DNA-uptake pilus of Vibrio cholerae capable of kin-discriminated auto-aggregation

Natural competence for transformation is a widely used and key mode of horizontal gene transfer that can foster rapid bacterial evolution. Competent bacteria take-up DNA from their environment using Type IV pili, a widespread and multi-purpose class of cell surface polymers. However, how pili facilitate DNA-uptake has remained unclear. Here, using direct labelling, we show that in the Gram-negative pathogen Vibrio cholerae DNA-uptake pili are abundant, highly dynamic and that they retract prior to DNA-uptake. Unexpectedly, these pili can self-interact to mediate auto-aggregation of cells into macroscopic structures. Furthermore, extensive strain-to-strain variability in the major pilin subunit PilA controls the ability to aggregate without affecting transformation, and enables cells producing pili composed of different PilA to discriminate between one another. Our results suggest a model whereby DNA-uptake pili function to promote inter-bacterial interactions during surface colonisation and moreover, reveal a simple and potentially widespread mechanism for bacterial kin recognition.