Swarming motility as a model microbial cooperative behaviour and importance of surfactants as socially beneficial exoproducts of bacteria

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 should lead research efforts to better understand the emergent properties of organized microbial communities. «Swarming motility» is a poorly understood social behaviour of flagellated bacteria. A key requirement for swarming is surface conditioning achieved by the production of a surface-active/wetting agent (surfactant) that reduced the surface tension surrounding the cells. The ubiquitous and versatile opportunistic pathogen Pseudomonas aeruginosa is one of the most widely studied bacterial species in sociomicrobiology research. We have been investigating the mechanisms involved in swarming motility in this bacterium, especially the production of rhamnolipids, its surface-active agent. Recent advancements in our understanding of surfactant production and functions will be presented, emphasizing their role as as mediators of microbial surface growth life, not only in Pseudomonas but also in other bacteria such as species of Burkholderia. An example of interactions between different bacterial species involving surfactants will be discussed, revealing that these surface-active molecules can act as shareable «public goods», socially beneficial metabolites providing emerging properties to mixed communities.