Effect of mechanical removal of pili on gliding motility of Myxococcus xanthus.

Gliding motility of Myxococcus xanthus is governed by both the adventurous (A) and the social (S) motility gene systems. The presence of pili has previously been shown to be correlated with a genetically intact S-motility system (D. Kaiser, Proc. Natl. Acad. Sci. USA 76:5952-5956, 1979). The purpose of the present work was to study the direct effect of mechanical removal of pill on the social motility of M. xanthus. Depiliation resulted in (i) a loss of streaming motility of A- S+ mutants, i.e., strains which are able to move by virtue of the S-motility system only, (ii) no effect on motility in A+ S- mutants, i.e., strains capable of movement by the A-motility system only, and (iii) a retardation of streaming speed in the wild-type strain (A+ S+). Cell-cell cohesion, another characteristic of social behavior, was not affected by mechanical removal of pill. The observation that mechanical depiliation perturbed the motility of strains which rely on the S-motility system strongly supports a role for pili in social motility of M. xanthus.