These results suggest that the SigA σ factor could be utilized by RNA polymerase for transcribing the narK2X promoter. However, further experimentation is required to confirm the
possibility. The introduction of M. tb narGHJI or narK2 into M. bovis did not result in an increase in its nitrate reductase activity either under aerobic or hypoxic conditions (Sohaskey & Modesti, 2009). Therefore, it was speculated that the underlying reason for the low LDK378 concentration nitrate reductase activity in M. bovis could be the absence of functional copies of both narGHJI and narK2 genes (Sohaskey & Modesti, 2009). Hence, we complemented M. bovis with both pNarG-GM1 (integrative vector) and pNarK2X (extrachromosomal vector) carrying narGHJI genes and narK2 along with the downstream gene narX gene, respectively. The nitrate reductase activity of M. tb H37Rv was moderate under aerobic conditions and was induced ∼17-fold under hypoxic conditions as expected (Table 4). However, very low aerobic activity Sirolimus cost and no hypoxic induction of nitrate reductase activity were observed in M. bovis or strains harbouring either pNarG-GM1 or pNarK2X or both (Table 4). These results suggest the possibility that robust nitrate reduction in M. tb requires the presence of not merely functional narGHJI and narK2X operons but also some unidentified additional mechanism(s) that is defective
in M. bovis. This notion is supported by the fact that even aerobic nitrate reductase activity of M. bovis was not equivalent to that in the M. tb level despite complementation with M. tb narGHJI here, or as described previously (Sohaskey & Modesti, 2009). A unique NheI restriction site Plasmin (GCTAGC) is created in the 280-bp promoter
region as a consequence of the −6T/C SNP in the narK2X promoter of M. bovis/BCG (Fig. 1). This SNP was exploited to design a new PCR-RFLP assay aimed at differentiating M. tb from M. bovis/BCG. After amplification of the 178-bp narK2X promoter region and NheI-mediated cleavage of the PCR products, two digestion product bands of 120 and 58 bp were observed with DNA from M. bovis AN5 and BCG (vaccine strain, Chennai, India), whereas an intact band of 178 bp was observed with DNA amplified from M. tb (Fig. 2a and b). To further extend the analysis, 36 clinical isolates including M. tb (10), M. bovis (20), BCG (two), M. microti (two) and M. africanum (two) were tested for this RFLP. Except for the M. tb strains, all other MTC member strains produced a two-band pattern and established that the −6T/C SNP is present in all of them. A representative analysis is shown in Fig. 2c. blast analysis of the sequence (http://www.sanger.ac.uk) confirmed the presence of this SNP in M. microti and M. africanum and its absence in Mycobacterium canetti. Two PCR-RFLP methods based on SNPs in gyrB and narGHJI were previously used to differentiate M. tb from MTC members (Niemann et al.