Characterization of a new sigma-K-dependent peptidoglycan hydrolase gene that plays a role in Bacillus subtilis mother cell lysis

Bacillus subtilis produces a 30-kDa peptidoglycan hydrolase, CwlH, during the late sporulation phase. Disruption of yqeE led to a complete loss of CwlN formation, indicating the identity of yqeE with cwlH. Northern blot analysis of cwlH revealed a 0.8-kb transcript after 6 to 7.5 h fur the wild-type strain but not for the sigma(F), sigma(E), sigma(G), and sigma(K) mutants. Expression of the sigma(K)-dependent cwlH gene depended on gerE. Primer extension analysis also suggested that cwlH is transcribed by E sigma(K) RNA polymerase. CwlH produced in Escherichia coli harboring a cwlH plasmid is an N-acetylmuramoyl-L-alanine amidase (EC 3.5.1.28) and exhibited an optimum pH of 7.0 and high-level binding to the B. subtilis cell wall. A cwlC cwlH double mutation led to a lack of mother cell lysis even after 7 days of incubation in DSM medium, but the single mutations led to mother cell lysis after 24 h.