Efficient spore synthesis in Bacillus subtilis depends on the CcdA protein

CcdA is known to be required for the synthesis of c-type cytochromes in Bacillus subtilis, but the exact function of this membrane protein is not known. We show that CcdA also plays a role in spore synthesis. The expression of ccdA and the two downstream genes yneI and yneJ was analyzed. There is a promoter for each gene, but there is only one transcription terminator, located after the yneJ gene. The promoter for ccdA was found to be weak and was active mainly during the transition from exponential growth to stationary phase. The promoters for yneI and yneJ were both active in the exponential growth phase. The levels of the CcdA and YneJ proteins in the membrane were consistent with the observed promoter activities. The ccdA promoter activity was independent of whether the ccdA-yneI-yneJ gene products were absent or overproduced in the cell. It is shown that the four known cytochromes c in B. subtilis and the YneI and YneJ proteins are not required for sporulation. The combined data from analysis of sporulation-specific sigma factor activity, resistance properties of spores, and spore morphology indicate that CcdA deficiency affects stage V in sporulation. We conclude that CcdA, YneI, and YneJ are functionally unrelated proteins and that the role of CcdA in cytochrome c and spore synthesis probably relates to sulfhydryl redox chemistry on the outer surface of the cytoplasmic membrane.