ABSTRACT
Three independent Tn5-lac insertions in the S1 locus ofMyxococcus xanthus inactivate the sglK gene, which is nonessential for growth but required for social motility and multicellular development. The sequence of sglK reveals that it encodes a homologue of the chaperone HSP70 (DnaK). ThesglK gene is cotranscribed with the upstreamgrpS gene, which encodes a GrpE homologue. UnlikesglK, grpS is not required for social motility or development. Wild-type M. xanthus is encased in extracellular polysaccharide filaments associated with the multimeric fibrillin protein. Mutations in sglK inhibit cell cohesion, the binding of Congo red, and the synthesis or secretion of fibrillin, indicating that sglK mutants do not make fibrils. ThefibR gene, located immediately upstream of thegrpS-sglK operon, encodes a product which is predicted to have a sequence similar to those of the repressors of alginate biosynthesis in Pseudomonas aeruginosa andPseudomonas putida. Inactivation of fibR leads to the overproduction of fibrillin, suggesting that M. xanthus fibril production and Pseudomonas alginate production are regulated in analogous ways. M. xanthus andPseudomonas exopolysaccharides may play similar roles in a mechanism of social motility conserved in these gram-negative bacteria.
ADP‐ribosylation by the extracellular fibrils of
Myxococcus xanthus