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Competition triggers plasmid-mediated enhancement of substrate utilisation in Pseudomonas putida.

Joshi H, Dave R, Venugopalan VP - PLoS ONE (2009)

Bottom Line: Inert microspheres mimicking competitor cell size and concentration did not elicit any significant induction, further suggesting the role of physical cell-cell interaction.We conclude that P. putida harbouring pWW0 experience a competitive stress when grown as dual-species consortium, irrespective of the counterpart being BA degrader or not.The immediate effect of this stress is a marked increase in expression of TOL, leading to rapid utilization of the available carbon source and massive increase in its population density.

View Article: PubMed Central - PubMed

Affiliation: Biofouling and Biofilm Processes Section, Water and Steam Chemistry Division, BARC Facilities, Kalpakkam, India.

ABSTRACT
Competition between species plays a central role in the activity and structure of communities. Stable co-existence of diverse organisms in communities is thought to be fostered by individual tradeoffs and optimization of competitive strategies along resource gradients. Outside the laboratory, microbes exist as multispecies consortia, continuously interacting with one another and the environment. Survival and proliferation of a particular species is governed by its competitive fitness. Therefore, bacteria must be able to continuously sense their immediate environs for presence of competitors and prevailing conditions. Here we present results of our investigations on a novel competition sensing mechanism in the rhizosphere-inhabiting Pseudomonas putida KT2440, harbouring gfpmut3b-modified Kan(R) TOL plasmid. We monitored benzyl alcohol (BA) degradation rate, along with GFP expression profiling in mono species and dual species cultures. Interestingly, enhanced plasmid expression (monitored using GFP expression) and consequent BA degradation were observed in dual species consortia, irrespective of whether the competitor was a BA degrader (Pseudomonas aeruginosa) or a non-degrader (E. coli). Attempts at elucidation of the mechanistic aspects of induction indicated the role of physical interaction, but not of any diffusible compounds emanating from the competitors. This contention is supported by the observation that greater induction took place in presence of increasing number of competitors. Inert microspheres mimicking competitor cell size and concentration did not elicit any significant induction, further suggesting the role of physical cell-cell interaction. Furthermore, it was also established that cell wall compromised competitor had minimal induction capability. We conclude that P. putida harbouring pWW0 experience a competitive stress when grown as dual-species consortium, irrespective of the counterpart being BA degrader or not. The immediate effect of this stress is a marked increase in expression of TOL, leading to rapid utilization of the available carbon source and massive increase in its population density. The plausible mechanisms behind the phenomenon are hypothesised and practical implications are indicated and discussed.

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Time course of BA degradation in co-cultures of PP9+E. coli JM 101, PAO1+E. coli JM 101 and PP9+PAO1.106 cells each of PP9+E. coli JM 10, PAO1+E.coli JM 101and PP9+PAO1were inoculated in Tris+BA medium and incubated at 100 rpm and 30°C. Samples were withdrawn at regular time intervals and the residual BA was estimated by HPLC.
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pone-0006065-g003: Time course of BA degradation in co-cultures of PP9+E. coli JM 101, PAO1+E. coli JM 101 and PP9+PAO1.106 cells each of PP9+E. coli JM 10, PAO1+E.coli JM 101and PP9+PAO1were inoculated in Tris+BA medium and incubated at 100 rpm and 30°C. Samples were withdrawn at regular time intervals and the residual BA was estimated by HPLC.

Mentions: The above results indicate that PP9 was able to utilise BA much more efficiently when it was grown as a co-culture rather than as a monoculture. To further confirm whether the faster resource BA utilization by PP9 is triggered by the presence of another organism and whether PP9 resorts to enhanced BA degradation only when the counterpart has the ability to utilize the same carbon source, we utilized the BA non-degrader E. coli JM101 in place of PAO1 in the dual species experiments. Cells of E. coli JM 101 and PAO1 (106 each) and PP9 and E. coli JM 101 (106 each) were inoculated in shaking flask containing Tris minimal media with 5 mM BA. The BA utilization rate of PP9: E. coli JM101 (degrader and non-degrader) was similar to the BA utilization rate of PP9: PAO1 (both degraders) (Figure 3). The former dual culture utilized BA completely in 27 h whereas the latter did it in 24 h. Interestingly, the results indicated that, when E. coli JM101 (non-degrader) was inoculated along with PAO1 (degrader sans the plasmid), there was no increase in the BA utilization compared to when E. coli JM 101 was used together with PP9 (Figure 3), indicating that enhanced degradation takes place only in the case of the plasmid-bearer. Moreover, after 30 h the PAO1: E. coli JM101system had only utilized just 4% of the initial BA.


Competition triggers plasmid-mediated enhancement of substrate utilisation in Pseudomonas putida.

Joshi H, Dave R, Venugopalan VP - PLoS ONE (2009)

Time course of BA degradation in co-cultures of PP9+E. coli JM 101, PAO1+E. coli JM 101 and PP9+PAO1.106 cells each of PP9+E. coli JM 10, PAO1+E.coli JM 101and PP9+PAO1were inoculated in Tris+BA medium and incubated at 100 rpm and 30°C. Samples were withdrawn at regular time intervals and the residual BA was estimated by HPLC.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2698150&req=5

pone-0006065-g003: Time course of BA degradation in co-cultures of PP9+E. coli JM 101, PAO1+E. coli JM 101 and PP9+PAO1.106 cells each of PP9+E. coli JM 10, PAO1+E.coli JM 101and PP9+PAO1were inoculated in Tris+BA medium and incubated at 100 rpm and 30°C. Samples were withdrawn at regular time intervals and the residual BA was estimated by HPLC.
Mentions: The above results indicate that PP9 was able to utilise BA much more efficiently when it was grown as a co-culture rather than as a monoculture. To further confirm whether the faster resource BA utilization by PP9 is triggered by the presence of another organism and whether PP9 resorts to enhanced BA degradation only when the counterpart has the ability to utilize the same carbon source, we utilized the BA non-degrader E. coli JM101 in place of PAO1 in the dual species experiments. Cells of E. coli JM 101 and PAO1 (106 each) and PP9 and E. coli JM 101 (106 each) were inoculated in shaking flask containing Tris minimal media with 5 mM BA. The BA utilization rate of PP9: E. coli JM101 (degrader and non-degrader) was similar to the BA utilization rate of PP9: PAO1 (both degraders) (Figure 3). The former dual culture utilized BA completely in 27 h whereas the latter did it in 24 h. Interestingly, the results indicated that, when E. coli JM101 (non-degrader) was inoculated along with PAO1 (degrader sans the plasmid), there was no increase in the BA utilization compared to when E. coli JM 101 was used together with PP9 (Figure 3), indicating that enhanced degradation takes place only in the case of the plasmid-bearer. Moreover, after 30 h the PAO1: E. coli JM101system had only utilized just 4% of the initial BA.

Bottom Line: Inert microspheres mimicking competitor cell size and concentration did not elicit any significant induction, further suggesting the role of physical cell-cell interaction.We conclude that P. putida harbouring pWW0 experience a competitive stress when grown as dual-species consortium, irrespective of the counterpart being BA degrader or not.The immediate effect of this stress is a marked increase in expression of TOL, leading to rapid utilization of the available carbon source and massive increase in its population density.

View Article: PubMed Central - PubMed

Affiliation: Biofouling and Biofilm Processes Section, Water and Steam Chemistry Division, BARC Facilities, Kalpakkam, India.

ABSTRACT
Competition between species plays a central role in the activity and structure of communities. Stable co-existence of diverse organisms in communities is thought to be fostered by individual tradeoffs and optimization of competitive strategies along resource gradients. Outside the laboratory, microbes exist as multispecies consortia, continuously interacting with one another and the environment. Survival and proliferation of a particular species is governed by its competitive fitness. Therefore, bacteria must be able to continuously sense their immediate environs for presence of competitors and prevailing conditions. Here we present results of our investigations on a novel competition sensing mechanism in the rhizosphere-inhabiting Pseudomonas putida KT2440, harbouring gfpmut3b-modified Kan(R) TOL plasmid. We monitored benzyl alcohol (BA) degradation rate, along with GFP expression profiling in mono species and dual species cultures. Interestingly, enhanced plasmid expression (monitored using GFP expression) and consequent BA degradation were observed in dual species consortia, irrespective of whether the competitor was a BA degrader (Pseudomonas aeruginosa) or a non-degrader (E. coli). Attempts at elucidation of the mechanistic aspects of induction indicated the role of physical interaction, but not of any diffusible compounds emanating from the competitors. This contention is supported by the observation that greater induction took place in presence of increasing number of competitors. Inert microspheres mimicking competitor cell size and concentration did not elicit any significant induction, further suggesting the role of physical cell-cell interaction. Furthermore, it was also established that cell wall compromised competitor had minimal induction capability. We conclude that P. putida harbouring pWW0 experience a competitive stress when grown as dual-species consortium, irrespective of the counterpart being BA degrader or not. The immediate effect of this stress is a marked increase in expression of TOL, leading to rapid utilization of the available carbon source and massive increase in its population density. The plausible mechanisms behind the phenomenon are hypothesised and practical implications are indicated and discussed.

Show MeSH