Selfish bioengineering: How bacterial biofilms collectively defend public goods

Many bacteria in nature exist in biofilms -- surface-associated colonies built around a structural polymer network produced by the embedded cells. This polymer network protects cells against physical and chemical intrusions, giving biofilm-dwelling cells a survival advantage at a significant metabolic cost. Mounting evidence shows that biofilms can also prevent other cells in the environment from joining the collective, even of the same species. However, the mechanism that biofilms use to simultaneously cohere as a colony while excluding invaders is unknown. Using the model biofilm forming species Vibrio cholerae -- the causative agent of the pandemic disease cholera -- we combine confocal microscopy with digital in-line holography to reconstruct three-dimensional trajectories of swimming cells encountering the biofilm and observe failed invasion attempts in real time. Along with complementary biochemical assays, we reveal the multiple layers of defensive strategies engineered by the bacterial biofilm collective.