Microbial quorum sensing signals, symbiosis, secrets and sabotage.

Bacteria exhibit sophisticated forms of multicellularity by coordinating the activities of individual cells with respect to behaviours such as symbiosis, conjugation, competence, swarming, secondary metabolite production, biofilm formation, growth inhibition, niche adaptation and virulence. Apart from direct cell-cell contact, the synthesis, release and perception of small diffusible chemicals acting as inter-cellular signals offer the most obvious mechanism for bacterial cell populations to synchronize their behaviour. Such cell-cell communication (quorum sensing) offers a unique framework for understanding how bacteria convert chemical information into coordinated group behaviours. It is deeply influenced by ecology, host interactions, chemical diversity and spatial architecture. Despite much progress, many fundamental questions remain unresolved, especially in natural, polymicrobial and host-associated environments. Here, we summarize our current understanding of bacterial cell-cell communication and main knowledge gaps and highlight examples of translational opportunities.