A Vibrio vulnificus type IV pilin contributes to biofilm formation, adherence to epithelial cells, and virulence

Vibrio vulnificus expresses a multitude of cell-associated and secreted factors that potentially contribute to pathogenicity, although the specific roles of most of these factors have been difficult to define. Previously we have shown that a mutation in pilD (originally designated vvpD), which encodes a type IV prepilin peptidase/N-methyltransferase, abolishes expression of surface pili, suggesting that they belong to the type IV class. In addition, a pilD mutant exhibits reduced adherence to HEp-2 cells, a block in secretion of several exoenzymes that follow the type II secretion pathway, and decreased virulence. In this study, we have cloned and characterized a V. vulnificus type IV pilin (PilA) that shares extensive homology to group A type W pilins expressed by many pathogens, including Vibrio cholerae (PilA), Pseudomonas aeruginosa (PiIA), and Aeromonas hydrophila (TapA). The V. vulnificus pil4 gene is part of an operon and is clustered with three other pilus biogenesis genes, pilBCD. Inactivation of pil4 reduces the ability of V. vulnificus to form biofilms and significantly decreases adherence to HEp-2 cells and virulence in iron dextran-treated mice. Southern blot analysis demonstrates the widespread presence of both pil4 and pilD in clinical as well as environmental strains of V. vulnificus.