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Abstract:
Biofilms are social entities where bacteria live in tightly packed agglomerations, surrounded
by self-secreted exopolymers. Since production of exopolymers is costly and potentially
exploitable by non-producers, mechanisms that prevent invasion of non-producing mutants
are hypothesized. Here we study long-term dynamics and evolution in Bacillus subtilis biofilm
populations consisting of wild-type (WT) matrix producers and mutant non-producers.
We show that non-producers initially fail to incorporate into biofilms formed by the WTcells,
resulting in 100-fold lower final frequency compared to the WT. However, this is modulated in
a long-term scenario, as non-producers evolve the ability to better incorporate into biofilms,
thereby slightly decreasing the productivity of the whole population. Detailed molecular
analysis reveals that the unexpected shift in the initially stable biofilm is coupled with newly
evolved phage-mediated interference competition. Our work therefore demonstrates
how collective behaviour can be disrupted as a result of rapid adaptation through mobile
genetic elements.