In nature, Bacillus subtilis resides in multicellular communities, also called biofilms. In a biofilm cells are embedded in an extracellular matrix, a network of biopolymers composed of polysaccharides and proteins. In Gram-positive bacteria, the cell wall is the anchor point for the extracellular matrix.
We performed a systematic analysis of cell wall components that specifically disturb biofilm formation. Biofilm development was dramatically disturbed by non-canonical D-amino acids, depletion of cell-wall polysaccharides and specific interference with peptidoglycan assembly. Strikingly, none of these cell wall disturbances affected planktonic growth or interfered with the expression of major biofilm regulators. A careful analysis of the biofilm morphology revealed that these cell wall modifications altered the composition and anchoring of the extracellular matrix. We also observed changes in the global protein profile upon modification of the cell wall. Proteins involved in assembly of lipid rafts were highly induced and a dramatic increase in the levels of KatA (a catalase) and proteins involved in iron-sulfur cluster formation was observed. Thus, specific biofilm inhibitors that target the cell wall also induce a dramatic ROS (reactive oxygen species) response within the cells.
In conclusion, our work demonstrates that biofilm forming cells are more sensitive to cell wall modifications. We are now interested to fully comprehend the molecular mechanisms by which biofilm forming cells mediate their response to cell wall interferences. Especially, we are intrigued to map the novel links between cell wall stress within developing biofilms and the ROS response.
