Characterization of Putative Sporulation and Germination Genes in Food-Poisoning Strain SM101.

Bacterial sporulation and spore germination are two intriguing processes that involve the expression of many genes coherently. Phylogenetic analyses revealed gene conservation among spore-forming Firmicutes, especially in Bacilli and Clostridia. In this study, by homology search, we found sporulation gene homologs of , , , , , , , and in food-poisoning Type F strain SM101. The β-glucuronidase reporter assay revealed that promoters of six out of eight tested genes (i.e., , , , , , and ) were expressed only during sporulation, but not vegetative growth, suggesting that these genes are sporulation-specific. Gene knock-out studies demonstrated that Δ, Δ, Δ, and Δ mutant strains produced a significantly lower number of spores compared to the wild-type strain. When the spores of these six mutant strains were examined for their germination abilities in presence of known germinants, an almost wild-type level germination was observed with spores of Δ or Δ mutants; and a slightly lower level with spores of Δ or Δ mutants. In contrast, almost no germination was observed with spores of Δ or Δ mutants. Consistent with germination defects, Δ or Δ spores were also defective in spore outgrowth and colony formation. The germination, outgrowth, and colony formation defects of Δ or Δ spores were restored when Δ or Δ mutant was complemented with wild-type or , respectively. Collectively, our current study identified new sporulation and germination genes in .