Functional Analysis of the Major Pilin Proteins of Type IV Pili in CGMH010.

The gene cluster for Type IV pilus (Tfp) biosynthesis is commonly present and highly conserved in . Nevertheless, Tfp-mediated twitching motility is less common among strains, and the factors determining twitching activity are not fully understood. Here, we analyzed the functions of three major pilin proteins (PilA1, PilA2, and PilA3) in the assembly and activity of Tfp in motile CGMH010. Using various recombinant deletion strains, we found that Tfp composed of different PilA proteins varied morphologically and functionally. Among the three PilA proteins, PilA1 was most critical in the assembly of twitching-active Tfp, and recombinant strains expressing motility generated more structured biofilms under constant shearing forces compared to the non-motile recombinant strains. Although PilA1 and PilA3 shared 94% identity, PilA3 could not compensate for the loss of PilA1, suggesting that the nature of PilA proteins plays an essential role in twitching activity. The single deletion of individual genes had little effect on the invasion of host endothelia by CGMH010. In contrast, the deletion of all three genes or , encoding the retraction ATPase, abolished Tfp-mediated invasion. Tfp- and PilT-dependent invasion were also detected in the non-motile SK36, and thus, the retraction of Tfp, but not active twitching, was found to be essential for invasion.