A spore coat protein, CotS, of Bacillus subtilis is synthesized under the regulation of sigmaK and GerE during development and is located in the inner coat layer of spores.

The spore coat of Bacillus subtilis has a unique morphology and consists of polypeptides of different sizes, whose synthesis and assembly are precisely regulated by a cascade of transcription factors and regulatory proteins. We examined the factors that regulate cotS gene expression and CotS assembly into the coat layer of B. subtilis by Northern blot and Western blot analysis. Transcription of cotS mRNA was not detected in sporulating cells of sigmaK and gerE mutants by Northern blot analysis. By Western blot analysis using anti-CotS antibody, CotS was first detected in protein samples solubilized from wild-type cells at 5 h after the start of sporulation. CotS was not detected in the vegetative cells and spores of a gerE mutant or in the spores of mutants deficient in sigmaE, sigmaF, sigmaG, or sigmaK. CotS was detected in the sporangium but not in the spores of a cotE mutant. The sequence of the promoter region of cotS was similar to the consensus sequences for binding of sigmaK and GerE. These results demonstrate that sigmaK and GerE are required for cotS expression and that CotE is essential for the assembly of CotS in the coat. Immunoelectron microscopic observation using anti-CotS antibody revealed that CotS is located within the spore coat, in particular in the inner coats of dormant spores.