Transcriptional Activation of the tad Type IVb Pilus Operon by PypB in Yersinia enterocolitica

Type IV pili are virulence factors in various bacteria and mediate, among other functions, the colonization of diverse surfaces. Various subclasses of type IV pili have been identified, but information on pilus expression, biogenesis, and the associated phenotypes is sparse for the genusYersinia . We recently described the identification of PypB as a transcriptional regulator inYersinia enterocolitica . Here we show that thepypB gene is associated with thetad locus, a genomic island that is widespread among bacterial and archaeal species. The genetic linkage ofpypB with thetad locus is conserved throughout the yersiniae but is not found among other bacteria carrying thetad locus. We show that the genes of thetad locus form an operon inY. enterocolitica that is controlled by PypB and thatpypB is part of this operon. Thetad genes encode functions necessary for the biogenesis of the Flp subfamily of type IVb pili initially described forAggregatibacter actinomycetemcomitans to mediate a tight-adherence phenotype. InY. enterocolitica , the Flp pilin protein shows some peculiarities in its amino acid sequence that imply similarities as well as differences compared to typical motifs found in the Flp subtype of type IVb pili. Flp is expressed and processed after PypB overproduction, resulting in microcolony formation but not in increased adherence to biotic or abiotic surfaces. Our data describe the transcriptional regulation of thetad type IVb pilus operon by PypB inY. enterocolitica but fail to show most previously described phenotypes associated with this type of pilus in other bacteria.