The importance of surface-active metabolites (biosurfactants) in cooperative 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 recognition that bacteria typically act as multicellular groups is providing key insights into the biology and ecology of microorganisms and should lead our research efforts to better understand the emergent properties of organized microbial communities. Indeed, the concept of bacteria as social organisms is profoundly altering our views of microbiology. «Swarming motility» is a poorly understood social behaviour of flagellated bacteria. The ubiquitous and 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, and intercellular communication in P. aeruginosa. Furthermore, we have extensively investigated the production of extracellular surface-active agents called rhamnolipids, a special bacterial feature required for the unique swarming phenotype. Known for more than 60 years and among the best studied biosurfactants, rhamnolipids comprise a diverse group of mono- and di-sugar amphiphilic glycolipids with surface-active properties. Produced by various bacteria, the best known being Pseudomonas aeruginosa and a few Burkholderia species, these molecules still hold many secrets and promises. Several other bacterial species also produce surface-active molecules. The exact reason why bacteria release surface-active molecules is still unclear, and many hypotheses have been proposed. Interestingly, we are currently finding surprising interactions between different bacterial species involving biosurfactants, for instance revealing that these surface-active molecules can act as shareable «public goods» providing emerging properties to mixed communities. Such approach is also suggesting that bacteria not previously known to swarm or produce surfactant can express new phenotypes when interacting with other microbial species. Because bacteria living on a surface share several features with swarming bacteria, we hypothesize that swarming motility reflects fundamental aspects of the cooperative social life of microbes. We will use swarming as a a model microbial cooperative behaviour. The principal working hypothesis that will drive this sociomicrobiology investigation is that biosurfactants are produced as mediators of microbial surface growth life. We will investigate how interactions with other bacterial species might modulate the production of these surface-active molecules. Bacteria typically live as multicellular organizations and communities. However, most of our knowledge on these organisms is mostly at the individual cell level, or as pure cultures. The research proposed here will enhance our understanding of the emergent properties of bacteria living as multicellular communities.