Overview of Study on Bacillus subtilis Spores

This review documents my research for the past 29 years in the work of bacterial sporulation. The Gram-positive bacterium Bacillus subtilis forms spores when conditions are unsuitable for growth. The mature spores remain for long periods of starvation and are resistant to harsh environment. This property is attributed mainly to the unique figures of spore's outer layers, spore coat. The protein composition of the spores was comprehensively analyzed by a combination of SDS-PAGE and LC-MS/MS. The total of 154 proteins were identified and 69 of them were novel. The expression of the genes encoding them was dependent on sporulation-specific sigma factors, sigma(F), sigma(E), sigma(G) and sigma(K). The expression of a coat protein gene, cotS, was dependent on sigma(K) and GerE. CotE is essential for the assembly of CotS in the coat layer. Many coat genes were identified by reverse genetics and the regulation of the gene expression was studied in detail. Some cot genes are functioned in the resistance to heat and lysozyme, and some of the coat proteins are involved in the specificity of germinants. The yrbA is essential in spore development, yrbA deficient cells revealed abnormal figures of spore coat structure and changed the response to germinants. The location of 16 coat proteins was determined by the observation of fluorescence microscopy using fluorescence-labelled proteins. One protein was assigned to the cortex, nine to the inner coat, and four to the outer coat. In addition, CotZ and CgeA appeared in the outermost layer of the spore coat.