A Tad pilus promotes the establishment and resistance of biofilms to mechanical clearance.

is autochthonous to estuaries and warm coastal waters. Infection occurs via open wounds or ingestion, where its asymptomatic colonization of seafood, most infamously oysters, provides a gateway into the human food chain. Colonization begins with initial surface contact, which is often mediated by bacterial surface appendages called pili. Type IV Tad pili are widely distributed in the Vibrionaceae, but evidence for a physiological role for these structures is scant. The genome codes for three distinct loci. Recently, a positive correlation was demonstrated between the expression of and the phenotypes of a descendent (NT) that exhibited increased biofilm formation, auto-aggregation, and oyster colonization relative to its parent. However, the mechanism by which pilus expression promoted these phenotypes was not determined. Here, we show that deletion of the pilin gene () altered the near-surface motility profile of NT cells from high curvature, orbital retracing patterns characteristic of cells actively probing the surface to low curvature traces indicative of wandering and diminished bacteria-surface interactions. The NT pilin mutant also exhibited decreased initial surface attachment, attenuated auto-aggregation and formed fragile biofilms that disintegrated under hydrodynamic flow. Thus, the locus, designated , promoted nitial surface attachment, uto-aggregation and resistance to echanical clearance of biofilms. The prevalence of loci in the Vibrionaceae suggests that they may play equally important roles in other family members.