Abstract: Bacterial type IV pili or pilus (T4P) not only plays an important role in such biological processes as biofilm formation, DNA intake and bacterial pathogenesis but also enables bacterial motility on solid surfaces. Despite its importance, we know very little about the assembly mechanism among T4P proteins of Myxococcus xanthus.Deletion and supplement experiments of single gene pilN/O/P/Q demonstrate that strain removal causes Myxococcus xanthus colony to totally lose social motility, but strain supplement can restore their social motility. We employed yeast two hybrid (Y2H) to detect the interactions among M. xanthus T4P proteins. We discovered that PilP at periplasm interacted not only with C end of outerfilm protein PilQ, but also with innerfilm protein PilO. Results of yeast two hybrid (Y2H) and genetics experiments show that protein PilP is the bridge connecting innerfilm and outerfilm. This indicates that proteins PilN/O/P/Q may form a total complex including periplasm, innerfilm and outerfilm, and play an important role in pilus extension and contraction. Our research lays a solid foundation for the exploration of molecular mechanism of the extension and contraction of Myxococcus xanthus pilus.

Key words: Myxococcus xanthus, yeast two hybrid, type IV pili, social motility