New clusters of genes required for gliding motility in Myxococcus xanthus

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Abstract
Gliding is the directed movement of cells across surfaces which occurs in the absence of external organelles such as flagella. Gliding of the complex prokaryote, Myxococcus xanthus, results from the action of two independent sets of genes known as the A (adventurous motility) and S (social motility) genes. Strains with mutations in both systems (A-S-) do not spread on agar surfaces because both individual and group movement is abolished. To generate regulated, transcriptional fusions with operons including A and S genes, we introduced TN5-lac into A- and S- strains to obtain non-motile A-S::Tn5-lac and A::Tn5-lac S- double mutants. These insertions identify five separate clusters of A genes and three separate clusters of S genes on the M. xanthus genome. Some Tn5-lac insertions map near two of the five previously identified motility gene clusters, but at least five new clusters were identified in this search. Single mutations at only one locus, mglA, block motility; the mglA locus is epistatic to A and S motility genes. A- and S- Tn5-lac insertions were transduced into mgl+ and delta mgl strains. The levels of beta-galactosidase activity produced from each A- or S- Tn5-lac insertion are similar in otherwise isogenic mgl+ and delta mgl strains, showing that MglA does not regulate the transcription of many A and S genes.