DNA-uptake pili of Vibrio cholerae are required for chitin colonisation and capable of kin recognition via sequence-specific self-interaction

How bacteria colonise surfaces and how they distinguish the individuals around them are fundamental biological questions. Type IV pili are a widespread and multi-purpose class of cell surface polymers. Here we directly visualise the DNA-uptake pilus of Vibrio cholerae, which is produced specifically during growth upon its natural habitat - chitinous surfaces. As predicted, these pili are highly dynamic and retract prior to DNA-uptake during competence for natural transformation. Interestingly, DNA-uptake pili can also self-interact to mediate auto-aggregation. This capability is conserved in disease-causing pandemic strains, which typically encode the same major pilin subunit, PilA. Unexpectedly, however, we discovered that extensive strain-to-strain variability in PilA, present in environmental isolates, creates a set of highly specific interactions, enabling cells producing pili composed of different PilA subunits to distinguish between one another. We go on to show that DNA-uptake pili bind to chitinous surfaces, are required for chitin colonisation under flow, and that pili capable of self-interaction connect cells on chitin within dense pili networks. Our results suggest a model whereby DNA-uptake pili function to promote inter-bacterial interactions during surface colonisation. Moreover, they provide evidence that type IV pili could offer a simple and potentially widespread mechanism for bacterial kin recognition.