Biofilms: The Secret Story Of Microbial Communities

This chapter is dedicated to a particular phase of the bacterial cell cycle known as the biofilm, in which single-celled individuals gather together to form a sedentary but dynamic community with a complex structure, displaying spatial and functional heterogeneity. In response to the perception of environmental signals by sensing systems, appropriate responses are triggered, leading to biofilm formation. This process involves various molecular systems (described in detail here for Gram-negative and Gram-positive bacteria) enabling bacteria to identify appropriate surfaces on which to anchor themselves, to stick to those surfaces and to each other, to construct multicellular communities several hundreds of micrometers thick and to detach from the community. These molecular systems are used antagonistically or synergistically, depending on the microenvironment confronting the bacterium. The biofilm microbial community is a unique, highly competitive and crowded environment facilitating microevolutionary processes and horizontal gene transfer between distantly related microorganisms. It is governed by social rules, based on the production and use of 'public' goods, with actors and recipients. Biofilms constitute a unique shield against external aggressions, including drug treatment and immune reactions. Biofilm-associated infections in humans have therefore generated major problems for the diagnosis and treatment of disease. Improvements in our understanding of biofilms have led to innovative research aiming to interfere with the process of biofilm formation.