Microbial communities governed by interplay of bacterial interaction and biofilm mechanics*

Biofilms are highly structured, densely packed bacterial consortia. Their structures are often explained as the result of social interactions between bacteria, e.g. cooperation and competition. Others concentrate on the role of local mechanics in biofilm formation. These two lines of argumentation are typically treated separately. Here, we show that mechanics and social interactions can be strongly interrelated and their combination can crucially impact biofilm formation and dynamics. Using Vibrio cholerae strains that kill each other on contact, we examine how bacterial antagonism impacts biofilm mechanics, and vice versa. We find that this interplay leads to counterintuitive results. For example, killing produces dead cells, which can prevent subsequent killing, and, thus, stabilizes coexistence.