Biofilm formation displays intrinsic offensive and defensive features of Bacillus cereus

Biofilm formation is a strategy of many bacterial species to adapt to a variety of stresses and has become a part of infections, contaminations or beneficial interactions. In this study, we demonstrate that profound physiological changes permit Bacillus cereus to switch from a floating to a sessile lifestyle, to undergo further maturation of the biofilm, and to differentiate into offensive or defensive populations. The rearrangement of nucleotides, sugars, amino acids and energy metabolism lead to changes promoting reinforcement of the cell wall, rigidity of the membrane, activation of ROS detoxification or secondary metabolite production, all contributing to defend biofilm cells from external aggressions. However, floating cells maintain a fermentative metabolic status that ensures a higher aggressiveness against hosts, evidenced by the production of toxins and other virulent factors. Our findings argue in favor of the metabolic versatility of B. cereus and the fine tuning of these gene expression which grant this species to move to any of these two distinct subpopulations, necessary to face changeable environmental conditions.