1% yeast extract, 34 mM NaCl, 0.05% sodium thioglycollate, 1 mM MgSO4, 0.1 M MnSO4, buffered to pH 7.3 with 3-(N-morpholino)propanesulfonic acid (MOPS) buffer and supplemented

with 0.1% (w/v) glucose (Fernández et al., 2002). Overnight cultures UK-371804 cost were diluted 1 : 5 in MBB medium and grown until an OD600 nm of approximately 0.4 was reached. Cells were harvested by centrifugation, washed twice with cold buffer A (50 mM MOPS, 50 mM KPO4, 10 mM MgSO4), resuspended in cold buffer A to a final OD600 nmc. 4.0, and kept on ice until used for transport assay. The assay mixtures contained cell suspension (c. 109 CFU mL−1), 1% glucose, and 0.1 mg mL−1 chloramphenicol. Reaction mixtures were preincubated for 10 min at 37 °C prior to the addition of substrates. At time zero, l-[14C]cystine and cold l-cystine were added at a concentration of

4 μM (2.6 mCi mmol−1) and 200 μM, respectively, and the reaction selleck products mixtures were incubated at 37 °C. Samples (100 μL) were removed at regular intervals and immediately filtered through 0.22-μm pore-size membranes. The filters were washed twice with 0.5 mL of buffer A and transferred to vials containing 5 mL of a scintillation fluid for determination of radioactivity. All transport assays were carried out using three independent cultures, and each time point was sampled in duplicate. The specificity of CysBPA-mediated amino acid uptake was also examined using an amino acid competition assay. Uptake of l-[14C]cystine (4 μM) was measured in the presence of 400 μM of the following unlabeled l-amino acids: arginine, cysteine, glutamine, glutamate, leucine, and methionine. As a positive control and to determine total l-[14C] cystine uptake, cells were incubated with 400 μM radio-labeled cystine with no competing substrate. Another control reaction containing no cells was incubated with l-[14C] cystine, and no radioactivity was detected. Overnight cultures were diluted 1 : 20 in triplicate into sterile microtitre plates containing modified minimal medium these (MM) (56 mM glucose, 13.6 mM l-glutamic acid, 7 mM l-leucine, 19 mM

NH4Cl, 20 mM K2HPO4, 11 mM KH2PO4, 50 mM NaHCO3, 4.9 mM MgSO4·7H2O, 0.1 mM MnCl2·4H2O, 72 μM FeSO4·7 H2O, 5.5 mM sodium pyruvate, 2.6 μM riboflavin, 1.4 μM thiamine–HCl, 0.4 μM biotin, 8 μM nicotinic acid, 0.7 μM ρ-aminobenzoic acid, 1 μM calcium pantothenate, and 5 μM pyridoxal–HCl) and buffered with 0.05 M Tris–maleate (pH 7.4) to a final pH of 7.1 (Fujiwara et al., 1978), and modified MM supplemented with 1 mM l-cystine (MMC). Growth kinetics were monitored using a Bioscreen C automated growth reader (Lab Systems), and optical density measurements obtained at 600 nm were plotted against time to obtain growth curves for each strain in specific growth medium. To determine the effects of l-cystine starvation on S. mutans tcyA, tcyB, tcyC transcription, quantitative real-time PCR was performed using the following primers listed in 5′–3′ direction.