to the interior of the cheese is required for the development of the characteristic qualities of these cheeses. Arthrobacter arilaitensis is one of the major bacterial species found at the surface of cheeses, especially in smear-ripened cheeses, where it contributes to the typical color, flavor, and texture properties. The A. arilaitensis Re117 genome has been sequenced and comparative genomic analyses revealed an
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Arthrobacter
extensive loss of genes associated with catabolic activities, presumably as the result of adaptation to the cheese surface niche. Arthrobacter arilaitensis Re117 has the complete pattern of enzymes needed for the catabolism of the major carbon substrates that are present at the cheese surface (e.g., fatty acids, amino acids, and lactic acid). Other specific features that promote adaptation are the capacity to catabolize D-galactonate, a high number of transporters for glycine-betaine and related osmolytes, two siderophore biosynthesis gene clusters, and a high number of Fe3þ/siderophore transport systems. Arthrobacters, together with yeasts and Brevibacterium linens, were the main microorganisms found in Limburger cheese during ripening; yeasts dominate up to 9 days of ripening, B. linens reaches its highest level in 35-day-old cheese, but Arthrobacter spp. account for w78% of the total count. Gray and greenish-yellow Arthrobacter spp. have the highest proteolytic activity among the surface microbiota. Coryneform bacteria from 21 brick cheeses (including Limburger, Romadur, Weinkäse, and Harzer) from 6 German dairies were identified as A. nicotianae, B. linens, Brevibacterium ammoniagenes, and Corynebacterium variabilis. After an initial variability of the surface microbiota of the Tilsiter cheeses from 14 Austrian cheese plants, the decrease of the yeast cell numbers is followed by the growth of a mixed population composed of A. citreus, A. globiformis, A. nicotianae, Arthrobacter variabilis, B. linens, and B. ammoniagenes. The yellow–green coloration of the Taleggio cheese surface is mainly caused by A. globiformis and A. citreus. Moreover, it was hypothesized that the ability of Arthrobacter spp. to synthesize volatile sulfur compounds from methionine could have a marked impact on the global odor of ripened cheeses. Even though the role during ripening is only partially known, other Italian cheeses such as Quartirolo, Robiola, and Fontina contain arthrobacters on the cheese surface. Also mold surface–ripened cheeses such as Brie and Camembert from 20 days until the end of ripening are largely populated by Brevibacterium and Arthrobacter spp. together with fungal hyphae and yeast cells. Mixed cultures suitable for surface ripening have been developed. Cultures (single or mixed species of Arthrobacter and yeasts) are added as starters during the manufacture of Tilsit cheese. Arthrobacter citreus has a significant effect in cheese proteolysis. Again in Tilsit cheese, a starter composed of Lactobacillus helveticus, Lactobacillus delbrueckii, B. linens, Arthrobacter spp., and Geotrichum candidum or Debaryomyces hansenii was used. Mixed cultures of arthrobacters with yeasts and micrococci are used for red smear cheeses. Nevertheless, the successful establishment of arthrobacters within the resident microbial ripening consortia of smear surface–ripened cheeses is still debated, because they are markedly affected by competition. Despite their high cell numbers in the smear, the role of extracellular enzymes of Arthrobacter spp. probably is underestimated with respect to B. linens. Two extracellular serine proteinases of A. nicotianae ATCC 9458 show characteristics that indicate a significant contribution to proteolysis on the surface of smear-ripened cheeses: high activity at the pH and temperature of cheese ripening, tolerance to NaCl, and extensive activity on as1- and, especially, b-caseins. Because only plasmin and, probably, cathepsin D have a certain role in
b-casein hydrolysis in cheeses, the activity of Arthrobacter enzymes should be fundamental. Four strains of A. nicotianae isolated from red smear cheese showed inhibition to Listeria spp. Inhibition is more effective against Listeria innocua and Listeria ivanovii than against Listeria monocytogenes. The inhibitory compound loses activity upon heating and has a molecular mass greater than 12–14 kDa.
Miscellaneous Biotechnological Potentialities Arthrobacters are a commercially important host for the production of valuable bioproducts. Some species are used to produce sweeteners, phytohormones, riboflavin, and a-ketoglutaric acid. Coryneform bacteria, including Arthrobacter spp., are the most important microbial group for the commercial production of amino acids (e.g., glutamic acid). A mutant of Arthrobacter, strain DSM 3747, was used for the production of Lamino acids from D,L-5 monosubstituted hydantoins. Arthrobacter sp. MIS38 isolated from oil spills produces no glycolipids and only a lipopeptide. The lipopeptide (arthrofactin) is an effective biosurfactant. Arthrofactin is at least five times more effective than surfactin (the best-known lipopeptide biosurfactant). Moreover, arthrofactin is a better oil remover than synthetic surfactants, such as Triton X-100 and sodium dodecyl sulfate. The potential of arthrobacters has been evaluated for the production of flavor metabolites, precursors and enhancers, and has found useful application in the synthesis of terpenes and sweeteners, such as D-xylose. Some enzymatic activities of arthrobacters have been proposed for specific technology purposes. For instance, a thermoalkalophilic and cellulase-free xylanase, which was synthesized by Arthrobacter sp. MTCC 5214 during solid-state fermentation of wheat bran, was evaluated for prebleaching of kraft pulp. A thermostable alkaline lipase from Arthrobacter sp. BGCC no. 490, which was characterized by high activity in the presence of acetone, isopropanol, ethanol, and methanol, was proposed for applications in the detergent industry.
Biodegradation of Agrochemicals and Pollutants Arthrobacters are capable of participating in the degradation of various compounds deriving from agrochemicals, pharmaceuticals, and toxic wastes, in polluted temperate and cold environments. Polychlorinated phenols such as 4-chlorophenol may be released accidentally into the environment. Arthrobacter ureafaciens degrades 4-chlorophenol through the elimination of the chloro-substituent and the production of the hydroquinone as transient intermediates. Other para-substituted phenols are metabolized through the hydroquinone pathway. Picolinic acid (2-carboxylpyridine), structurally similar to the herbicide picloram (4-amino-3,5,6-trichloropicolinic acid) and the photolytic product of another herbicide, diquat (1,10 dimethyl-4,40 -bipyridylium ion), is used as carbon and energy sources by Arthrobacter picolinophilus. Diazinon O,O-diethyl O-[4-methyl-6-(propan-2-yl)pyrimidin-2-yl] phosphorothioate added to paddy water for controlling stem borer, leafhopper, and planthopper pests of rice is degraded by arthrobacters. One
Arthrobacter isolate from treated paddy water metabolized it in the presence of ethyl alcohol or glucose. Arthrobacter oxydans, isolated from soil, degrades the phenylcarbamate herbicides phenmedipham methyl (3-methylcarbaniloyloxy) carbanilate and desmedipham (3-ethoxycarbonylaminophenyl-phenylcarbamate), by hydrolyzing their central carbamate linkages (carbamate hydrolase). Phenmedipham and desmedipham are hydrolyzed at comparable rates, whereas phenisopham, a compound with an additional alkyl substitution at the carbamate nitrogen, is not hydrolyzed. In some cases, synthetic aromatic compounds, such as m-chlorobenzoate, may account only for incomplete degradation. The benzoate-oxidizing enzyme of Arthrobacter spp. produces 4-chlorocatechol from m-chlorobenzoate, which is not further degraded by catechol-metabolizing enzymes. Cometabolism could result from an accumulation of some toxic product or from an inability of the organism to carry the metabolism to a stage at which the carbon could be assimilated. Arthrobacters would be promising candidates for bioremediation of contaminated soils and water. A biofilter using granular activated carbon with coimmobilized Paracoccus sp. CP2 and Arthrobacter sp. CP1 achieved the complete degradation of trimethylamine, a teratogenic and maleodorous pollutant, which frequently was found in effluents from fishmeal manufacturing process. The ability to degrade trimethylamine also was found in Arthrobacter protophormiae. Arthrobacter sp. strain JBH1 was able to degrade nitroglycerin in soil through a pathway that involves the conversion of nitroglycerin to glycerol, via 1,2-dinitroglycerin and 1-mononitroglycerin, with concomitant release of nitrite. Arthrobacter aurescens strains, which were isolated from contaminated sites and possess atrazine-degrading genes trzN, atzB, and atzC, were capable of degrading atrazine in contaminated soil and wastewater in bioremediation trials. Arthrobacter sp. strain IF1 had the capacity to grow on 4-fluorophenol (4-FP), as the sole source of carbon and energy, through the conversion of 4-FP into hydroquinone via a twocomponent monooxygenase system. Other compounds biodegraded in contaminated soil by Arthrobacter sp. are 4-chlorophenol (Arthrobacter chlorophenolicus, Arthrobacter defluvii sp. nov.), nicotine (Arthrobacter nicotinovorans), 4-nitroguaiacol (Arthrobacter nitroguajacolicus sp. nov.), acrylonitrile (A. nitroguajacolicus sp. nov.), p-nitrophenol (A. chlorophenolicus, A. protophormiae), phenol (A. citreus), imazaquin (A. crystallopoietes), and phthalic acid esters, 4-fluorocinnamic acid, phthalate esters, tris (1,3-dichloro-2-propyl) phosphate, dibenzothiophene, carbazole, quinaldine, and 4-chlorobenzoic acid. Arthrobacters colonize heavy metal–contaminated sites. The multiple metal-resistant Arthrobacter ramosus strain was found to withstand and bioaccumulate several metals, such as cadmium, cobalt, zinc, chromium, and mercury. It may reduce and detoxify redox-active metals, like chromium and mercury. Similar activities were found in A. globiformis. The use of Arthrobacter viscosus and A. aurescens for removing chromium in water and soil was reported. The potential of the chromium reductase of Arthrobacter rhombi to reduce hexavalent chromium (Cr(VI)) was evaluated. The capacity of Arthrobacter sp. to remove Cu2þ ions from aqueous solution also was demonstrated.
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Arthrobacters may contribute significantly to wastewater treatment and groundwater remediation problems because of the accidental release of gasoline in the environment. There are difficulties with the biological treatment of gasoline oxygenates such as methyl t-butyl ether. Ethers tend to be quite resistant to biodegradation by microorganisms. Pure cultures of Arthrobacter spp. are able to degrade methyl t-butyl ether by using it as a carbon source. Phenantrene- and anthracene-degrading strains belonging to Arthrobacter phenanthrenivorans sp. nov. were characterized. Nondegradable and persistent compounds such as plastic, polyethylene, polycarbonate, and polyester pose a threat to the environment. Bacteria may be considered as potent utilizers of these compounds because of their ability to produce various enzymes needed for breakdown of such compounds. In view of these factors, Arthrobacter and Enterobacter strains were used for in vitro biodegradation, showing a significant utilization of polycarbonate.
Involvement in Clinical Specimens Strains of Arthrobacter spp. have been very rarely described as causing disease in humans (case reports described occasional subacuted infective endocarditis, bacteremia, postoperative endophthalmitis, Whipple disease-like syndrome, and phlebitis). In recent years, however, clinical microbiologists have begun to fully recognize the enormous diversities of coryneform bacteria in clinical specimens and a large number of strains isolated in clinical bacteriology laboratories were unambiguously assigned to the Arthrobacter spp. through 16S rDNA gene sequence and peptidoglycan analyses. New species, such as Arthrobacter cumminsii and Arthrobacter woluwensis, were proposed. Arthrobacter cumminsii might be the most frequently encountered Arthrobacter in clinical specimens, because it was isolated from patients with urinary tract and deep tissue infections, and external otitis. Arthrobacter cumminsii seems to be a microorganism with no or rather low pathogenicity as cases of severe, life-threatening infections were not observed in patients. It might be the only bacterial agent for selected cases of urinary tract infections. It is likely that A. cumminsii is part of the normal human skin and mucosa membrane biota, in particular, in the genitourinary tract. Arthrobacter oxydans, Arthrobacter luteolus, Arthrobacter albus, and Arthrobacter scleromae also were isolated from human clinical specimens. Arthrobacter sanguinis and, the creatinehydrolyzing species, Arthrobacter creatinolyticus were isolated from human blood and urine, respectively. The major part of the Arthrobacters isolated from clinical specimens exhibited susceptibility to b-lactams, doxycycline, gentamicin, linezolid, rifampin, and vancomycin. Arthrobacter equi and Arthrobacter nasiphocae were isolated from animal sources (horse and common seal, respectively). Recently, lyophilized Arthrobacter cells were included in a vaccine for treatment or prevention of piscirickettsiosis in salmonid fish.
See also: Brevibacterium; Cheese: Mold-Ripened Varieties; Cheese: Microflora of White-Brined Cheeses; Fish: Spoilage of
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Fish; Spoilage of Meat; Milk and Milk Products: Microbiology of Liquid Milk.
Further Reading Euzéby, J.P., List of Prokaryotic Names with Standing in nomenclature – genus Arthrobacter, www.bacterio.cict.fr. Funke, G., Pagano-Niederer, M., Sjödén, B., Falsen, E., 1998. Characteristics of Arthrobacter cumminsii, the most frequently encountered Arthrobacter species in human clinical specimens. Applied and Environmental Microbiology 36, 1539–1543. Heyrman, J., Verbeeren, J., Schumann, P., Swings, J., De Vos, P., 2005. Six novel Arthrobacter species isolated from deteriorated mural paintings. International Journal of Systematic and Evolutionary Microbiology 55, 1457–1464. Jones, D., Keddie, R.M., 2006. The genus Arthrobacter. Prokariotes 3, 945–960.
Keddie, R.M., Collins, M.D., Jones, D., 1986. Genus arthrobacter conn and dimmick 1947, 300AL. In: Sneath, P.H., Mair, N.S., Sharpe, M.E., Holt, J.G. (Eds.), Genus Arthrobacter, Bergey’s Manual of Systematic Bacteriology, vol. 2. Williams & Wilkins, Baltimore, p. 1288. Koch, C., Rainey, F.H., Stackebrandt, E., 1994. 16S rDNA studies on members of Arthrobacter and Micrococcus: and aid for their future taxonomic restructuring. FEMS Microbiology Letters 123, 167–172. Kolloffel, B., Burri, S., Meile, L., Teuber, M., 1997. Development of 16S rRNA oligonucleotide probes for Brevibacterium, Micrococcus/Arthrobacter and Microbacterium/Aureobacterium used in dairy starter cultures. Systematic and Applied Microbiology 20, 409–417. Mages, I.S., Frodl, R., Bernard, K.A., Funke, G., 2008. Identities of Arthrobacter spp. and Arthrobacter-like bacteria encountered in human clinical specimens. Journal of Clinical Microbiology 46, 2980–2986. Smacchi, E., Fox, P.F., Gobbetti, M., 1999. Purification and characterization of two extracellular proteinase from Arthrobacter nicotianae 9458. FEMS Microbiology Letters 170, 327–333.