MUTATIONS AFFECTING GERMINATION IN MYXOCOCCUS-XANTHUS

Myxococcus xanthus mutants defective in myxospore germination have been isolated both by a selective and by a non-selective method after UV or Tn5-lac-induced mutagenesis. The ability of these mutants to germinate in germinant solutions other than those used for their isolation has been tested. Six of seven mutants isolated behaved as germination-defective in all germinants. Germination of the seventh mutant was conditional on the germinant used, being normal in Casamino acids but defective in a Casitone-based medium. Genetic analysis of the four mutant strains carrying Tn5-lac insertions revealed that the transposon had disrupted a different locus in each mutant, so that the four mutants defined four unlinked loci involved in the germination process (gerA, gerB, gerC, gerD). Strain MR307 was studied in more detail. Cloning of the gene affected in this mutant, gerC, and construction of merodiploids revealed that the wild-type allele is dominant over the mutated one. In vitro construction of lacZ fusions allowed study of gerC expression throughout the M. xanthus life cycle, revealing that the gene affected by insertion at OMEGA-MR307 is developmentally regulated.