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7 The Frz Chemosensory System of Myxococcus xanthus
Myxococcus xanthus has attracted much scientific interest because of its complex life cycle and morphogenetic potential. Western blot analysis showed that vegetative cells are highly methylated (about 50% of FrzCD is methylated) but cells that are starved are relatively unmethylated. The methylation changes in FrzCD suggest that during aggregation, FrzCD senses a chemical(s) produced by other cells that promotes cell movements towards aggregation centers. S-motility in M. xanthus, like twitching motility in Pseudomonas aeruginosa, has been shown to involve the extension and retraction of type IV pili localized at the leading cell pole. The stimulatory mutations blocked both vegetative swarming and developmental aggregation. The inhibitory mutations blocked developmental aggregation at low cell density, but not at high cell density, suggesting that specific methylation sites may be required for sensing low concentrations of developmental signals. The different phenotypes of the mutants observed in this study suggest that differential methylation could provide a potential signal input to the Frz chemosensory pathway. FrzS was also studied by constructing in-frame deletion mutants that express stable cryptic proteins; these mutants showed loss of function and/or distinct localization defects. Specifically, in-frame deletions of the pseudoreceiver domain, the coiled-coil domain, and a motif located at the very C terminus of the protein each resulted in aberrant localization and loss of function defects.
Key Concept Ranking
- Type IV Pili