SpxB regulates O-acetylation dependent resistance of Lactococcus lactis peptidoglycan to hydrolysis

Endogenous peptidoglycan (PG) hydrolysing enzymes, the autolysins, are needed to relax the rigid PG sacculus to allow bacterial cell growth and separation. PG of pathogens and commensal bacteria may also be degraded by hydrolases of animal origin (lysozymes), which act as antimicrobials. The genetic mechanisms regulating PG resistance to hydrolytic degradation was dissected in the Gram-positive bacterium Lactococcus lactis. We found that the ability of L. lactis to counteract PG hydrolysis depends on the degree of acetylation. Overexpression of PG O-acetylase, encoded by oatA, led to bacterial growth arrest, indicating potential lethality of oatA and a need for its tight regulation. A novel regulatory factor SpxB (previously denoted as YneH), exerts a positive effect on oatA expression. Our results indicate that SpxB binding to RNA polymerase constitutes a previously missing link in the multi-step response to cell envelope stress, provoked by PG hydrolysis with lysozyme. We suggest that the two component system CesSR responds to this stress by inducing SpxB, thus favoring its interactions with RNA polymerase. Induction of PG O-acetylation by this cascade renders it resistant to hydrolysis. Keywords: mutant, lysozym RNA was isolated from 3 independent cultures of L. lactis MG1363/pVE3916 (VES4075) and L. lactis MG1363/pspxB+ (VES3910). Slide data were processed and normalized using MicroPrep software as described in this article. Expression of a gene was considered to be significantly altered when the Cyber T baysian P-value 0.001.