Under low-oxygen and aerated cultures, stationary phase induction of lrgAB expression was dramatically reduced when grown in 45 mM glucose, and similar levels of expression were observed in the wild-type and lytS mutant (Figure 1B), suggesting that growth in high levels of GW4869 manufacturer glucose abrogates oxygen-dependent regulation of lrgAB by LytST. Consistent with previously-published data [37], LytS did not appear to have a measurable effect on cidAB expression under any of the growth

conditions tested here (data not shown). In summary, LytST-dependent regulation of lrgAB expression is much more pronounced during low-oxygen growth and at low glucose levels. Figure 1 LytS-dependent expression of lrgAB in S . mutans AMN-107 cell line . Overnight cultures Gemcitabine chemical structure were diluted in THYE, containing either 11 mM (A) or 45 mM glucose (B) to an OD600 = 0.02 and grown at 37°C as static cultures at 5% CO2 (“low-O2”) or as aerobic shaking cultures at 250 RPM (“aerobic”). RNA was harvested at exponential (EP) and stationary phase (SP). Reverse-transcription, real-time PCR reactions, and determination of copy number were performed as described previously using lrgA and 16S-specific primers [37, 77]. Fold-change expression of lrgAB and 16S under each growth condition was calculated

by dividing the gene copy number of each test sample by the average gene BCKDHB copy number of UA159 EP. Data was then normalized by dividing each lrgAB fold-change value by its corresponding 16S fold-change expression value. Data represent the average of 3 biological replicates. Dark grey

bars represent UA159 and light grey bars represent lytS mutant. Error Bars represent the standard error (SEM). Microarray analysis of the LytS regulon Based on the transcriptional data presented above, the effects of LytST regulation on lrgAB expression are most evident while S. mutans is growing under conditions of low-oxygen (5% CO2) with a lower concentration of glucose. To begin to explore how LytST impacts critical phenotypes of S. mutans, RNA expression profiles in UA159 and the lytS mutant were compared using an RNA microarray approach. RNA was isolated from early exponential and late exponential growth phases from static planktonic cultures grown in BHI (containing 11 mM total glucose) at 37°C in a 5% CO2 atmosphere (Additional file 1: Table S1 and Additional file 2: Table S2). At early exponential growth phase, loss of LytS affected the expression of 40 genes (12 upregulated and 28 downregulated; P < 0.005; Additional file 1: Table S1). Most of the upregulated genes in early exponential phase displayed only a modest increase in expression and included genes involved in DNA repair, purine/pyrimidine metabolism, competence, and a number of unassigned and hypothetical ORFs.