Osmotic spreading of Bacillus subtilis biofilms driven by an extracellular matrix
Bacteria thrive in colonies which form stable biological havens called biofilms on nutrient-rich substrates. Biofilms are highly organized bio-masses composed of differentiated bacterial cells and their cellular secretions that form a matrix around the cells. The composition and functionalities of these extracellular matrices are very intriguing; to name a few, they provide protective environs for bacteria and also serve as nutrient reservoirs. Biofilms are hardly static but given enough nutrients in the host medium, they grow and spread. The spread of biofilms may be linked to active motility and multiplication of bacterial cells themselves or changes in the surrounding extracellular matrix or both. In the paper, the authors for the first time provide evidence that biofilm spreading is largely driven by osmotic forces in the extracellular matrix rather than by cellular motility.