Quorum sensing interruption as a tool to control virulence of plant pathogenic bacteria

Physiological and Molecular Plant Pathology 106 (2019) 281–291

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Physiological and Molecular Plant Pathology journal homepage: www.elsevier.com/locate/pmpp

Quorum sensing interruption as a tool to control virulence of plant pathogenic bacteria

T

M.M. Gutiérrez-Pachecoa, A.T. Bernal-Mercadoa, F.J. Vázquez-Armentaa, M.A. Mart ínez-Telleza, G.A. González-Aguilara, J. Lizardi-Mendozaa, T.J. Madera-Santanaa, F. Nazzarob, J.F. Ayala-Zavalaa,∗ a Centro de Investigación en Alimentación y Desarrollo, A.C. (CIAD, AC), Carretera Gustavo Enrique Astiazarán Rosas, N0. 46, La Victoria, Hermosillo, Sonora, 83304, Mexico b ISA CNR, Institute of Food Science, Via Roma 64, 83100, Avellino, Italy

A R T I C LE I N FO

A B S T R A C T

Keywords: Phytopathogen Plant diseases Virulence factors Plant extracts Natural compounds

Pathogenic bacteria use Quorum sensing (QS) to regulate the expression of virulence factors involved in plant tissue infection. Some of these factors are the production of biofilm, hydrolytic enzymes, toxins, and plasmids; therefore, the interruption of this system could be a useful tool to control plant tissue infections. This review analyzes the potential treatments to interrupt QS and control the infection of plant tissues.

1. Introduction Bacterial colonization of plant tissues is a natural phenomenon facilitated by the presence of nutrients, moisture, and pH. As a consequence, bacterial diseases are responsible for considerable losses in many crops, affecting their yield and quality around the world [1]. Ralstonia solanacearum, Pseudomonas syringae, Xanthomonas campestris, Xylella fastidiosa, Dickeya dadantii, and some Pectobacterium species are among the most important plant pathogens in terms of virulence and therefore with economic impact [2]. However, these species are only a small part of the vast number of plant pathogens. When these bacteria grow, in response to increased cell-population density, they activate an intercellular communication mechanism called Quorum sensing (QS). For many bacterial plant pathogens, this system consists of a LuxI type protein that synthesizes the signal molecules to be sensed by a receptor protein; then, the formed adduct will interact with specific DNA sections in the QS regulon to activate the expression of virulence factors [3]. The expressed virulence factors include the production of biofilm, cell wall degrading enzymes (PCWDE), and phytotoxins. Good agricultural practices and the use of conventional antibiotics have been proposed to reduce the incidence of plant bacterial diseases [4,5]. However, bacterial resistance to conventional antibiotics is an international concern; in addition, these agents normally do not affect the expression of virulence factors, instead they attack the cell viability

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and survival microorganisms can develop resistance to future treatments. As alternatives, some plant extracts and their bioactive compounds have shown effectiveness to interrupt QS and reduce the virulence of different Pectobacterium species, R. solanacearum, among others [6,7]. In this sense, the use of phytochemicals has been proposed to disrupt the LuxI/R type QS system and virulence. Therefore, the objective of this review is to analyze the potential of natural compounds as anti-virulence agents due to their capacity to interrupt the QS system of Gram-negative plant pathogenic bacteria. 2. Infectious diseases caused by plant pathogenic bacteria Bacterial contamination of surfaces in contact with plant tissues is a serious problem compromising food production, favoring cross-contamination, and spreading diseases [8,9]. In plants, bacterial colonization is a natural phenomenon occurring in a wide range of conditions like nutrient availability, moisture, and pH near neutral. Plant diseases are responsible for considerable losses in many crops, causing a reduction in the quantity and quality of harvested products. At least 10% of global plant food production is lost due to bacterial diseases acquired at pre- and post-harvest periods. During the pre-harvest, pathogenic bacteria can be established and after, during post-harvest, they can grow and develop the infection [10]. The contamination process has been linked to the use of contaminated water during irrigation [11].

Corresponding author. E-mail address: [email protected] (J.F. Ayala-Zavala).

https://doi.org/10.1016/j.pmpp.2019.04.002 Received 26 February 2019; Received in revised form 1 April 2019; Accepted 3 April 2019 Available online 09 April 2019 0885-5765/ © 2019 Elsevier Ltd. All rights reserved.

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synthesis of exopolysaccharides that reduce the flow of water in the xylem vessels, as well as colonizes fruits, appearing symptoms during their post-harvest storage [34]. In general, the symptoms caused by these pathogens are associated with interference with the plant vital functions including hormone regulation, photosynthesis, reproduction, water uptake and its transport, as well as the quality of their fruits [35]; these infections are facilitated by the expression of virulence factors such as motility, toxin and PCWDE synthesis, SPE production, and biofilm formation.

Table 1 World production and losses of the main staple crops at 2016. Crop

Production (ton)a

Crop losses (%)b

Maize Rice Wheat Potatoes Soybeans Vegetables Sorghum Roots and tubers

1,060,107,470 740,961,445 749,460,077 376,826,967 334,894,085 290,130,864 63,930,558 10,455,162

8.5 10.8 10.2 14.5 8.9 – – –

3. Virulence factors of plant pathogenic bacteria

a

World production of staple crops at 2016 [14]. b Crop losses (%) attributed to plant diseases worldwide between 2001 and 2003 [15]. – non published data were found.

Plants are rich in water and nutrients offering an optimal environment for survival and proliferation of bacteria [36]. Pathogens express several virulence factors that allow their infection cycle. A virulence factor is expressed by a pathogen to influence the vital functions of the host, allowing the pathogen growth and colonization. Their expression occurs via different regulatory networks such as two-component signaltransduction systems, post-transcriptional regulation systems, AraC-like regulators, sigma factors, and the intercellular communication system called QS [37]. QS allows the bacteria to monitor their local population density via the secretion and detection of small diffusible signal molecules. For example, in Gram-negative bacteria the LuxI/LuxR-type QS uses acyl homoserine lactones (AHL) as signal molecules; oligopeptidetwo-component-type in Gram-positive bacteria and the luxS-encoded autoinducer 2 in both Gram-negative and Gram-positive bacteria [38]. However; most of the Gram-negative plant pathogens uses the LuxI/ LuxR QS system in which AHL are synthesized by the cytoplasmic LuxI type proteins (homologous to the Vibrio fisheri protein) with S-adenosyl methionine and acyl-acyl carrier protein as substrates [3]. Once the concentration of the synthesized signal molecules increases at threshold levels, the AHL interacts with the LuxR type receptor proteins to form an active complex with high affinity to specific DNA sequences called “lux boxes”. These sequences are found in the promoter regions of several genes in the QS regulon and activate the expression of their respective virulence factors [39]. However, it is important to highlight that plant pathogens utilize very specific QS systems where the signaling molecules differ not only in the length of the acyl chain and their oxidation state of C3, but also in the respective receptor protein to express particular virulence factors (Table 3). This is the case of X. fastidiosa and some species of Xanthomonas which synthesizes unsaturated fatty acids as signal molecules instead of AHL [3]. Among the virulence factors secreted by plant pathogens include production of phytotoxins, extracellular polymeric substances (EPS), antibiotics against competitive organisms, plasmids, swimming and swarming motility, biofilms, PCWDE, among others. These factors allow the colonization and acquisition of the plant

Also, during post-harvest processing, washing with contaminated water and un-sanitized storage facilities led to the increment of infection due to cross-contamination of contact surfaces like stainless steel, cardboard boxes, and polypropylene crates. In this sense, the infection cycle of plant pathogens can start not only in the field, but also during postharvest handling when the environmental conditions are favorable. Plants account for over 80% of the human diet and are essential to assure food security [12]. So, bacterial plant diseases are a problem to maintain food security, exacerbating the current deficit of food supply [13]. Most humans live on a diet based on staple crops and their production and preservation are compromised. Table 1 lists the significant plant food sources for human nutrition; but concurrently, they are commonly susceptible to several diseases. Today there are no recent statistics reporting the losses of staple crops caused particularly by bacterial diseases; however, this represents a problem considering the past data and the actual international prerogative to assure food security. It has been reported that plant disease caused 20–40% losses of global crop yields [12]. Most bacterial diseases were related to the infection of the Gram-negative bacteria P. syringae, X. campestris, R. solanacearum, Agrobacterium tumefaciens, Xanthomonas oryzae, Pectobacterium amylovorum, X. fastidiosa, D. dadantii, Pectobacterium carotovorum subsp. carotovorum, and subsp. atrosepticum [2]. These pathogens are known to cause different diseases in a wide variety of plants in stem, leaf and fruits (Table 2). For example, P. syringae colonizes bean leaves and promotes the occurrence of brown spot disease causing cell aggregation [33]. A. tumefaciens causes the crown gall tumor, one of the most serious plant diseases worldwide. In nature, this bacterium induces neoplastic growth on the infected plant and reduces vigor and crop yield [2]. On the other hand, R. solanacearum causes a vascular wilt disease on potato, tomato, tobacco, and bananas; which is characterized by the

Table 2 Plant pathogenic bacteria responsible of causing infectious diseases in a wide range of crops and fresh produce. Phytopathogen

Hosts

Disease

Reference

Agrobacterium tumefasciens Burkholderia glumae Candidatus Liberibacter asiaticus Dickeya dadantii Pantoea stewartii Pectobacterium amylovorum Pectobacterium carotovorum Pseudomonas corrugate Pseudomonas fuscovaginae Pseudomonas syringae Ralstonia solanacearum Spiroplasma kunkelii Xanthomonas axonopodis pv. Phaseoli Xanthomonas campestris Xanthomonas oryzae Xylella fastidiosa

Plants Rice Citrus Potato Sweet corn and maize Apple and pear Potato Tomato Rice, wheat, and maize Bean Tomato, potato, tobacco, and eggplant Maize Soybean Cabbage and cruciferous plants Rice Grapevine, citrus, pear, almonds

Crown gall tumors Rice panicle blight Citrus greening disease Black leg Stewart's vascular wilt and leaf blight Fire blight Soft rot Tomato pith necrosis Brown sheath rot Brown spot disease Bacterial wilt Corn stunt disease Bacterial pustule disease Black rot Bacterial blight Pierce disease

Gohlke and Deeken [16] Kim et al. [17] Koh et al. [18] Degefu et al. [19] Koutsoudis et al. [20] Venturi et al. [21]; Koczan et al. [22] Crépin et al. [23] Licciardello et al. [24] Mattiuzzo et al. [25] Quiñones et al. [26] Yang et al. [27] Davis et al. [28] Boulanger et al. [29] von Bodman et al. [3] He et al. [30]; Wang et al. [31] Ionescu et al. [32]

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nutrients to assure bacterial survival. For example, some species of Pectobacterium need to adhere to the plant surfaces and synthetize PCWDE to degrade the cell wall and internalize; however, they wait to reach a high population density and then activate the synthesis of exoenzymes. This strategy is believed to be used to counteract the plant's defense systems [3]. For this reason, several studies have been conducted to characterize the virulence mechanisms of some plant pathogens to identify potential targets to interrupt these processes [36].

Wang et al. [31] von Bodman et al. [3] Vidaver [35]; He et al. [30]

Mattiuzzo et al. [25]

Licciardello et al. [24]

Venturi et al. [21]; Koczan et al. [22] Koutsoudis et al. [20] Nasser et al. [40] Quiñones et al. [26]

Ionescu et al. [32] Gohlke and Deeken [16] Kim et al. [17] Crépin et al. [23]

Reference

M.M. Gutiérrez-Pacheco, et al.

Exopolysaccharide, motility, and biofilm formation Synthesis of endoglucanase, protease, and extracellular polysaccharide xanthan Exopolysaccharide, extracellular enzymes, iron-chelating siderophores, and type III secretion–dependent effectors

The biofilm formation is an important feature of colonization of plant pathogens occurring on both biotic and abiotic surfaces; this provides protection against environmental stresses, antibiotics, among others. Biofilms are communities of microorganisms embedded in an aqueous matrix of EPS produced by individual cells. Commonly, these include a complex matrix of polysaccharides, proteins, glycol-peptides, lipids, lipopolysaccharides, DNA, and other materials to stabilize the biofilm structure and protect cells from environmental conditions [41]. The composition of biofilm matrix varies among microorganisms, having the plant pathogens polysaccharides as the main components. The biofilm formation can be influenced by several factors but, in general, any surface that combines an abundance of moisture and nutrients can be susceptible to the biofilm formation such as plants, fresh produce and food contact surfaces. Biofilm formation process involves five stages: 1) reversible adhesion, 2) irreversible adhesion, 3) microcolonies formation, 4) maturation, and 5) cell dispersion to assure the survival [42]. The initial stage is the adhesion of planktonic cells on the surface; in this satge, bacteria needs to reach the surface helped by different extracellular structures such as flagella, fimbriae type I and IV, and curli, depending the specie. Bacteria can move by different mechanisms, including flagellar swimming, swarming and twitching motility. Flagellar motility provides access to attachment sites and possibly drives the initial bacterial adhesion. It seems that motility helps to counteract the hydrophobic repulsion between bacteria cells and the target surface [43]. Twitching motility conferred by retractable type IV pili is used by Pseudomonas spp. to spread across the surface and form mushroom-like biofilms [44]. It has been reported that the movement and penetration of bacteria across the plant surface are necessary for a successful colonization. For e.g. R. solanacearum uses type IV pili for surface adhesion and twitching motility. Particularly, the type IV pili PilA facilitates polar attachment to plant cells, whereas non-piliated mutants showed reduced virulence with deficiencies in biofilm formation [45]. Type I pili (fimbriae) is another cell superficial structure required for X. fastidiosa to promote biofilm formation, because the fimA mutant is completely deficient to adhere and form biofilms [46]. In general, the movement of bacteria on biotic surfaces favors to enter throughout stomata and wounds, leading a biofilm formation and colonization of vessels, affecting nutrients flow. Bacterial appendices are not the only factors contributing to the adhesion, also the characteristics of biotic and abiotic surfaces become crucial parameters [47]. The adhesion of bacteria to plant surfaces depends on a number of biochemical and physical properties related to the materials involved, including the surface topography and hydrophobicity. Plant surfaces show a topography given by the presence of the cuticle, stomata's, lenticels, and trichomes. In addition, plant surfaces are covered by a cuticle, a hydrophobic material composed mainly of fatty acids, waxes and polysaccharides (cellulose and pectins) [48]. These characteristics conferred a certain hydrophobicity that promotes the bacterial attachment [49]. On the other hand, the characteristics of abiotic surfaces such as surface free energy, surface charge, hydrophobicity, roughness or a conditioning layer influences the adhesion of bacteria to these materials. The secretion of EPS promotes a stronger and irreversible adhesion

PfsI/R, PfvI/R

PhcB/A RpfF/G RpfF/G

Pseudomonas fuscovaginae

Ralstonia solanacearum Xanthomonas campestris Xanthomonas oryzae

C10 and C12-homoserine lactone, 3-oxo-C10 and 3-oxoC12-homoserine lactone 3-hydroxy palmitic acid ester cis-11-methyl-dodecenoic acid, DSF cis, cis-11- methyl-dodeca-2,5-dienoic acid, CDSF

PcoI/R Pseudomonas corrugata

C6-homoserine lactone

Exopolysaccharide synthesis Exoenzyme and exopolysaccharide production Production of exopolysaccharide, elicitors of hypersensitive response, avirulence gene products, plant growth hormones, and phytotoxins Regulation of hypersensitive response, swarming motility, synthesis of phytotoxic, and antimicrobial compounds (corpetin A and B and cormycin) Phytotoxins EsaI/R ExpI/R AhlI/R

Pectobacterium amylovorum

Pantoea stewartii Dickeya dadantii Pseudomonas syringae

3-oxo-C6-homoserine lactone 3-oxo-C6-homoserine lactone 3-oxo-C6-homoserine lactone

Levan synthesis

Twitching motility and biofilm formation Ti plasmid conjugation Toxoflavin, lipase, and type III effectors Exoenzyme and antibiotic production

12-methyl-tetradecanoic acid, DSF 3-oxo-C8-homoserine lactone Octanoyl-homoserine lactone 3-oxo-C6-homoserine lactone, 3-oxo-C8-homoserine lactone 3-oxo-C6-homoserine lactone RpfF/C TraI/R TofI/R ExpI/R, CarI/ R EamI/R Xylella fastidiosa Agrobacterium tumefasciens Burkholderia glumae Pectobacterium carotovorum

QS signal QS system Phytopathogen

Table 3 Virulence of plant pathogenic bacteria, QS systems, signal molecules, and virulence factors.

Virulence factors

3.1. Biofilms

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addition, P. syringae virulence depended on the AhlI/R QS signaling system and mutants impaired for production of alginate were more susceptible to desiccation stress and exhibited different virulence patterns [26]. R. solanacearum synthesizes large amounts of an acidic soluble exopolysaccharide; its massive production during plant infection is associated with the restriction of water flow in xylem vessels, affecting nutrient movement, and causing plant death. In the same bacteria, QS regulates the synthesis of exopolysaccharides and biofilm formation throughout the global virulence regulator PhcA. Particularly, the QS system of this pathogen involves the synthesis of a 3-hydroxy palmitic acid ester (3-OH-PAME) in contrast with other plant pathogens that synthetizes AHL. This bacterium possesses the 3-OH-PAME synthase PhcB, a membrane-bound sensor (PhcS), and a response regulator (PhcR) [60]. At high cell densities, 3-OH-PAME is synthetized and binds to PhcS to release PhcA from repression. Then, PhcA directly or indirectly activates the production of exopolysaccharides in direct or indirect way, contributing to biofilm formation [37]. This information reflects the important role of EPS synthesis and biofilm development for a successful colonization, virulence, and resistance of plant pathogenic bacteria against antibiotics. The studies about biofilms, either human or plant pathogens must be focused on the characterization of the complete process of biofilm formation on plant food and food contact surfaces. This information has been generalized for major pathogens; however, it is well known that this process can change between microorganisms. Some recent studies have evaluated several virulence factors of plant pathogens, but a detailed analysis of their characteristics has not been made [27,61,62]. For example, many of them measure the formation of biofilm as aggregates or biomass, leaving aside that the measurement of biomass (crystal violet) that gives un-specific information about a great diversity of components that make up the biofilm [63]. It is necessary to make a deeper analysis, contemplating this status quo precisely as a multicomponent system in which each of these components greatly influences the characteristics of the virulence [7,64]. In general, the formation of biofilms can be “attacked” by different ways, either inhibiting adhesion processes, changing surface characteristics, inhibiting the synthesis of important flagellar compounds, the same movement of the flagellum, the formation of microcolonies, the QS, the EPS synthesis, or favor the dispersion process by affecting biofilm structural stability, among others (Fig. 1). For example, Athinuwat, et al. [65] reported that the inhibition of the genes flgK and pilD (involved in the regulation of assembly of the monopolar flagellum and type IV pili) resulted in an altered swimming and twitching motility of X. axonopodis pv. glycines. This directly impacts the ability of this pathogen to form biofilms and cause disease in soybean cultivars. However, it is well known that one of the determining factors in the formation of biofilms is the QS, due to its influence on EPS synthesis and even in the activation of genes related to the induction of EPS degrading enzymes in the dispersion process, and others involved in the regulation, maturation, and maintenance of biofilms. So, it is necessary to improve our understanding of the cellular process that controls plant pathogens biofilms to develop approaches for the discovery of disinfectant treatments. In addition to its role in biofilms, the QS controls the production of other virulence factors. Then, the QS inhibitors, in addition to their anti-biofilm activity, can also counteract the bacterial virulence and therefore pathogenicity.

and it occurs during the second step of biofilm development [50]. EPS synthesis is regulated by the QS system in bacteria such as P. stewartii, R. solanacearum, and X. campestris in a different way than other virulence factors in some bacteria [3]. For example, in P. stewartii, the activation of cps genes related with exopolysaccharides synthesis is throughout the repressor activity of EsaR. At low AHL concentrations (low cell density), EsaR works as a DNA binding agent and as a direct repressor of rcsA transcription, obtaining basal levels of RcsA protein which is subjected to degradation by Lon protease, preventing the formation of the RcsA/RcsB complex. Contrarily, at high cell density, the repressor activity of EsaR is affected (due to its binding with AHL), allowing the fast expression of rcsA, and therefore, the levels of RcsA exceed the degradation capacity of Lon. Therefore, RcsA recruit to RcsB to form an activation complex and the activation of cps genes related with exopolysaccharides synthesis [51]. The function of exopolysaccharides is to protect bacterial cells, favor cell-to-cell, and cell-substrate interactions, granting stability to the aggregated. Then, bacterial micro-colonies are established (stage 3 during biofilm development) and they start to grow creating a three-dimensional structure to contain clusters of cells and channels that effectively distribute nutrients and signaling molecules [52]. During stage 4, plant pathogens completely colonize the surface and species such as Pectobacteria can synthesize extracellular enzymes to promote the infection [53]. Finally, in stage 5, biofilm cells are detached to be dispersed and colonize other surfaces [43]. It has been reported that EPS synthesis is the main factor that contributes to biofilm formation. The production of EPS is considered to be an important strategy that contributes significantly to bacterial growth, survival, and virulence [3]. As mentioned before, one bacterial disease symptom is the dysfunction of water uptake and transport; and it is proposed that the secreted bacterial EPS are responsible for this [3]. The expression of the cps gene cluster that encodes EPS synthesis in P. stewartii is regulated by the EsaI/R QS system and mutations in the cpsA-M locus lead to less wilting, thus establishing EPS as a primary virulence factor [54]. On the other hand, von Bodman et al. [3] found that mutations in the AHL synthase encoding gene (expI) eliminated the AHL synthesis and EPS production, which is reflected also in a reduced virulence because this EPS blocks plant xylem vessels and causes wilting. Xanthan gum is the major EPS produced by Xanthomonas spp. and this production is accomplished by a cluster of 12 genes (annotated as gumB through gumM), some of which codify to glucosyltransferases enzymes. In addition, X. campestris strains carrying mutations that specifically disrupt EPS production have reduced virulence [55,56]. In X. oryzae, the QS regulation of EPS and biofilm formation is throughout the biosynthesis of the 12-methyl-tetradecanoic acid (DSF) signal, which is encoded by the pathogenicity factors (rpfABCDEFG) genes. This QS system modulates the levels of a second messenger cyclic diGMP, and this can be found at high concentrations when the cell density is low, and it binds to the transcriptional activator (Clp), disrupting QS. RpfF is in charge of synthesizing DSF signals, but at low cell densities, its catalytic activity is reduced because binds RpfC. However, at high cell densities, RpfC detaches from RpfF and the unbound RpfF catalyzes the production of more DFS signals, which then binds to the phosphorylated RpfC. This phosphorylation leads to a reduction in the levels of cyclic di-GMP and its separation from the Clp activator [57]. Amylovoran is an EPS necessary for biofilm production of P. amylovorum (previously known as Erwinia amylovora) and levan, another EPS, it is considered a stabilizing agent, allowing bacteria to attach to several surfaces, suppress pathogen recognition, cause water-soaking, and collapse plant tissue [22]. The quantity of amylovoran produced by this pathogen has been positively correlated with its virulence [58]. On the other hand, cellulose has been implicated in plant attachment and biofilm formation by different bacteria. Loss of cellulose synthesis in A. tumefaciens resulted in weakened binding to plant surfaces, whereas its over-production resulted in profuse biofilms over plant tissues [59]. In

3.2. Extracellular enzymes as virulence factors Pathogenic bacteria have enzymatic complexes to attack cell walls of leaves, fruits, and vegetables, degrading mainly pectic components to successfully establish an infection. These PCWDE include pectate lyase (Pel), pectin lyase (Pnl), pectin methylesterase (Pme), cellulase (Cel), polygalacturanase (Peh), and proteases (Prt), among others. These are secreted through the Type I (T1SS) (protease) and Type II (T2SS) 284

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Fig. 1. Different targets to be attacked during the biofilm formation process.

three Prt, and one Cel. It has been reported that PecS, a transcriptional regulatory protein, acts as a repressor of their synthesis and it is a complex virulence regulator. PecS directs the production and secretion of PCWDE, as well as the pecS expression that is activated by the QS [70]. On the other hand, PhcA, a Lys-type transcriptional regulator is modulated by the presence of 3-OH-PAME and regulates endoglucanase and Pme production in R. solanacearum. QS in this pathogen drives their transition from the soil to the plant colonization, incrementing levels of 3-OH-PAME to promote the PhcA activity and the expression of exoenzymes. Despite the number of publications about the exoenzyme production by plant pathogens, most of this information is regarding the inhibition of gene expression and synthesis of exoenzymes. As mentioned before, PCWDE are synthesized in the bacterial cell and secreted into the extracellular environment. These systems translocate macromolecules across the cell envelope and in some cases directly into the host. It has been reported that T2SS is required for the secretion of virulence factors of bacterial pathogens such as Klebsiella, P. aeruginosa, Vibrio cholerae, and Pectobacterium species [71]. Specifically, in P. aeruginosa, T2SS has been also involved in the assembly of type IV pili (required for bacterial adhesion and biofilm formation) [72]. The major studies in the field have been conducted with T3SS as targets which are the key virulence factors of many Gram-negative bacteria such as E. coli; however, Pectobacteria and Xanthomonas species among other pathogens secrete virulence factors throughout T1SS and T2SS. For example, Gauthier, et al. [73] reported that compounds such as halogenated salicylaldehyde reduced the amounts of T3SS components inside cells. However, for Yersinia T3SS, salicylidene acylhydrazides was the most active compound to block the T3SS process without affecting transcription of the encoding genes. In this sense, a good strategy to inhibit PCWDE production to combat plant pathogens virulence could be the affectation of the synthesis/function of the secretion system components. If it is considered that the QS controls both the expression and the secretion systems responsible for the release of PCWDE to the extracellular medium, this can be a point of control for this virulence factor.

(pectinases and cellulases) secretion systems to the extracellular environment [66]. The expression and synthesis of the PCWDE are regulated also by the QS [67]. As mentioned above, QS through LuxI/R type proteins controls the expression of several virulence genes, including these enzymes. Previous works deleting the AHL synthase gene (expI) of P. atrosepticum caused lower transcripts abundance of the main PCWDE (pnl, pel, peh, pme, cel and prt) and this was associated with a reduction of the T1SS (prtDEF) expression compared to the wild type [68]. The regulation of PCWDE by QS is throughout different mechanisms in Pectobacteria; for example, the activation of specific transcriptional regulators. In this process, it has been reported that the expression of these regulators is potentiated (e.g. hexA, kdgR, and rsmA) and reduced (expA, expR, virR, etc.) in expI mutants and that these changes affected the production of PCWDE [68]. The production and secretion of the PCWDE are important factors for the virulence of P. carotovorum and P. atroscepticum. These pathogens are known to cause soft rot in many crops, characterized by a tissue maceration attributed to the synthesis of the aforementioned enzymes. The gene expression of PCWDE in Pectobacteria is only activated when high concentrations of AHL have been accumulated. The presence of an elevated concentration of AHL is sensed by the protein ExpR, then the complex AHL-ExpR prevents the transcription of rsmA, which codifies to RsmA (negative regulator), and lets free the mRNA transcripts that encode for PCWDE [37]. Mutants of rsmA overproduce degradative enzymes and are hyper-virulent. Dickeya spp. are plant pathogens that also cause soft rot disease in a wide range of plants and vegetables as a result of the production PCWDE [69]. PCWDE synthesis in Dickeya is regulated by two QS systems: the ExpI/R QS system and the virulence factor modulating (VFM) QS system. In the first, some species like D. dadantii, D. solani, D. chrysanthemi, and D. dianthicola synthetize and sense AHL similarly to P. carotovorum. On the other hand, the second QS system involves the synthesis and perception of VFM, a signal molecule of unknown structure. The vfm cluster consists of four transcriptional units (vfmAZBCD, vfmE, vfmFGHIJ, vfmKLMNOPQRSTUVW) involved in the production of the signal VFM. Among the vfm genes, vfmHI, encoding a two-component regulatory system, seems to be on the top of the hierarchy in signal perception, controlling a second regulatory gene, vfmE, which encodes a transcriptional activator of the AraC family [40]. D. dadantii expI mutants had a greater influence on the virulence and maceration of potato tubers [70]. Particularly, D. dadantii (strain 3937) secretes at least nine endo-Pel and three accessory pectinases,

3.3. Toxins and plasmids Toxins and plasmids are secreted by plant pathogenic bacteria to continue the infection process once they initiated the secretion of 285

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diseased plants) [5]. For this reason, it is necessary to find strategies to control the colonization of food plant tissues and food contact surfaces, as well as the production and activity of virulence factors that contribute to the disease development.

PCWDE or biofilm formation. Plant pathogenic bacteria produce toxins to cause cellular alterations and to influence plant development. These toxins are often identified as the first virulence factors in pathogenesis and they have been studied in depth [74]. Albicidins are phytotoxins synthetized by Xanthomonas albilineans that contribute to the leaf scald disease of sugarcane (Saccharum officinarum L.). On the other hand, P. syringae pv. phaseolicola and P. syringae pv. actinidiae (legume and kiwi pathogens, respectively) synthetizes phaseolotoxin responsible for the appearance of chlorotic zones of the bean halo blight disease. This toxin inhibits ornithine carbamoyl transferase, a critical enzyme in the urea cycle [75]. Some species of Pseudomonas produce toxins such as coronatine, syringomycin, tabtoxin, and phaseolotoxin. In many cases, toxins from P. syringae act as virulence factors, but are not determinant in the disease development [76]; however, in B. glumae toxoflavin is required for the rice grain rot, causing wilt of many field crops. Kim et al. [17] reported that the synthesis of toxoflavin in B. glumae is regulated by QS and activated by ToxJ. TofR forms a complex with C8-AHL at high cell densities and activates toxJ expression and then ToxJ activates the toxABCDE operon, which is responsible for the toxoflavin biosynthesis. This was corroborated with mutants of AHL-synthase, which failed to produce toxoflavin. On the other hand, A. tumefaciens causes crown gall tumors in plants due to its capacity to transfer oncogenic DNA from its tumor-inducing Ti plasmid to the plant; in this bacterium the QS system TraI/R drives the synthesis of the Ti plasmid using the 3-oxo-C8-AHL as autoinducer molecule [16]. TraR–3-oxo-C8-AHL regulates the expression of traI, generating a positive feedback loop. The proposed process to transfer this plasmid to the plant occurs via a type IV secretion system (T4SS), after which TDNA is integrated into the plant host genome. This inter-kingdom DNA transfer leads to overproduction of the plant hormones auxin and cytokinin, resulting in tumors. To date, there is no in-depth study about the toxins of plant pathogens. Although it has been reported that these help to initiate or potentiate the development of the disease, the inhibition of them has not been studied in detail as an alternative inhibiting the virulence of plant pathogens. In this sense some research questions could be detected, is it possible that inhibiting the synthesis of these initiators/ enhancers reduces the virulence or development of diseases caused by the pathogen? The amount of produced toxins is associated with the virulence? Toxins production by itself could directly induce the disease? In this context, P. syringae pv. tobaci infects tobacco leaves and causes small necrotic spot containing bacterial cells, surrounded by a chlorotic zone. This bacteria synthetizes tabtoxin and when tobacco leaves are treated with the isolated toxin, chlorotic spots are observed, suggesting that the formation of disease symptoms by this pathogen is directly correlated to the toxic effect of tabtoxin on plant cells [77]. As observed in the listed evidence, the regulation of the main virulence factors in plant pathogens is given by the QS. Although the majority of pathogens share similarities in their QS systems, their regulation routes show remarkable differences. Some shared key points can be identified among them, such as the synthesis and reception of signal molecules. In this context, the interference with the QS signaling may offer a way of controlling bacterial diseases of plants and crops, as well as to reduce contamination of food contact surfaces. The characterization of the virulence factors could be helpful to integrate the entire picture of this process with the relevance of specific target places for potential anti-virulence agents. This could be relevant since the excessive misuse of antibiotics led to multidrug-resistant strains of bacteria; specifically, QS as a signaling pathway, seems a good target place.

4.1. Traditional management strategies towards virulence of pathogenic plant bacteria Antibiotics and biological control agents have been commonly used to control bacterial plant diseases. Commercially desirable crop varieties often lack genetic resistance to bacterial diseases, and the available antibiotics for use on plants are limited mostly to copper compounds, and few crops to streptomycin, oxytetracycline, gentamicin, oxolinic acid, and kasugamycin [78]. Normally, antibiotics are microbial toxins used to kill other microorganisms even at low doses [1]. These compounds have been shown to be particularly effective suppressing the viability of plant pathogens and their infection. It was estimated that only in the USA in 2011, 36 metric tons of antibiotics were applied to crops [78]. However, there is a global concern in the bacteria resistant to the antibiotic treatments. Streptomycin and oxytetracycline are the main compounds used for the control of some bacterial diseases of plants that can be found in several commercial products around the world. The use of streptomycin is permitted on 12 plant species, some of which include apple, pear, and related ornamental trees for the control of fire blight caused by P. amylovorum. This compound is the antibiotic of election to kill pathogens; however, its mode of action is directed to inhibit only planktonic cell growth, but it does not affect biofilm established populations [4]. Gentamicin is another antibiotic used to control fire blight of apple and pear, and in Latin American countries is used for bacterial diseases caused by species of Pseudomonas, Ralstonia, and Xanthomonas. The resistance of plant pathogens to oxytetracycline is rare, but the emergence of streptomycin-resistant strains of P. amylovorum, Pseudomonas spp., and X. campestris has impeded the control of several important diseases and it is a call to look for alternatives [4]. There are several commercial bactericides used for plant disease control; for example, in Mexico Cuprimicin 100 hyper is a product that combines streptomycin sulfate and oxytetracycline hydrochloride: given their characteristics, these two molecules act inhibiting protein synthesis at ribosomal level. It is particularly effective against P. carotovorum, A. tumefasciens, Corynebacterium sp., C. michiganensis, and X. vesicatoria, among others [79]. Similarly, Agry-gent plus 800 is composed by the same antibiotics and it is a systemic bactericide which penetrates the plant through the stomata and controls a broad spectrum of bacteria such as those that produce rots and/or wilting [80]. On the other hand, Suregold is a fungicide and bactericide of the cupric group that acts on several stages of pathogen growth and disease development. This is composed of copper sulfate pentahydrate, which is absorbed by the plant and acts damaging its cell wall, stopping its multiplication [81]. However, some of them have a extended residual effect which could cause resistance of the survival pathogens. To date, only a few studies reported the anti-QS activity of antibiotics; this is the case of Deryabin and Inchagova [82] who reported that aminoglycosides (gentamycin, kanamycin, and amikacin) inhibited QS system of Chromobacterium violaceum by suppressing C6-AHL production. Major studies in the field have been focused in their combination with known QS inhibitors; however, the used antibiotics only act on the pre-treated bacteria by QS inhibitors and did not act directly on QS [83,84]. In this sense, the information about the effect of antibiotics on the QS is scarce. Because the concerns of antibiotic resistance and actual regulations restricting the use of pesticide, the strategies have been focused on the biological control of plant diseases. The biological control consists in the use of microorganisms capable to suppress the disease and the pathogen viability. This is caused by the synthesis of antibiotics, lytic enzymes, and synthesis of exudates, among others, that affect the

4. Strategies to attenuate the virulence of plant pathogens The control of plant diseases depends on several factors such as the host resistance, the sanitization process (cross-contamination), and cultural practices (preventing the introduction of pathogens, removing 286

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growth of pathogenic bacteria [4]. For example, P. fluorescens is used as biological control because it competes with the pathogen for nutrients and space; unlike antibiotics, which can lose their effectiveness with time, biocontrol bacteria can multiply and persist [5]. Other biological control bacteria include Pantoea agglomerans, Burkholderia cepacia, B. subtilis, etc. Some reports have evidenced the “eavesdropping” capacity of bacteria; which allow them to intercept signal molecules of neighboring microorganisms, provide them of important information about the local environment and other rival species. This cross-talk communication is used by some bacteria as a “competition mechanism” because the interception and sense of these signal molecules could activate the synthesis of molecules capable to inhibit the growth, metabolism or virulence of the other. Both examples of this are the human pathogens Escherichia coli and Salmonella spp., which don't synthesizes AHL but are capable of sense signals generated by other species. This is possible because these bacteria possesses a LuxR homologue called SdiA that responds to exogenous AHL and regulate genes involved in resistance, amino acid transport, metabolism, and transcriptional regulation [85,86]. Besides there are no many studies about “eavesdropping” of biocontrol agents, it is possible to hypothesizes that if these agents have similar QS systems to those of plant pathogens, they can eavesdrop their signals and synthesize higher amounts of virulence factors to attack the other bacteria. For example, the biocontrol agent P. fluorescens 2P24, isolated from wheat roots produces the secondary metabolites 2,4diacetylphloroglucinol (2,4-DAPG), siderophores and hydrogen cyanide, which help to protects tomato from bacterial wilt caused by R. solanacearum. P. fluorescens possess the PcoI/R QS system which synthesizes and sense 3-oxo-AHL, which regulates functions contributing to their biocontrol activities [87]. So, it is possible that in presence of other bacteria that also produced this signal molecule, their biocontrol capacity increase. However, the use of biocontrols has not been completely effective for the control of plant pathogens because it needs to be in contact with the pathogen, and high counts of viable cells to assure the production of effective concentrations of the antibiotics. In this sense, research on other anti-QS agents has been conducted to find more effective and environmentally friendly compounds.

bacteria. 4.2. 1. Phenolic compounds Phenolic compounds are broadly distributed in plants and play a key role as defense responses during infection. In this sense, some investigations have focused on the use of phenolic compounds obtained from plant materials to suppress virulence mainly in human and few in plant pathogenic bacteria. It has been reported that the flavonoids synthesized by tomato plants after P. syringae infection reduced the bacteria motility causing a loss of flagella and expression of a functional type III secretion system [91]. For example, chesnut honey and their aqueous extract at 200 mg/mL significantly reduced the biofilm formation of P. carotovorum by 53.2 and 66.4%, respectively. In addition, this concentration reduced the 3-oxo-C6-AHL production by 45–50% [92]. Lemos et al. [93] reported that ferulic and salicylic acid reduced swimming motility at concentrations of 0.5 mg/mL; whereas salicylic acid was capable to act as QS inhibitor at concentrations of 0.5 and 1 mg/mL. Similarly, Lagonenko, et al. [94] reported that salicylic acid inhibited biofilm formation, motility, and AHL production of P. carotovorum and P. syringae at concentrations of 25 and 50 mM. It was hypothesized that the inhibitory effect of salicylic acid on virulence factors of plant pathogenic bacteria is due to its molecular similarity to the LuxR ligand. In addition, the lower concentration of AHL was explained by the fact that LuxR-like receptor up-regulated the luxI gene expression. However, besides the observed reduction in the AHL, no studies were performed to see if effectively salicylic acid affects the receptor protein or the synthesis of signal molecules. On the other hand, the hydroxycoumarins daphnetin, esculetin, and umbelliferone at 0.1 mg/mL significantly reduced the biofilm formation of R. solanacearum by 99.22%, 93.90%, and 85.20%, respectively. In addition, swimming motility as well as the flagellar genes fliA, flhC, and flhD were significantly repressed by these compounds [27]. These authors reported that the molecular mechanism of biofilm inhibition is related to the down-regulation of flagellar genes (fliA and flhC). However, it is possible that an affectation of secretion systems could be implicated because it has been reported that an alteration of T6SS reduced biofilm formation, motility, and also the expression of the flagella regulon (including fliA and flhC) [95]. p-coumaric acid at 100 μM affected the T3SS gene expression of the plant pathogen D. dadantii. This suggests that plant tissue can also respond to bacterial pathogens by manipulating the expression of the T3SS [96]. As previously mentioned, these secretion systems are used by the pathogens to export different virulence factors to the environment as well as into their hosts. On the other hand, ellagic acid (0.004 mg/mL), pomegranate extract (0.02 mg/mL), and resveratrol (0.02 mg/mL) caused an inhibition of 40–60% of C6-AHL synthesis in P. carotovorum. In addition, it was found that these compounds inhibited violacein production by 85.86, 76.72, and 97.98% in the biosensor strain C. violaceum, respectively. In addition, resveratrol was the most effective in reducing C6-AHL concentration by 81.53% [97]. Similarly, resveratrol (0.008–0.064 mg/mL) and coumarin (0.032 and 0.064 mg/mL) caused a strong inhibition of the swarming motility of R. solanacearum. In addition, biofilm formation was completely inhibited by resveratrol at the lowest dose (0.008 mg/mL), which was reflected in a lower capacity to infect tobacco roots [98]. Joshi et al. [61] reported that cinnamic (0.25 mg/mL) and salicylic acid (0.21 mg/mL) inhibited the expression of QS genes (expI and expR), reduced the level of the AHL signal and down-regulated pecS, pel, and peh genes involved in PCWDE synthesis. Some studies evaluated the anti-QS activity of phenolic compounds by measuring the violacein production by C. violaceum; however, this shows information about the potential anti-QS activity towards a model bacteria and not the problem-related pathogen.

4.2. Plant extracts and their main compounds attenuate virulence of plant pathogenic bacteria Plant compounds are being extensively studied due to its capacity to affect the virulence of human pathogens [64,88]; however, scarce research has been conducted in terms of plant pathogens. It is interesting to note that the use of plant compounds has attracted attention since ancient times to control human pathogenic bacteria and now they are being considered as an option to counteract their antibiotic resistance [89]. In this sense, it seems relevant to conduct studies towards the effect of natural compounds on plant pathogens virulence. Among natural entities, several medicinal plants, herbs, and spices, and their main constituents have been reported to act as QS inhibitory agents, resulting in an inhibition of motility, adhesion, EPS, toxins synthesis, and biofilm formation of plant pathogenic bacteria [7,64,88]. It has been reported that these compounds usually target different points of the bacterial QS (Fig. 2). Remembering and focusing on the importance of the complex AHLQS, and that the signal is synthesized by an AHL synthase, which uses SAM and the acyl-acyl-carrier protein as substrates, several compounds have been directed to interfere with the recognition of the substrate by the enzyme. On the other hand, many natural compounds have shown a high molecular similarity with AHLs which could mimic the interaction of the AHL with its receptor protein, inhibiting its interaction with the DNA [90]. Despite a large number of investigations about the potential of plant extracts to inhibit these processes, little research has been conducted to study the effect of these extracts on plant pathogenic

4.2. 2. Plant essential oils and their main constituents Few reports have been focused on the potential of plant essential 287

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Fig. 2. Natural compounds extracted from plant tissues showed diverse chemical structures that allow them to inhibit QS of plant pathogenic bacteria by different routes: inhibition of QS signal, QS signal precursors, gene expression of QS proteins, and signal reception.

reported that some plant compounds, due to their molecular characteristics, such as amphipathicity, can interact with proteins through hydrophobic interactions or hydrogen bonds [100]. There are various ways by which a compound of this nature could interact with these proteins: interaction with the active site or elsewhere in the protein structure that can cause structural changes and affect its function. P. aeruginosa AHL synthase (LasI) showed two binding pockets in their active site: an S-adenosyl methionine binding site (Phe27, Arg30, and Trp33) and an acyl-acyl-ACP binding site (Arg30, Trp 69, Leu 102, Phe105, Met 125, Leu 140, Thr144, Val 148, Met 151, Met 152, Ala 155, Leu 157, Ile 178, and Leu 188). As observed, the acyl chain binding site is hydrophobic, so, it is possible that the essential oil components can interact on this site, affecting signal synthesis. The correct orientation of these substrates leads to the enzymatic reaction [101]. In this sense, the presence of some natural compounds in these sites could interrupt substrate union and the consequent AHL synthesis. On the other hand, it has been reported that phenolic compounds and EO components could mimic AHLs and be sensed by the LuxR proteins affecting gene translation of virulence factors [88]. Some studies had proposed an approach to the possible mechanism of action of natural compounds to inhibit QS. Such is the case of TapiaRodriguez et al. [88] who reported that carvacrol, the main component of oregano essential oil, down-regulated the expression of the lasR gene of P. aeruginosa. However, this effect was not observed for the protein synthase (LasI), where a possible post-translational effect was proposed, affecting the AHL synthesis. The major studies that directly evaluated the effect of these compounds in the QS system and the subsequent virulence were proved mainly on human pathogenic bacteria; however, few studies include the effect against plant pathogens. This is the case of Joshi et al. [62] who reported that the possible mechanism by which carvacrol and eugenol interrupts QS of P. carotovorum subsp. brasilense and P. atroscepticum is throughout an affectation of ExpI/ExpR proteins; this hypothesis was established only based on the effect of carvacrol on the reduction of AHL synthesis, gene expression, docking analysis, among others; however, the real interaction between these compounds with the protein were not achieved. Chung et al. [102] reported that the synthetic compound J8-C8 (N(3-oxocyclohex-1-enyl) octanamide) inhibited AHL synthesis due to its capacity to interact with the synthase protein TofI of the plant pathogen B. glumae. X-ray crystal structure analysis showed that this compound binds to TofI and occupies the binding site for the acyl-ACP. This compound is structurally similar to several EO components such as

oils (EOs) and their main constituents to inhibit QS mechanisms and virulence factors of plant pathogenic bacteria. Cinnamon, lavender, eucalyptus, and thyme EOs (0.25–1 ppm) caused a significant reduction in biofilm formation of R. solanacearum, being thyme EO (1 ppm) which caused a 23-fold decrease compared to the control [6]. Also, these EOs affected swimming, swarming and twitching motility. It is well known that R. solanacearum uses motility to effectively invade host plants and in this sense, it was concluded that these EOs reduced the pathogenicity of R. solanacearum throughout a motility inhibition. Gutierrez-Pacheco et al. [7] reported that carvacrol, main terpene of oregano essential oil reduced motility (48.2 mm reduction) of P. carotovorum at a concentration of 0.66 mM and was able to reduce EPS synthesis and biofilm formation (1.1 log CFU/cm2) on polypropylene surfaces at 48 h of incubation at 28 °C. Cinnamaldehyde, the main terpene of cinnamon EO reduced the concentration of C6-AHL in P. carotovorum at concentration of 0.05 mg/mL [97]. On the other hand, Joshi, et al. [62] evaluated the effect of carvacrol and eugenol (main compounds of oregano EO) (250 μM) on P. carotovorum subsp. brasilense and showed that these compounds specifically interfere with the QS, resulting in strong inhibition of expI and expR, biofilm formation, and gene expression of PCWDEs (pel, peh, prt), reducing the infection of plant tissues. Zhang et al. [99] reported that carvone, carvacrol, citral, geraniol, thymol, eugenol, and cinamaldehyde at concentrations of 0.1 mg/mL significantly inhibited the motility (swimming, swarming, and twitching), EPS synthesis, and biofilm formation of P. carotovorum. Thymol was the most effective against biofilm formation (47.24%), swimming, swarming, and twitching motility (90–100%). In addition, these authors hypothesized that this effect could be attributed to a QS inhibition due to the reduction of violacein synthesis in the biosensor strain C. violaceum (CV026) after exposure to the terpenoids. The mechanisms proposed by these natural compounds have been related to an inhibition of QS machinery, throughout an inhibition of the signal synthesis, reception, gene expression, and a direct interaction with the signal molecule. However, these compounds must have certain characteristics to exert their action as QS inhibitors: adequate size (if the site of union is a cavity or has a particular conformation) and particular structural characteristics (hydrophobicity, presence of polar groups, and chains of hydrocarbons that allow them to interact and/or reach that site). It is well known that in most Gram-negative bacteria, the QS synthase and receptor proteins are found in the cytoplasm. So, the potential inhibitory compounds must have a certain size and polarity to cross and interact with these proteins. Also, it has been 288

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carvacrol, cinnamaldehyde, and eugenol. In this sense, it is possible an interaction between these compounds and AHL synthase proteins. Docking analysis evidenced that trans-cinnamaldehyde interacts with Phe27 and Trp33 of AHL synthase and form a hydrogen bond with Arg30 [100]. These residues are conserved between the LuxI family, suggesting that similar molecules could interact with other AHL synthases of plant pathogens. Trans-cinnamaldehyde forms hydrophobic and Pi-Pi interactions with the conserved LasI Phe105 located in the open hydrophobic tunnel; whereas in EsaI (from P. stewartii), two hydrogen bonds are formed with Arg 100 and Phe 101 [100]. These interactions between trans-cinnamaldehyde and AHL synthase could affect the recognition of acyl-chain substrate in the catalytic site and inhibit enzymatic activity. To date no binding studies between plant compounds and purified QS proteins of these plant pathogens are provided to evidence the real interaction with these natural inhibitors. The major studies in this field proved the anti-QS activity of plant compounds based on their capacity to affect the virulence of biosensor strains that have a particular phenotype such as luminescence (Escherichia coli pSB401), β-galactosidase activity (A. tumefaciens NT1, A. tumefaciens A136), and violacein production (C. violaceum CV026), among others. However, these sometimes showed limitation because the phenotype is often codependent of other factors and the metabolic activity of the cells and the systems are not the plant pathogenic bacteria [103]. Even when there are some studies of the effect of plant compounds on the QS, a deeper approach of the possible mechanism of action is needed to analyze the direct interaction of the potential inhibitors, an integral analysis of the different points of action, and their potential to attenuate the virulence of plant pathogens in plant models. All this can result in a broader picture of the potential of natural compounds to attenuate the QS as a new strategy to control plant diseases and the contamination of biotic and abiotic surfaces.

[8] [9]

[10] [11]

[12]

[13] [14] [15] [16] [17]

[18]

[19]

[20]

[21]

[22]

5. Conclusion

[23]

The knowledge about the potential of plant extracts and their main compounds to inhibit intercellular communication systems such as QS, opens the door to new possibilities for friendly environmental compounds able to reduce the virulence of plant pathogens and the contamination of biotic and abiotic surfaces. With this in mind and knowing the mechanism by which bacteria regulate their virulence it is possible to propose phenolic and terpenoid compounds as new therapies against infection diseases during pre-harvest and post-harvest contamination of plant foods.

[24]

[25]

[26]

Declarations of interest [27]

None. [28]

References [1] K.K. Pal, B.M. Gardener, Biological control of plant pathogens, The plant health instructor 2 (2006) 1117–1142. [2] J. Mansfield, S. Genin, S. Magori, V. Citovsky, M. Sriariyanum, P. Ronald, M. Dow, V. Verdier, S.V. Beer, M.A. Machado, Top 10 plant pathogenic bacteria in molecular plant pathology, Mol. Plant Pathol. 13 (6) (2012) 614–629. [3] S.B. von Bodman, W.D. Bauer, D.L. Coplin, Quorum sensing in plant-pathogenic bacteria, Annu. Rev. Phytopathol. 41 (1) (2003) 455–482. [4] P.S. McManus, V.O. Stockwell, G.W. Sundin, A.L. Jones, Antibiotic use in plant agriculture, Annu. Rev. Phytopathol. 40 (1) (2002) 443–465. [5] P. McManus, V. Stockwell, Antibiotics for Plant Diseases Control: Silver Bullets or Rusty Sabers, The American Phytopathological Society. APSnet Features, 2000, https://www.researchgate.net/publication/272982829_Antibiotics_for_Plant_ Diseases_Control_Silver_Bullets_or_Rusty_Sabers , Accessed date: 9 April 2019. [6] S. Hosseinzadeh, M. Shams-Bakhsh, E. Hosseinzadeh, Effects of sub-bactericidal concentration of plant essential oils on pathogenicity factors of Ralstonia solanacearum, Arch. Phytopathol. Plant Prot. 46 (6) (2013) 643–655. [7] M. Gutierrez-Pacheco, G. Gonzalez-Aguilar, M. Martinez-Tellez, J. LizardiMendoza, T. Madera-Santana, A. Bernal-Mercado, F. Vazquez-Armenta, J. AyalaZavala, Carvacrol inhibits biofilm formation and production of extracellular

[29]

[30]

[31]

[32]

[33] [34]

289

polymeric substances of Pectobacterium carotovorum subsp. carotovorum, Food Control 89 (2018) 210–218. R. Van Houdt, C.W. Michiels, Biofilm formation and the food industry, a focus on the bacterial outer surface, J. Appl. Microbiol. 109 (4) (2010) 1117–1131. S. Stepanović, I. Ćirković, L. Ranin, M. S✓ vabić‐Vlahović, Biofilm formation by Salmonella spp. and Listeria monocytogenes on plastic surface, Lett. Appl. Microbiol. 38 (5) (2004) 428–432. A. Din, S. Parveen, M.A. Ali, A. Salam, Safety issues in fresh fruits and vegetables-A review, Pakistan J. Food Sci. 21 (1–4) (2011) 1–6. A.J. Hamilton, F. Stagnitti, R. Premier, A.-M. Boland, G. Hale, Quantitative microbial risk assessment models for consumption of raw vegetables irrigated with reclaimed water, Appl. Environ. Microbiol. 72 (5) (2006) 3284–3290. FAO, Keeping Plant Pests and Diseases at Bay: Experts Focus on Global Measures, (2015) http://www.fao.org/news/story/en/item/280489/icode/ , Accessed date: 9 April 2019. R.N. Strange, P.R. Scott, Plant disease: a threat to global food security, Annu. Rev. Phytopathol. 43 (2005) 83–116. FAOSTAT, Production Indices, (2016) http://www.fao.org/faostat/en/#data/QI , Accessed date: 1 September 2018. E.-C. Oerke, Crop losses to pests, J. Agric. Sci. 144 (1) (2006) 31–43. J. Gohlke, R. Deeken, Plant responses to Agrobacterium tumefaciens and crown gall development, Front. Plant Sci. 5 (2014) 155. J. Kim, J.G. Kim, Y. Kang, J.Y. Jang, G.J. Jog, J.Y. Lim, S. Kim, H. Suga, T. Nagamatsu, I. Hwang, Quorum sensing and the LysR‐type transcriptional activator ToxR regulate toxoflavin biosynthesis and transport in Burkholderia glumae, Mol. Microbiol. 54 (4) (2004) 921–934. E.-J. Koh, L. Zhou, D.S. Williams, J. Park, N. Ding, Y.-P. Duan, B.-H. Kang, Callose deposition in the phloem plasmodesmata and inhibition of phloem transport in citrus leaves infected with “Candidatus Liberibacter asiaticus”, Protoplasma 249 (3) (2012) 687–697. Y. Degefu, M. Potrykus, M. Golanowska, E. Virtanen, E. Lojkowska, A new clade of Dickeya spp. plays a major role in potato blackleg outbreaks in North Finland, Ann. Appl. Biol. 162 (2) (2013) 231–241. M.D. Koutsoudis, D. Tsaltas, T.D. Minogue, S.B. von Bodman, Quorum-sensing regulation governs bacterial adhesion, biofilm development, and host colonization in Pantoea stewartii subspecies stewartii, Proc. Natl. Acad. Sci. Unit. States Am. 103 (15) (2006) 5983–5988. V. Venturi, C. Venuti, G. Devescovi, C. Lucchese, A. Friscina, G. Degrassi, C. Aguilar, U. Mazzucchi, The plant pathogen Erwinia amylovora produces acylhomoserine lactone signal molecules in vitro and in planta, FEMS Microbiol. Lett. 241 (2) (2004) 179–183. J.M. Koczan, M.J. McGrath, Y. Zhao, G.W. Sundin, Contribution of Erwinia amylovora exopolysaccharides amylovoran and levan to biofilm formation: implications in pathogenicity, Phytopathology 99 (11) (2009) 1237–1244. A. Crépin, A. Beury-Cirou, C. Barbey, C. Farmer, V. Hélias, J.-F. Burini, D. Faure, X. Latour, N-acyl homoserine lactones in diverse Pectobacterium and Dickeya plant pathogens: diversity, abundance, and involvement in virulence, Sensors 12 (3) (2012) 3484–3497. G. Licciardello, I. Bertani, L. Steindler, P. Bella, V. Venturi, V. Catara, Pseudomonas corrugata contains a conserved N-acyl homoserine lactone Quorum Sensing system; its role in tomato pathogenicity and tobacco hypersensitivity response, FEMS Microbiol. Ecol. 61 (2) (2007) 222–234. M. Mattiuzzo, I. Bertani, S. Ferluga, L. Cabrio, J. Bigirimana, C. Guarnaccia, S. Pongor, H. Maraite, V. Venturi, The plant pathogen Pseudomonas fuscovaginae contains two conserved Quorum Sensing systems involved in virulence and negatively regulated by RsaL and the novel regulator RsaM, Environ. Microbiol. 13 (1) (2011) 145–162. B. Quiñones, G. Dulla, S.E. Lindow, Quorum Sensing regulates exopolysaccharide production, motility, and virulence in Pseudomonas syringae, Mol. Plant Microbe Interact. 18 (7) (2005) 682–693. L. Yang, W. Ding, Y. Xu, D. Wu, S. Li, J. Chen, B. Guo, New insights into the antibacterial activity of hydroxycoumarins against Ralstonia solanacearum, Molecules 21 (4) (2016) 468. R.E. Davis, J. Shao, E.L. Dally, Y. Zhao, G.E. Gasparich, B.J. Gaynor, J.C. Athey, N.A. Harrison, N. Donofrio, Complete genome sequence of Spiroplasma kunkelii strain CR2-3x, causal agent of corn stunt disease in Zea mays L, Genome Announc. 3 (5) (2015) e01216-15. A. Boulanger, T. Boureau, S. Carrere, S. Cesbron, N.W. Chen, S. Cociancich, A. Darrasse, N. Denancé, M. Fischer-Le Saux, L. Gagnevin, Using ecology, physiology, and genomics to understand host specificity in Xanthomonas: French network on, Annu. Rev. Phytopathol. 54 (2016) 6.1–6.25. Y.-W. He, J.e. Wu, J.-S. Cha, L.-H. Zhang, Rice bacterial blight pathogen Xanthomonas oryzae pv. oryzae produces multiple DSF-family signals in regulation of virulence factor production, BMC Microbiol. 10 (1) (2010) 187. X.-Y. Wang, L. Zhou, J. Yang, G.-H. Ji, Y.-W. He, The RpfB-dependent Quorum Sensing signal turnover system is required for adaptation and virulence in rice bacterial blight pathogen Xanthomonas oryzae pv. oryzae, Mol. Plant Microbe Interact. 29 (3) (2016) 220–230. M. Ionescu, C. Baccari, A.M. Da Silva, A. Garcia, K. Yokota, S.E. Lindow, Diffusible Signal Factor (DSF) Synthase RpfF of Xylella fastidiosa is a multifunction protein also required for response to DSF, J. Bacteriol. 195 (23) (2013) 5273–5284. T. Danhorn, C. Fuqua, Biofilm formation by plant-associated bacteria, Annu. Rev. Microbiol. 61 (2007) 401–422. J.S. Kumar, S. Umesha, K.S. Prasad, P. Niranjana, Detection of Quorum Sensing molecules and biofilm formation in Ralstonia solanacearum, Curr. Microbiol. 72 (3) (2016) 297–305.

Physiological and Molecular Plant Pathology 106 (2019) 281–291

M.M. Gutiérrez-Pacheco, et al.

[35] A.K. Vidaver, Phytopathology, Encyclopedia of Life Sciences, John Wiley & Sons, 2001. [36] E.B. Speth, Y.N. Lee, S.Y. He, Pathogen virulence factors as molecular probes of basic plant cellular functions, Curr. Opin. Plant Biol. 10 (6) (2007) 580–586. [37] B.M. Mole, D.A. Baltrus, J.L. Dangl, S.R. Grant, Global virulence regulation networks in phytopathogenic bacteria, Trends Microbiol. 15 (8) (2007) 363–371. [38] Y.-H. Li, X. Tian, Quorum Sensing and bacterial social interactions in biofilms, Sensors 12 (3) (2012) 2519–2538. [39] S.T. Rutherford, B.L. Bassler, Bacterial Quorum Sensing: its role in virulence and possibilities for its control, Cold Spring Harbor perspectives in medicine 2 (11) (2012) a012427. [40] W. Nasser, C. Dorel, J. Wawrzyniak, F. Van Gijsegem, M.C. Groleau, E. Déziel, S. Reverchon, Vfm a new Quorum Sensing system controls the virulence of Dickeya dadantii, Environ. Microbiol. 15 (3) (2013) 865–880. [41] H.-C. Flemming, J. Wingender, The biofilm matrix, Nat. Rev. Microbiol. 8 (9) (2010) 623. [42] P. Stoodley, K. Sauer, D.G. Davies, J.W. Costerton, Biofilms as complex differentiated communities, Annu. Rev. Microbiol. 56 (1) (2002) 187–209. [43] I. Lasa, J. Del Pozo, J.R. Penadés, J. Leiva, Biofilms bacterianos e infección, Anales del Sistema Sanitario de Navarra, SciELO Espana, 2005, pp. 163–175. [44] M. Klausen, A. Heydorn, P. Ragas, L. Lambertsen, A. Aaes‐Jørgensen, S. Molin, T. Tolker‐Nielsen, Biofilm formation by Pseudomonas aeruginosa wild type, flagella and type IV pili mutants, Mol. Microbiol. 48 (6) (2003) 1511–1524. [45] Y. Kang, H. Liu, S. Genin, M.A. Schell, T.P. Denny, Ralstonia solanacearum requires type 4 pili to adhere to multiple surfaces and for natural transformation and virulence, Mol. Microbiol. 46 (2) (2002) 427–437. [46] Y. Meng, Y. Li, C.D. Galvani, G. Hao, J.N. Turner, T.J. Burr, H. Hoch, Upstream migration of Xylella fastidiosa via pilus-driven twitching motility, J. Bacteriol. 187 (16) (2005) 5560–5567. [47] L. Boulangé‐Petermann, J. Rault, M.N. Bellon‐Fontaine, Adhesion of Streptococcus thermophilus to stainless steel with different surface topography and roughness, Biofouling 11 (3) (1997) 201–216. [48] S. Yaron, U. Römling, Biofilm formation by enteric pathogens and its role in plant colonization and persistence, Microbial biotechnology 7 (6) (2014) 496–516. [49] A.G. Torres, C. Jeter, W. Langley, A.G. Matthysse, Differential binding of Escherichia coli O157: H7 to alfalfa, human epithelial cells, and plastic is mediated by a variety of surface structures, Appl. Environ. Microbiol. 71 (12) (2005) 8008–8015. [50] K. Czaczyk, K. Myszka, Biosynthesis of extracellular polymeric substances (EPS) and its role in microbial biofilm formation, Pol. J. Environ. Stud. 16 (6) (2007). [51] T.D. Minogue, A.L. Carlier, M.D. Koutsoudis, S.B. Von Bodman, The cell density‐dependent expression of stewartan exopolysaccharide in Pantoea stewartii ssp. stewartii is a function of EsaR‐mediated repression of the rcsA gene, Mol. Microbiol. 56 (1) (2005) 189–203. [52] S. Srey, I.K. Jahid, S.-D. Ha, Biofilm formation in food industries: a food safety concern, Food Control 31 (2) (2013) 572–585. [53] L. Hall-Stoodley, J.W. Costerton, P. Stoodley, Bacterial biofilms: from the natural environment to infectious diseases, Nat. Rev. Microbiol. 2 (2) (2004) 95–108. [54] R. Chug, B. Khosla, M. Singh, Modulation of the extracellular polymeric substances (EPS) production by Quorum Sensing (QS) in bacteria, Int. J. Curr. Microbiol. App. Sci 4 (6) (2015) 884–896. [55] F.-J. Vorhölter, S. Schneiker, A. Goesmann, L. Krause, T. Bekel, O. Kaiser, B. Linke, T. Patschkowski, C. Rückert, J. Schmid, The genome of Xanthomonas campestris pv. campestris B100 and its use for the reconstruction of metabolic pathways involved in xanthan biosynthesis, J. Biotechnol. 134 (1–2) (2008) 33–45. [56] J.M. Dow, L. Crossman, K. Findlay, Y.-Q. He, J.-X. Feng, J.-L. Tang, Biofilm dispersal in Xanthomonas campestris is controlled by cell–cell signaling and is required for full virulence to plants, Proc. Natl. Acad. Sci. Unit. States Am. 100 (19) (2003) 10995–11000. [57] S. Sibanda, L.N. Moleleki, D.Y. Shyntum, T.A. Coutinho, Quorum Sensing in gramnegative plant pathogenic bacteria, in: J.N. Kimatu (Ed.), Advances in Plant Pathology, IntechOpen, London, 2018, pp. 67–89. [58] M. Maes, K. Orye, S. Bobev, B. Devreese, J. Van Beeumen, A. De Bruyn, R. Busson, P. Herdewijn, K. Morreel, E. Messens, Influence of amylovoran production on virulence of Erwinia amylovora and a different amylovoran structure in E. amylovora isolates from Rubus, Eur. J. Plant Pathol. 107 (8) (2001) 839–844. [59] A.G. Matthysse, M. Marry, L. Krall, M. Kaye, B.E. Ramey, C. Fuqua, A.R. White, The effect of cellulose overproduction on binding and biofilm formation on roots by Agrobacterium tumefaciens, Molecular plant-microbe interactions 18 (9) (2005) 1002–1010. [60] S.J. Clough, K.-E. Lee, M.A. Schell, T.P. Denny, A two-component system in Ralstonia (Pseudomonas) solanacearum modulates production of PhcA-regulated virulence factors in response to 3-hydroxypalmitic acid methyl ester, J. Bacteriol. 179 (11) (1997) 3639–3648. [61] J.R. Joshi, S. Burdman, A. Lipsky, I. Yedidia, Effects of plant antimicrobial phenolic compounds on virulence of the genus Pectobacterium, Res. Microbiol. 166 (6) (2015) 535–545. [62] J.R. Joshi, N. Khazanov, H. Senderowitz, S. Burdman, A. Lipsky, I. Yedidia, Plant phenolic volatiles inhibit Quorum Sensing in pectobacteria and reduce their virulence by potential binding to ExpI and ExpR proteins, Sci. Rep. 6 (2016) 1–15. [63] F. Pantanella, P. Valenti, T. Natalizi, D. Passeri, F. Berlutti, Analytical techniques to study microbial biofilm on abiotic surfaces: pros and cons of the main techniques currently in use, Ann Ig 25 (1) (2013) 31–42. [64] F. Vazquez-Armenta, A. Bernal-Mercado, M. Tapia-Rodriguez, G. GonzalezAguilar, A. Lopez-Zavala, M. Martinez-Tellez, M. Hernandez-Oñate, J. AyalaZavala, Quercetin reduces adhesion and inhibits biofilm development by Listeria

[65]

[66]

[67]

[68]

[69] [70]

[71] [72] [73]

[74] [75]

[76] [77]

[78] [79]

[80] [81] [82]

[83]

[84]

[85] [86]

[87]

[88]

[89]

[90] [91]

[92]

[93]

290

monocytogenes by reducing the amount of extracellular proteins, Food Control 90 (2018) 266–273. D. Athinuwat, S. Brooks, T.J. Burr, S. Prathuangwong, Flagella and Pili of Xanthomonas axonopodis pv. glycines are associated with motility, biofilm formation and virulence on soybean, J. Phytopathol. 166 (7–8) (2018) 590–600. I. Pieretti, M. Royer, V. Barbe, S. Carrere, R. Koebnik, A. Couloux, A. Darrasse, J. Gouzy, M.-A. Jacques, E. Lauber, Genomic insights into strategies used by Xanthomonas albilineans with its reduced artillery to spread within sugarcane xylem vessels, BMC Genomics 13 (1) (2012) 1–23. J. Newton, R. Fray, Integration of environmental and host‐derived signals with Quorum Sensing during plant–microbe interactions, Cell Microbiol. 6 (3) (2004) 213–224. H. Liu, S.J. Coulthurst, L. Pritchard, P.E. Hedley, M. Ravensdale, S. Humphris, T. Burr, G. Takle, M.-B. Brurberg, P.R. Birch, Quorum Sensing coordinates brute force and stealth modes of infection in the plant pathogen Pectobacterium atrosepticum, PLoS Pathog. 4 (6) (2008) 1–11. F. Barras, F.d.r. van Gijsegem, A.K. Chatterjee, Extracellular enzymes and pathogenesis of soft-rot Erwinia, Annu. Rev. Phytopathol. 32 (1) (1994) 201–234. M. Potrykus, M. Golanowska, N. Hugouvieux-Cotte-Pattat, E. Lojkowska, Regulators involved in Dickeya solani virulence, genetic conservation, and functional variability, Mol. Plant Microbe Interact. 27 (7) (2014) 700–711. T.L. Johnson, J. Abendroth, W.G. Hol, M. Sandkvist, Type II secretion: from structure to function, FEMS Microbiol. Lett. 255 (2) (2006) 175–186. C. Baron, Antivirulence drugs to target bacterial secretion systems, Curr. Opin. Microbiol. 13 (1) (2010) 100–105. A. Gauthier, M.L. Robertson, M. Lowden, J.A. Ibarra, J.L. Puente, B.B. Finlay, Transcriptional inhibitor of virulence factors in enteropathogenic Escherichia coli, Antimicrob. Agents Chemother. 49 (10) (2005) 4101–4109. D.A. Rasko, V. Sperandio, Anti-virulence strategies to combat bacteria-mediated disease, Nat. Rev. Drug Discov. 9 (2) (2010) 117–128. D.L. Arnold, H.C. Lovell, R.W. Jackson, J.W. Mansfield, Pseudomonas syringae pv. phaseolicola: from ‘has bean’to supermodel, Mol. Plant Pathol. 12 (7) (2011) 617–627. D.C. Gross, Molecular and genetic analysis of toxin production by pathovars of Pseudomonas syringae, Annu. Rev. Phytopathol. 29 (1) (1991) 247–278. M. Kimura, H. Anzai, I. Yamaguchi, Microbial toxins in plant-pathogen interactions: biosynthesis, resistance mechanisms, and significance, J. Gen. Appl. Microbiol. 47 (4) (2001) 149–160. P.S. McManus, Does a drop in the bucket make a splash? Assessing the impact of antibiotic use on plants, Curr. Opin. Microbiol. 19 (2014) 76–82. Adama, Cuprimicín 100 Hyper, (2016) https://www.adama.com/mexico/es/ portafolio-de-soluciones/manejo-de-enfermedades/cuprimicin-100.html , Accessed date: 28 January 2019. SummitAgro, Agry-Gent Plus 800, (2013) file:///C:/Users/Usuario/Downloads/ Agrygent%20800.pdf , Accessed date: 13 November 2018. Suregold Bamargo, http://www.bamagro.com.mx/interior/contenido %20paginas/Suregold/index.html, (2015) , Accessed date: 13 November 2018. D.G. Deryabin, K.S. Inchagova, Inhibitory effect of aminoglycosides and tetracyclines on Quorum Sensing in Chromobacterium violaceum, Microbiology 87 (1) (2018) 1–8. X. Zeng, X. Liu, J. Bian, G. Pei, H. Dai, S.W. Polyak, F. Song, L. Ma, Y. Wang, L. Zhang, Synergistic effect of 14-alpha-lipoyl andrographolide and various antibiotics on the formation of biofilms and production of exopolysaccharide and pyocyanin by Pseudomonas aeruginosa, Antimicrob. Agents Chemother. 55 (6) (2011) 3015–3017. S. Vasudevan, S.S. Swamy, G. Kaur, S.A. Princy, P. Balamurugan, Synergism between Quorum Sensing inhibitors and antibiotics: combating the antibiotic resistance crisis, in: V.C. Kalia (Ed.), Biotechnological Applications of Quorum Sensing Inhibitors, Springer Singapore, Singapore, 2018, pp. 209–225. B.M. Ahmer, Cell‐to‐cell signalling in Escherichia coli and Salmonella enterica, Mol. Microbiol. 52 (4) (2004) 933–945. R. Van Houdt, A. Aertsen, P. Moons, K. Vanoirbeek, C.W. Michiels, N-acyl-Lhomoserine lactone signal interception by Escherichia coli, FEMS Microbiol. Lett. 256 (1) (2006) 83–89. H.-L. Wei, L.-Q. Zhang, Quorum-sensing system influences root colonization and biological control ability in Pseudomonas fluorescens 2P24, Antonie Leeuwenhoek 89 (2) (2006) 267–280. M.R. Tapia-Rodriguez, A. Hernandez-Mendoza, G.A. Gonzalez-Aguilar, M.A. Martinez-Tellez, C.M. Martins, J.F. Ayala-Zavala, Carvacrol as potential Quorum Sensing inhibitor of Pseudomonas aeruginosa and biofilm production on stainless steel surfaces, Food Control 75 (2017) 255–261. M. Rao, S. Padyana, K. Dipin, S. Kumar, B. Nayak, Antimicrobial compounds of plant origin as efflux pump inhibitors: new avenues for controlling multidrug resistant pathogens, Journal of Antimicrobial Agents 4 (1000159) (2018) 24721212.1000159. T.B. Rasmussen, M. Givskov, Quorum-sensing inhibitors as anti-pathogenic drugs, International Journal of Medical Microbiology 296 (2–3) (2006) 149–161. P. Vargas, G.A. Farias, J. Nogales, H. Prada, V. Carvajal, M. Barón, R. Rivilla, M. Martín, A. Olmedilla, M.T. Gallegos, Plant flavonoids target Pseudomonas syringae pv. tomato DC 3000 flagella and type III secretion system, Environmental microbiology reports 5 (6) (2013) 841–850. P. Truchado, A. Gil-Izquierdo, F. Tomas-Barberan, A. Allende, Inhibition by chestnut honey of N-Acyl-L-homoserine lactones and biofilm formation in Erwinia carotovora, Yersinia enterocolitica, and Aeromonas hydrophila, J. Agric. Food Chem. 57 (23) (2009) 11186–11193. M. Lemos, A. Borges, J. Teodósio, P. Araújo, F. Mergulhão, L. Melo, M. Simões,

Physiological and Molecular Plant Pathology 106 (2019) 281–291

M.M. Gutiérrez-Pacheco, et al.

[94]

[95]

[96]

[97]

The effects of ferulic and salicylic acids on Bacillus cereus and Pseudomonas fluorescens single-and dual-species biofilms, Int. Biodeterior. Biodegrad. 86 (2014) 42–51. L. Lagonenko, A. Lagonenko, A. Evtushenkov, Impact of salicylic acid on biofilm formation by plant pathogenic bacteria, Journal of Biology and Earth Sciences 3 (2) (2013) 176–181. L. Zhang, J. Xu, J. Xu, H. Zhang, L. He, J. Feng, TssB is essential for virulence and required for Type VI secretion system in Ralstonia solanacearum, Microb. Pathog. 74 (2014) 1–7. Y. Li, Q. Peng, D. Selimi, Q. Wang, A.O. Charkowski, X. Chen, C.-H. Yang, The plant phenolic compound p-coumaric acid represses gene expression in the Dickeya dadantii type III secretion system, Appl. Environ. Microbiol. 75 (5) (2009) 1223–1228. P. Truchado, F.A. Tomás-Barberán, M. Larrosa, A. Allende, Food phytochemicals act as Quorum Sensing inhibitors reducing production and/or degrading autoinducers of Yersinia enterocolitica and Erwinia carotovora, Food Control 24 (1) (2012) 78–85.

[98] J. Chen, Y. Yu, S. Li, W. Ding, Resveratrol and coumarin: novel agricultural antibacterial agent against Ralstonia solanacearum in vitro and in vivo, Molecules 21 (11) (2016) 1501. [99] Y. Zhang, J. Kong, Y. Xie, Y. Guo, Y. Cheng, H. Qian, W. Yao, Essential oil components inhibit biofilm formation in Erwinia carotovora and Pseudomonas fluorescens via anti-Quorum Sensing activity, LWT 92 (2018) 133–139. [100] C.-Y. Chang, T. Krishnan, H. Wang, Y. Chen, W.-F. Yin, Y.-M. Chong, L.Y. Tan, T.M. Chong, K.-G. Chan, Non-antibiotic Quorum Sensing inhibitors acting against N-acyl homoserine lactone synthase as druggable target, Sci. Rep. 4 (2014) 1–8. [101] T.A. Gould, H.P. Schweizer, M.E. Churchill, Structure of the Pseudomonas aeruginosa acyl‐homoserinelactone synthase LasI, Mol. Microbiol. 53 (4) (2004) 1135–1146. [102] J. Chung, E. Goo, S. Yu, O. Choi, J. Lee, J. Kim, H. Kim, J. Igarashi, H. Suga, J.S. Moon, Small-molecule inhibitor binding to an N-acyl-homoserine lactone synthase, Proc. Natl. Acad. Sci. Unit. States Am. 108 (29) (2011) 12089–12094. [103] N. Rai, R. Rai, K. Venkatesh, Quorum Sensing Biosensors, Quorum Sensing vs Quorum Quenching: A Battle with No End in Sight, Springer, 2015, pp. 173–183.

291