Although the expression levels of the eight genes were 0.17–0.63-fold in the ΔsdrP strain relative to that in wild type, their q-values except that of TTHA1128 were 0.061–0.242, which were greater than the threshold value used in the experiment (0.06). As for TTHA1128, identification of a SdrP-binding site in the promoter region was missed in the previous study. Conversely, expression of four out of 14 SdrP-regulated genes identified in the previous study showed lower correlation to that of sdrP (Spearman’s correlation

coefficients≤0.51). Some unknown factors such as promoter activity and affinity of SdrP to DNA in vivo, and unidentified transcriptional regulator(s) that might act together with SdrP, might influence the results of the experimental screenings for SdrP-regulated Selleckchem RO4929097 genes. Thus, a combination of comparative expression analysis and expression pattern analysis was appropriate for screening of SdrP-regulated genes. Among the environmental and chemical stresses examined in this study, the diamide and H2O2 stresses were the

most effective in enhancing the expression of sdrP and its target genes in the wild-type strain. Furthermore, an excess amount of CuSO4 was JAK inhibitor a strong inducer of sdrP gene expression in the ΔcsoR strain, in which excess Cu(I) ions may accumulate (Sakamoto et al., 2010). In this strain, excess Cu(I) ions, which have the potential to drive oxidation/reduction to form free radicals (Touati, 2000; Imlay, 2002), may trigger expression of sdrP. As for the possible cellular functions of the 22 SdrP-regulated gene products, at least nine, i.e. TTHA0425, TTHA0557, TTHA0654, TTHA0986, TTHA1028, TTHA1215, TTHA1625, TTHA1635, and TTHB132, are possibly involved in redox control (Table 2) (Agari et al., 2008). UvrB (TTHA1892) Ergoloid may be involved in the repair of oxidized DNA. The altered expression levels of sdrP and its target genes in the stationary growth phase were similar to those caused by diamide treatment. These

results suggest that the main inducer of sdrP expression is oxidative stress, and support the previous finding that SdrP functions in the response to oxidative stress. Because SdrP does not have a cysteine residue or cofactor that could be a sensor of an oxidative signal [unlike in the case of other oxidative stress-responsive transcriptional regulators such as OxyR, PerR, and SoxR (Storz & Imlay, 1999; Pomposiello & Demple, 2001; Lee & Helmann, 2006)], and it does not require any effector molecule for its transcriptional activation (Agari et al., 2008), there may be some unidentified factor(s) sensing oxidative stress and causing induced expression of SdrP. It has been demonstrated that the bacterial response to a specific stress can increase the resistance to other stresses, probably because stresses are not encountered in isolation in nature (Tesone et al., 1981; Jenkins et al., 1988; Jenkins et al., 1990; Hengge-Aronis et al., 1993; Storz & Imlay, 1999; Canovas et al.