GENETIC AND FUNCTIONAL EVIDENCE THAT TYPE-IV PILI ARE REQUIRED FOR SOCIAL GLIDING MOTILITY IN MYXOCOCCUS-XANTHUS

The social gliding behaviour of Myxococcus xanthus has previously been associated with the presence of polar pill. A Tn5 transposon insertio n was isolated which introduces a defect in social gliding and is gene tically linked to a known sgl locus; this insertion was found also to cause a piliation defect. A 2.7 kb section of DNA was isolated from ei ther side of this transposon and sequenced, revealing three genes whic h encode amino acid sequences with substantial similarity to component s of the Type IV pilus biogenesis pathway in Pseudomonas aeruginosa. T he myxococcal pilA gene encodes a putative pilin precursor with a shor t signal sequence and processing site similar to those of other Type I V pilins. Myxococcal pilS and pilR encode amino acid sequences with si milarity to PilS and PilR of P. aeruginosa, as well as to other member s of the NtrB/C family of two-component regulators. Mutations within p ilR and pilA that have no polar effect were demonstrated to be respons ible for pilus and social motility defects. These results indicate tha t the pill of M. xanthus belong to the Type IV family of pill, and dem onstrate that these pill are actually required for social motility.