, 2011). The preferential binding of DevRS1 peptide-displaying phage (G43) to the DevR C-terminal domain (Fig. 1b) and inhibition of Rv3134c promoter activity suggested the possibility that DevRS1 peptide prevents DevR binding to DNA. However, DevRS1 failed to inhibit the DNA binding activity of DevR in an in vitro electrophoresis mobility shift assay (not shown). The peptide also did not inhibit phosphorylation of DevR, which is essential for its sequence-specific binding to DNA (not shown). The detailed mechanism this website of DevRS1 peptide-mediated

inhibition of DevR function needs to be deciphered. DevRS1 was also noted to inhibit the viability of DevRS1-treated M. tb cultures; hypoxic viability was reduced by 88% and 94% in the presence of 2.5 and 5 mM peptide in the CFU assay (Fig. 2b, left panel) and by 82% and 89% in the HyRRA with respect to DMSO control (Fig. 2b, right panel). By contrast, the viability of DevRS1-treated aerobic M. tb cultures was only moderately reduced (by 50% in the CFU assay Fig. 2b, left panel and ~ 10–30% in REMA Fig. 2b, right panel). As HyRRA and not the CFU assay truly reports the viability of drug-treated dormant cultures (Taneja & Tyagi, 2007), it is evident that DevRS1 kills hypoxia-adapted dormant bacteria more efficiently as compared to aerobic cultures. In the HyRRA setup, anaerobic condition (assessed by methylene blue decolorization)

is established by day check details 30 at which time the peptide was added to the cultures and incubated further for 5 days. From the inhibitor experiment in the HyRRA model, it is evident that DevR function is required for hypoxic viability beyond day 30 and our findings are consistent with earlier reports (Voskuil et al., 2003; Leistikow et al.,

2010). Plausible reasons for the lack of consistency between the two assays (50–60% inhibition in reporter assay vs. 94% inhibition in the viability assay) include (1) the reporter assay Carbohydrate measures a single parameter, that is, Rv3134c promoter activity, whereas viability is an outcome of multiple factors, and (2) the partial inhibition of promoter activity likely results in suboptimal concentrations of DevR protein thereby leading to a defect in dormancy adaptation and hence hypoxic viability. This is consistent with the requirement of an adequate level of DevR for M. tb viability under hypoxia (Majumdar et al., 2010). DevRS1 peptide was assessed next for its cytotoxicity using two cell lines namely, HEK293 (human embryonic kidney cells) and HepG2 (human liver hepatocellular carcinoma cell line). In the presence of DevRS1 peptide, cytotoxicity ranged between 8–12% and 11–27% at 2.5 and 5 mM peptide concentration in HepG2 and HEK293 cells, respectively (data not shown). The ability of DevRS1 peptide, albeit at high concentrations, to inhibit DevR-dependent gene expression and hypoxic viability demonstrates the crucial role of DevR in adaptation under hypoxia-induced dormancy.