13 Composition, Structure, and Function of the Myxococcus xanthus Cell Envelope

This chapter covers in detail the polysaccharide-containing components of the Myxococcus xanthus cell envelope including the peptidoglycan (PG), lipopolysaccharide (LPS), extracellular matrix (ECM), and capsular exopolysaccharide (EPS). First, the PG was associated with substantial amounts of glycine, serine, and glucose. Second, the vegetative cell wall PG was suggested to be discontinuous in that whole sacculi were not isolated and trypsin and sodium dodecyl sulfate were able to completely disassociate the PG. At least two factors regulate MBHA accumulation. First, mbhA transcription, which is σ-54 dependent, increases during development. Second, the stability of the mbhA mRNA is increased during development. Interestingly, all of the LPS mutants identified by the authors' two laboratories mapped to three loci: two LPS O-antigen loci and one LPS core locus. The carbohydrate composition of wild-type LPS consists of glucose, mannose, rhamnose, arabinose, xylose, galactosamine, glucosamine, KDO (2-keto-3-deoxyoctulosonic acid), and 3-O-methylpentose and 6-O-methylgalactosamine. Signal perception by the Dif pathway involves Tfp. First, Tfp was found to be required for EPS production in M. xanthus. Second, Dif proteins function downstream of Tfp as demonstrated by genetic epistasis tests. Finally, Tfp do not appear to function as either exogenous or endogenous signals for the Dif pathway. Preliminary biochemical studies indicated that M. xanthus EPS contains at least five monosaccharides: galactose, glucosamine, glucose, rhamnose, and xylose. Studies of M. xanthus pili focus on their involvement in S-motility.