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Bacteriostasis and the inoculation of phosphate-solubilizing bacteria in the rhizosphere
SHORT Bacteriostasis and the insulation
J. A. Estaciitn
Experimentai
OCAMPO,
COMMUNICATION of phosphate-solubili~ing bacteria in the rhizosphere
J. M.
BAREA
and E.
de1 Zaidin.
Avda. Cervantes.
(Acrepred
6 M~rrch 1978)
MOKTOYA
No. I, Granada.
Spain
Bacteriostasis has been described as a factor that can inat the beginning of the assay, sensitivity of phosphobachibit or reduce the development of bacteria in soil (Brown, teria to bacteriostasis increased with time and reached a 1973). Davis (1975 and 1976) found that many bacteria maximum at the middle of the experiment. There was no were sensitive to bacteriostasis. Bacteriostasis is only opersigni~cant change in the bacteriostatic acti\tity, when NPK ative at low nutrient levels, and is overcome by the addifertilizers were applied (treatment 2). tion of mineral salts to the soil. The cause of soil bacterioBacteriostasis was always overcome in pots where an stasis is as yet unexplained. although it seems that it is NPK fertilizer was added to the plants at the middie of of biological origin. the assay (treatments 3 and 4) and by the age of plant. In an experimental inoculation of A:otohacfer into the Thus, agreeing with Brown (1973). that a certain role can rhizosphere of lavender, Barea et al. (1978) found that A;Obe attributed to the plant winch behaved as if supplying rohocter was sensitive to such factors. and the activity of substances to overcome bacteriostasis. this seemed to coincide with the decrease in .Axrabucrzr Figure 2 shows the course of development of phosphonumbers in the rhizosphere. bacteria inoculated in the lavender rhizosphere. UndoubtWe have examined the effects of soil bacteriostasis on edly, soil bacteriostasis might have some influence on the the establishment of phosphate-solubilizing bacteria (phosestablishment of phosphobacteria, but as Fig. I (treatment phobacteria) inoculated into the rhizosphere of lavender 2) clearly shows, its effect on phosphobacteria remained (tcit~&uiu spiccr var. CZI’UL). almost constant until the middle of the assay, whereas the Microorganisms, plants and treatments used in the glassnumber of inoculated phosphobacteria (Fig. 2) declined at house experiment were described by Ocampo (‘I ai. (19753. Unsterilized field soil No. 1 amended with 3”,, farmyard manure was used. Three phosphate-soiubilizin~ bacteria. a ~,s~,~~~o~~~[~~~u.~ sp., a Btrciilus sp. and an ~~~~~bu~~~$iu/?~ sp. were each cultured in Brown’s medium (1972). AI the time of inoculation the three cultures were mixed. Each seedling received about IO” phosphobacteria cells. There were four NPK treatments: I = no NPK added; T 2 = NPK added at the time of bacterial inoculation; 3 = NPK added at 10 weeks and 4 = treatments 2 + 3. This fertilizer was prepared in the following way: 8.8g KHIPO, and 75.7g N&NO, were dissolved m 11 distilled water and 10 ml of this fertilizer were added per kg solI in which lavender was grown at the time stated. Rhirosphere soil from replicate plants was sampled every 15 days. Two separate measurements of prowth of p)losphobacteria were made using these samples: (1) the course of development of the bacterial inoculum added to the pots. Bacteria able to solubllize rock phosphate were counted (Ocampo of uf., 1975) and (2) the bacteriostatic acti~rty. To assess soil bacteriostasis to phosphobacteria, a technique based on that described by Brown (1973) was used. Rhizosphere soil from each sample was placed in Petri dishes and moistened. Disks of sterile filter paper were either placed on the soil, or in sterile dishes as controls. Agar-disks 7 mm dia (9 replicates!samplc), cut from I I I I 1 I 1 I l.S”,, sterile water-agar, were placed on the filter paper. 0 16 0 4 IO Dishes were kept at 26 C for 15 h and separate agar-disks were then inoculated with 10 ml of a suspension of a phosWeeks after Inoculation phohacterium (3wiffu.ssp.,Ps~cnf~f~~ilo~,its sp and -t
Short communications this time. Thus. a much more possible explanation for the decrease of phosphobacteria could be the effect of microorganisms acting by producing antibiotics or lytic enzymes (unpublished data). REFERENCES
0
IO
4
Weeks
after
16
inoculation
Fig. 2. Numbers of inoculated phosphobacteria zosphere of lavender receiving different NPK (See Fig. I).
m the rhitreatments.
BROWN M. E. (1972) Plant growth substances produced by microorganisms of soil and rhizosphere. J. rlppl. Bwt. 35, 443-451. BROWN M. E. (1973) Soil bacteriostasis limitation in growth of soil and rhizosphere bacteria. C‘un. J. M~robid. 19, lY5-~199. BAREA J. M., OCAMPO J. A., ALC.OX R.. OI.I~AK~.S J. and MONTOYA E. (lY78) Effects of ecological factors on the establishment of A~orohacrrr in the rhizosphere. Environmental Role of Nitrogen-fixing Blue-green Algae and Asymbiotic Bacteria. Bull. WO/. Rcs. Co~tmw~. (S~ockh.) 26, 3% 330. DAVIS R. D. (1975) Soil bacteriostasis: inhIbItion of spore germination and microcolony development in agar disks incubated on nonsterile soils. C’ctn. J. Microhiol. 21, l27&l272. DAVIS R. D. (1976) Soil bacteriostasis: relation to bacterial nutrition and active soil inhibition. Soil Biol. Rioc~henl. 8, 429- 433. OCAMPCI J. A., BAREA J. M. and MONTCIYA E (1975) Interactions between Azorohactrt and phosphobacteria and their establishment in the rhirosphere as affected by soil fertility. Ctrn. J. Mic~rohiol. 21, 116&l 165.
J. A. Estaciitn
Experimentai
OCAMPO,
COMMUNICATION of phosphate-solubili~ing bacteria in the rhizosphere
J. M.
BAREA
and E.
de1 Zaidin.
Avda. Cervantes.
(Acrepred
6 M~rrch 1978)
MOKTOYA
No. I, Granada.
Spain
Bacteriostasis has been described as a factor that can inat the beginning of the assay, sensitivity of phosphobachibit or reduce the development of bacteria in soil (Brown, teria to bacteriostasis increased with time and reached a 1973). Davis (1975 and 1976) found that many bacteria maximum at the middle of the experiment. There was no were sensitive to bacteriostasis. Bacteriostasis is only opersigni~cant change in the bacteriostatic acti\tity, when NPK ative at low nutrient levels, and is overcome by the addifertilizers were applied (treatment 2). tion of mineral salts to the soil. The cause of soil bacterioBacteriostasis was always overcome in pots where an stasis is as yet unexplained. although it seems that it is NPK fertilizer was added to the plants at the middie of of biological origin. the assay (treatments 3 and 4) and by the age of plant. In an experimental inoculation of A:otohacfer into the Thus, agreeing with Brown (1973). that a certain role can rhizosphere of lavender, Barea et al. (1978) found that A;Obe attributed to the plant winch behaved as if supplying rohocter was sensitive to such factors. and the activity of substances to overcome bacteriostasis. this seemed to coincide with the decrease in .Axrabucrzr Figure 2 shows the course of development of phosphonumbers in the rhizosphere. bacteria inoculated in the lavender rhizosphere. UndoubtWe have examined the effects of soil bacteriostasis on edly, soil bacteriostasis might have some influence on the the establishment of phosphate-solubilizing bacteria (phosestablishment of phosphobacteria, but as Fig. I (treatment phobacteria) inoculated into the rhizosphere of lavender 2) clearly shows, its effect on phosphobacteria remained (tcit~&uiu spiccr var. CZI’UL). almost constant until the middle of the assay, whereas the Microorganisms, plants and treatments used in the glassnumber of inoculated phosphobacteria (Fig. 2) declined at house experiment were described by Ocampo (‘I ai. (19753. Unsterilized field soil No. 1 amended with 3”,, farmyard manure was used. Three phosphate-soiubilizin~ bacteria. a ~,s~,~~~o~~~[~~~u.~ sp., a Btrciilus sp. and an ~~~~~bu~~~$iu/?~ sp. were each cultured in Brown’s medium (1972). AI the time of inoculation the three cultures were mixed. Each seedling received about IO” phosphobacteria cells. There were four NPK treatments: I = no NPK added; T 2 = NPK added at the time of bacterial inoculation; 3 = NPK added at 10 weeks and 4 = treatments 2 + 3. This fertilizer was prepared in the following way: 8.8g KHIPO, and 75.7g N&NO, were dissolved m 11 distilled water and 10 ml of this fertilizer were added per kg solI in which lavender was grown at the time stated. Rhirosphere soil from replicate plants was sampled every 15 days. Two separate measurements of prowth of p)losphobacteria were made using these samples: (1) the course of development of the bacterial inoculum added to the pots. Bacteria able to solubllize rock phosphate were counted (Ocampo of uf., 1975) and (2) the bacteriostatic acti~rty. To assess soil bacteriostasis to phosphobacteria, a technique based on that described by Brown (1973) was used. Rhizosphere soil from each sample was placed in Petri dishes and moistened. Disks of sterile filter paper were either placed on the soil, or in sterile dishes as controls. Agar-disks 7 mm dia (9 replicates!samplc), cut from I I I I 1 I 1 I l.S”,, sterile water-agar, were placed on the filter paper. 0 16 0 4 IO Dishes were kept at 26 C for 15 h and separate agar-disks were then inoculated with 10 ml of a suspension of a phosWeeks after Inoculation phohacterium (3wiffu.ssp.,Ps~cnf~f~~ilo~,its sp and -t
Short communications this time. Thus. a much more possible explanation for the decrease of phosphobacteria could be the effect of microorganisms acting by producing antibiotics or lytic enzymes (unpublished data). REFERENCES
0
IO
4
Weeks
after
16
inoculation
Fig. 2. Numbers of inoculated phosphobacteria zosphere of lavender receiving different NPK (See Fig. I).
m the rhitreatments.
BROWN M. E. (1972) Plant growth substances produced by microorganisms of soil and rhizosphere. J. rlppl. Bwt. 35, 443-451. BROWN M. E. (1973) Soil bacteriostasis limitation in growth of soil and rhizosphere bacteria. C‘un. J. M~robid. 19, lY5-~199. BAREA J. M., OCAMPO J. A., ALC.OX R.. OI.I~AK~.S J. and MONTOYA E. (lY78) Effects of ecological factors on the establishment of A~orohacrrr in the rhizosphere. Environmental Role of Nitrogen-fixing Blue-green Algae and Asymbiotic Bacteria. Bull. WO/. Rcs. Co~tmw~. (S~ockh.) 26, 3% 330. DAVIS R. D. (1975) Soil bacteriostasis: inhIbItion of spore germination and microcolony development in agar disks incubated on nonsterile soils. C’ctn. J. Microhiol. 21, l27&l272. DAVIS R. D. (1976) Soil bacteriostasis: relation to bacterial nutrition and active soil inhibition. Soil Biol. Rioc~henl. 8, 429- 433. OCAMPCI J. A., BAREA J. M. and MONTCIYA E (1975) Interactions between Azorohactrt and phosphobacteria and their establishment in the rhirosphere as affected by soil fertility. Ctrn. J. Mic~rohiol. 21, 116&l 165.