The first experiment compared PS5 and NorE5 expression levels and showed that not only was a band of the expected size detected but also its expression was significantly increased in NorE5 (Fig. 2). The second experiment compared

strains GC4468 and JTG936 and showed a similarly increased expression in the SoxS-overexpressing strain JTG936 (Fig. 2). click here Thus, we conclude from these experiments that the ydbK and the ompN genes are cotranscribed. To further test whether SoxS induced the cotranscription of ydbK and ompN, a ydbK::lacZ fusion was constructed (strain M4458b; Fig. 1). This transcriptional fusion was activated 19-fold by treatment with PQ. A moderate effect was found for DIP treatment Selleckchem SCH727965 (3.5-fold), but no significant activation was found for SAL (1.2-fold; Table 3). Moreover, to rule out any possible side effect of PQ treatment, strain M4458b was transformed with the plasmids pRGM9817, pJLR70, pRGM9818, pRGM489, and pRGM5009, which respectively correspond to the vector alone or carrying SoxS, MarA, Rob, and MarA E89A (a modified MarA protein with the substitution E89A which has been shown to act like SoxS in the preferential activation of the regulon genes (Martin & Rosner, 2011). Accordingly, the

results shown in Table 3 indicate that only SoxS or MarA E89A can activate the ydbK promoter (10- and 5-fold increments, respectively). As has been previously reported, all genes belonging to the SoxS regulon contain a 20 bp motif, termed soxbox, in their promoter where the regulator binds to activate their expression (Martin & Rosner, 2002; Fabrega et al., 2010). By Casein kinase 1 means of bioinformatic tools we tried to find a DNA fragment matching the consensus soxbox sequence but we could not identify such a motif, suggesting that the SoxS effect observed on the ydbK promoter could be indirect, that is, acting via an unknown regulator. Similarly, recent results have reported an indirect effect for SoxS (not MarA or Rob) in activating the znuACB genes involved in zinc uptake and growth in the absence or limitation of zinc (Warner & Levy, 2012). Mutants of the ompN and ydbK

genes were constructed in the wild-type background of GC4468 (strains M6131 and M6133, respectively) and in the multipump mutant strain M5950 (strains M6135 and M6137, respectively). As the YdbK function has been related to superoxide resistance and this two-gene operon is activated by SoxS and not by MarA, the mutants were tested for resistance to oxidative stress. These mutants were grown in LB and M9 agar plates in the absence and presence of several concentrations of the superoxide-generating agent PQ (10, 20, 30, and 40 μg mL−1). Results showed that only the ydbK mutant displayed a significant growth restriction phenotype when grown on M9 plates with a PQ concentration equal and higher than 30 μg mL−1 [similar to previous results (Eremina et al., 2010)].