Abstract

Biofilms, which are bacterial communities colonizing interfaces, often display incredible phenotypic heterogeneity, even in monoclonal populations. Two among the many possible behaviours observed across cells are motility and matrix production. In B. subtilis, the two gene expression pathways that lead to these phenotypes are mutually exclusive, so that a cell can either be in one state or the other. While the role of matrix production during biofilm development is very well studied and known to be necessary for the emergence of “wrinkles” in many biofilms grown on hard substrate, the role of motility in these conditions is much less clear.

While analyzing the spatio-temporal gene expression pattern during biofilm development, we found the presence of “motility pulses” that reproducibly occur along the biofilm wrinkles, raising the question of whether the liquid channels underneath the wrinkles could be used by cells within the centre of the biofilm to escape to the outside. By developing a simple yet effective setup that allows us to change the environment experienced by the biofilms without disturbing the biofilm structure, we confirmed not only that escape is possible, but that cell motility is a necessary condition. Importantly, we show that this mechanism, which requires coordination between motility and matrix production, can be used by resistant cells to escape the core of a biofilm and rescue the population upon antibiotic treatment.