epidermidis, consistent with the finding for S. aureus. Further analysis of the microarray data showed that genes upregulated in the 1457ΔlytSR strain included these involved in purine biosynthesis (pur; SERP0651-SERP0657), amino acid Angiogenesis inhibitor biosynthesis (leu; SERP1668-SERP1671,

hisF, argH, gltB) and membrane transport (oppC, modC, gltS, putP, SERP0284, SERP0340, etc.). Whereas, genes downregulated contained these involved in pyruvate metabolism (mqo-2, SERP2169 and mqo-3), anaerobic growth (nar; SERP1985-SERP1987, arc; SE0102-SE0106) (Table 1). In addition, genes responsible for encoding ribosomal proteins which make up the ribosomal subunits in conjunction with rRNA were found to be downregulated in 1457ΔlytSR (Table 1), consistent with that reported in transcriptional profiling studies of S. aureus by Sharma et al. [11]. A1155463 Transcription of lrgAB decreased drastically in 1457ΔlytSR, indicating that the operon was activated by LytSR in S.epidermidis, consistent with the finding for S. aureus. We also noticed that expression of an AraC family transcriptional regulator homologue was remarkably higher in the mutant (Table 1). The microarray experiments were repeated by Prof. Jacques Schrenzel (Genomic Research Laboratory, University of Geneva Hospitals, Switzerland). Transcription of genes required for amino acid biosynthesis, carbon metabolism and membrane transport was also found to be altered in the mutant.

Moreover, differential expression of general stress protein, alkaline shock protein 23 and cold

shock protein was observed in the latter microarray data. Glutathione peroxidase Taken together, it suggested that LytSR may be involved in sensing and responding to changes in the metabolic state of the bacteria. Table 1 Genes expressed differentially in strain 1457ΔlytSR compared to the wild-type strain ORF Gene name Description or predicted function Expression ratio (Mutant/WT) Amino acid biosynthesis SERP0034 metE 5-methyltetrahydropteroyltriglutamate homocysteine methyltransferase 2.096 SERP0108 gltB glutamate synthase large subunit 2.405 SERP0548 argH argininosuccinate lyase 5.03 SERP1103 aroK shikimate kinase 2.274 SERP1668 ilvC ketol-acid reductoisomerase 2.087 SERP1669 leuA 2-isopropylmalate synthase 2.344 SERP1670 leuB 3-isopropylmalate dehydrogenase 2.229 SERP1671 leuC 3-isopropylmalate dehydratase small subunit 11.45 SERP2301 hisF imidazoleglycerol phosphate synthase, cyclase subunit 5.429 Amino acid transport SERP0392   di-tripeptide transporter, putative 3.362 SERP0571 oppC oligopeptide transport system permease protein OppC 12.38 SERP0950   peptide ABC transporter, ATP-binding protein, putative 3.383 SERP1440 putP proline permease 2.124 SERP1935 gltS sodium:glutamate symporter 3.267 Inorganic ion transport and metabolism SERP0284   Na+/H+ antiporter, MnhD component, putative 3.294 SERP0287   Na+/H+ antiporter, MnhG component, putative 2.576 SERP0660   cobalt transport family protein 2.718 SERP1777   iron compound ABC transporter, iron 2.