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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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Plate count of PP9, PAO1 and PP9+PAO1 grown as mono and dual cultures.PP9 (106 cells), PAO1 (106 cells) and PP9+PA01 (106 cells each) were inoculated in Tris+BA medium and incubated at 100 rpm and 30°C. Samples were withdrawn at regular time intervals and the samples were plated in respective antibiotic containing media for enumeration.
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pone-0006065-g002: Plate count of PP9, PAO1 and PP9+PAO1 grown as mono and dual cultures.PP9 (106 cells), PAO1 (106 cells) and PP9+PA01 (106 cells each) were inoculated in Tris+BA medium and incubated at 100 rpm and 30°C. Samples were withdrawn at regular time intervals and the samples were plated in respective antibiotic containing media for enumeration.

Mentions: It is possible that enhanced degradation was a result of combined action by the two degraders. However, if one of the two were to degrade the sole carbon source more competitively than the other, one would expect its number to go up in the culture. To investigate whether or not a particular organism flourished better when co-cultivated, we performed bacterial counts of the individual organisms at various time intervals. We plated samples of the mixed species consortium on luria agar containing gentamicin 25 µg.ml−1 (to count PAO1) and luria agar containing kanamycin 30 µg.ml−1 (to count PP9). As can be seen from the results, PP9 outnumbered PAO1, indicating that the former numerically outcompeted the latter (though both are BA-degraders) when the two were grown together (Figure 2).


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

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

Plate count of PP9, PAO1 and PP9+PAO1 grown as mono and dual cultures.PP9 (106 cells), PAO1 (106 cells) and PP9+PA01 (106 cells each) were inoculated in Tris+BA medium and incubated at 100 rpm and 30°C. Samples were withdrawn at regular time intervals and the samples were plated in respective antibiotic containing media for enumeration.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0006065-g002: Plate count of PP9, PAO1 and PP9+PAO1 grown as mono and dual cultures.PP9 (106 cells), PAO1 (106 cells) and PP9+PA01 (106 cells each) were inoculated in Tris+BA medium and incubated at 100 rpm and 30°C. Samples were withdrawn at regular time intervals and the samples were plated in respective antibiotic containing media for enumeration.
Mentions: It is possible that enhanced degradation was a result of combined action by the two degraders. However, if one of the two were to degrade the sole carbon source more competitively than the other, one would expect its number to go up in the culture. To investigate whether or not a particular organism flourished better when co-cultivated, we performed bacterial counts of the individual organisms at various time intervals. We plated samples of the mixed species consortium on luria agar containing gentamicin 25 µg.ml−1 (to count PAO1) and luria agar containing kanamycin 30 µg.ml−1 (to count PP9). As can be seen from the results, PP9 outnumbered PAO1, indicating that the former numerically outcompeted the latter (though both are BA-degraders) when the two were grown together (Figure 2).

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