Limits...
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.

Show MeSH

Related in: MedlinePlus

Cell counts of GFP expressing PP9 cells in presence and absence of E. coli XL-1 Blue counterpart obtained from FACS.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2698150&req=5

pone-0006065-g007: Cell counts of GFP expressing PP9 cells in presence and absence of E. coli XL-1 Blue counterpart obtained from FACS.

Mentions: Based on the above results, it was further hypothesised that physical collision between cells might be playing a role by being recognized as presence of competing cells by PP9. As the cell number of the competing cells increased, physical collision would also increase, prompting PP9 to hasten BA utilization. To validate this, PP9 was inoculated with increasing cell density of E. coli JM 101 (PP9: E. coli JM101 in the log ratio 1∶0.5, 1∶1 and 1∶2) in Tris+BA medium. BA utilization was found to be the highest in the case of PP9: E. coli log ratio of 1∶2, followed by 1∶1 and the least in 1∶0.5 (Figure 4). The data clearly indicated that increasing cell density of the “competing” counterpart resulted in increasing BA utilisation by PP9. This could have been achieved by means of an increase in the expression of proteins responsible for BA utilisation. We observed an increase in GFP expression (putatively, a consequence of enhanced TOL expression) in response to increased “competitor” density in the shake flasks (Figure 5). To further establish that the presence of another strain in the mixed culture leads to enhanced expression of TOL in PP9, we performed flow cytometry experiments. For FACS analysis, instead of E. coli JM 101 (used in the previous experiments) we have used DsRed-bearing E. coli Strain XL-1 Blue (see Table 1) to differentiate and count the populations of PP9 and E. coli. Cultures of PP9, PP9: E. coli XL-1 Blue (log ratio 1∶1) and PP9: E. coli XL-1 Blue (log ratio 1∶2) were grown in presence of 5 mM BA and analysed after 0 h and 24 h (Figure 6 and 7). At the end of 24 h, the GFP positive cells in PP9 alone culture had increased by 3 fold, whereas in the PP9: E.coli XL-1 Blue (log ratio 1∶1) and PP9: E. coli XL-1 Blue (log ratio 1∶2) cultures, the increase was 34 and 87 fold, respectively (Figure 7). The FACS results lend credible support to our contention that enhanced BA degradation is mediated via TOL plasmid activation, which in turn, is related to the cell density of the “competing” species. Seen together with data presented in Figure 2, the FACS results unequivocally show the tremendous competitive edge derived by PP9 by employing this kind of strategy.


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

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

Cell counts of GFP expressing PP9 cells in presence and absence of E. coli XL-1 Blue counterpart obtained from FACS.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0006065-g007: Cell counts of GFP expressing PP9 cells in presence and absence of E. coli XL-1 Blue counterpart obtained from FACS.
Mentions: Based on the above results, it was further hypothesised that physical collision between cells might be playing a role by being recognized as presence of competing cells by PP9. As the cell number of the competing cells increased, physical collision would also increase, prompting PP9 to hasten BA utilization. To validate this, PP9 was inoculated with increasing cell density of E. coli JM 101 (PP9: E. coli JM101 in the log ratio 1∶0.5, 1∶1 and 1∶2) in Tris+BA medium. BA utilization was found to be the highest in the case of PP9: E. coli log ratio of 1∶2, followed by 1∶1 and the least in 1∶0.5 (Figure 4). The data clearly indicated that increasing cell density of the “competing” counterpart resulted in increasing BA utilisation by PP9. This could have been achieved by means of an increase in the expression of proteins responsible for BA utilisation. We observed an increase in GFP expression (putatively, a consequence of enhanced TOL expression) in response to increased “competitor” density in the shake flasks (Figure 5). To further establish that the presence of another strain in the mixed culture leads to enhanced expression of TOL in PP9, we performed flow cytometry experiments. For FACS analysis, instead of E. coli JM 101 (used in the previous experiments) we have used DsRed-bearing E. coli Strain XL-1 Blue (see Table 1) to differentiate and count the populations of PP9 and E. coli. Cultures of PP9, PP9: E. coli XL-1 Blue (log ratio 1∶1) and PP9: E. coli XL-1 Blue (log ratio 1∶2) were grown in presence of 5 mM BA and analysed after 0 h and 24 h (Figure 6 and 7). At the end of 24 h, the GFP positive cells in PP9 alone culture had increased by 3 fold, whereas in the PP9: E.coli XL-1 Blue (log ratio 1∶1) and PP9: E. coli XL-1 Blue (log ratio 1∶2) cultures, the increase was 34 and 87 fold, respectively (Figure 7). The FACS results lend credible support to our contention that enhanced BA degradation is mediated via TOL plasmid activation, which in turn, is related to the cell density of the “competing” species. Seen together with data presented in Figure 2, the FACS results unequivocally show the tremendous competitive edge derived by PP9 by employing this kind of strategy.

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
Related in: MedlinePlus