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Journal of Bacteriology, April 2003, p. 2635-2643, Vol. 185, No. 8
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.8.2635-2643.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

The Staphylococcus aureus cidAB Operon: Evaluation of Its Role in Regulation of Murein Hydrolase Activity and Penicillin Tolerance

Kelly C. Rice, Brian A. Firek, Jeremy B. Nelson, Soo-Jin Yang, Toni G. Patton, and Kenneth W. Bayles*

Department of Microbiology, Molecular Biology and Biochemistry, University of Idaho, Moscow, Idaho 83844-3052

Received 11 November 2002/ Accepted 31 January 2003

Recent studies have shown that expression of the Staphylococcus aureus lrgAB operon inhibits murein hydrolase activity and decreases sensitivity to penicillin-induced killing. It was proposed that the lrgAB gene products function in a manner analogous to an antiholin, inhibiting a putative holin from transporting murein hydrolases out of the cell. In the present study the cidAB operon was identified and characterized based on the similarity of the cidA and cidB gene products to the products of the lrgAB operon. Zymographic and quantitative analyses of murein hydrolase activity revealed that mutation of the cidA gene results in decreased extracellular murein hydrolase activity compared to that of S. aureus RN6390, the parental strain. Complementation of cidA expression restored the wild-type phenotype, indicating that expression of the cidAB operon has a positive influence on extracellular murein hydrolase activity. The cidA mutant also displayed a significant decrease in sensitivity to the killing effects of penicillin. However, complementation of the cidA defect did not restore penicillin sensitivity to wild-type levels. Reverse transcriptase PCR also revealed that cidAB is maximally expressed during early exponential growth, opposite of what was previously observed for lrgAB expression. Based on these results, we propose that the cidAB operon encodes the holin-like counterpart of the lrgAB operon and acts in a manner opposite from that of lrgAB by increasing extracellular murein hydrolase activity and increasing sensitivity to penicillin-induced killing.


* Corresponding author. Mailing address: Department of Microbiology, Molecular Biology and Biochemistry, College of Agriculture, University of Idaho, Moscow, ID 83844-3052. Phone: (208) 885-7164. Fax: (208) 885-6518. E-mail: kbayles{at}uidaho.edu.


Journal of Bacteriology, April 2003, p. 2635-2643, Vol. 185, No. 8
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.8.2635-2643.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.




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