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Conditional Mutation of an Essential Putative Glycoprotease Eliminates Autolysis in Staphylococcus aureus

Department of Veterinary and Biomedical Sciences, College of Veterinary Medicine, University of Minnesota, 1971 Commonwealth Ave., St. Paul, Minnesota 55108,¹ Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, Nebraska 68198-6495,² Laboratory of Microbial Biofilms, Instituto de Agrobiotecnologia, Universidad Publica de Navarra, Pamplona 31006, Spain³

Received 30 November 2006/ Accepted 9 January 2007

Our previous studies demonstrated that a putative Staphylococcus aureus glycoprotease (Gcp) is essential for bacterial survival, indicating that Gcp may be a novel target for developing antibacterial agents. However, the biological function of Gcp is unclear. In order to elucidate the reason that Gcp is required for growth, we examined the role of Gcp in bacterial autolysis, which is an important biological process for bacterial growth. Using both a spacp-regulated gcp expression strain and a TetR-regulated gcp antisense expression strain, we found that the down-regulation of gcp expression can effectively inhibit Triton X-100-induced lysis, eliminate penicillin- and vancomycin-caused cell lysis, and dramatically increase tolerance to hydrolases. Moreover, we determined whether resistance to lysis is due to a defect in murein hydrolase activity by using a zymogram analysis. The results showed that the cell lysate of a down-regulated gcp expression mutant displayed several bands of decreased murein hydrolytic activity. Furthermore, we explored the potential mechanism of Gcp's involvement in autolysis and demonstrated that Gcp may function independently from several key autolysins (Atl, LytM, and LytN) and regulators (ArlRS, Mgr/Rat, and CidA). Taken together, the above results indicate that the essential Gcp is involved in the modification of substrates of murein hydrolases as well as in the regulation of expression and/or activity of some murein hydrolases, which, in turn, may play important roles in bacterial viability.

Published ahead of print on 19 January 2007.