Joint Research on Myxobacterial Development

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Myxobacteria are unique gram-negative bacteria which undergo multicellular development. When nutrients are depleted in a solid medium, cells aggregate to form mounds which eventually convert to fruiting bodies. Rod-shaped cells differentiate to round or ovoid spores. During the development of Myxococcus xanthus, five cycles of intercellular signal exchanges are known to occur. The fruA gene encodes a putative 25-kDa transcription factor essential for the development of M.xanthus. In the present study, we have demonstrated the presence of a putative repressor X for fruA expression by gel shift experiments. Binding competition experiments suggested the X recognition sequence. Structure of protein P15, expression of which was inhibited by the fruA mutation, was analyzed by mass spectroscopy. Insertion of kanamycin-resistance DNA fragment into ORF134 resulted in failure of development, suggesting the presence of ORF134-fruB operon responsible for M.xanthus development. Two promoter structures were found for this operon : One promoter works during vegetative growth, while both two promoters work during development. M.xanthus lonD was found to be a heat shock gene. Expression of lonD was independent on sigBCE genes encoding an Escherichia coli RpoH homolog, but dependent on hsfA and sigA encoding a RpoD homolog. The hsfA gene encodes a putative effecter of a two-component system, which was phosphorylated by HsfB kinase. Phosphorylated-HsfA bound to promoter sequence for lonD gene. M.xanthus carries at least 13 eukaryotic-like protein Ser/Thr pkn kinases. Many gene products were found to interact with Pkn kinases by two-hybrid experiments.