The importance of surface-active metabolites (biosurfactants) in bacterial social behaviours

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In their natural ecosystems, bacteria persist as microbial communities, where they exploit elaborate systems of intercellular interaction and communication to adapt to changing environmental conditions. The concept of bacteria as social organisms is profoundly altering our views of microbiology. Biofilms, the preferred modes of growth of bacteria in the natural environment and the best-studied examples of microbial communities, help bacteria to survive under unfavourable conditions. The importance of biofilms in the biotechnological and medical fields is increasingly evident. «Swarming motility», a poorly understood social behaviour of flagellated bacteria is believed to be relevant to the identification of genes and mechanisms involved in multicellular activities. The ubiquitous and extremely versatile Pseudomonas aeruginosa is the most widely studied bacterial species in sociomicrobiology research. We have previously revealed a number of mechanisms involved in swarming motility, biofilm formation and intercellular communication in P. aeruginosa. Furthermore, we have extensively investigated the production of extracellular wetting and chemotactic agents called rhamnolipids, a special bacterial feature required for the unique swarming phenotype. We have recently identified an hybrid sensory system that is key to normal swarming motility, and that is independent of rhamnolipid production. Significantly, this sensory system appears involved in mediating the expression of swarming motility and biofilm development specifically by detection of surfaces. Because bacteria living on a surface share several features with swarming bacteria, we hypothesize that swarming motility reflects fundamental aspects of biofilm development. Two principal working hypotheses will drive this sociomicrobiology investigation: (1) rhamnolipids function as a mechanism promoting bacteria dispersal/ecosystem colonization. Our preliminary results suggest that production of rhamnolipids is promoted by restricting growth conditions, thus supporting the benefit of dispersion/enhanced colonization of new niches, (2) Specific sensory pathways specially responding to growth on a surface modulate the regulatory mechanisms required for swarming motility. This proposed research project aims at further improve our understanding of the multicellular functions of bacteria through the study of swarming motility as a model microbial social behaviour. We are using a multi-faceted approach, primarily based on a combination of microbial physiology functional genomics, and chemical biology, to gain insight into swarming motility and determine its significance. Knowledge gain also contributes to reveal avenues to control the establishment of bacterial biofilms.