On the other hand, no significant increase in CC3252 expression was found in sigF mutant cells following dichromate exposure (Figure 1). Taken together, these results confirm the involvement of σF in C. crescentus response to chromium and cadmium stresses and suggest that the operon sigF-CC3252 is not

strongly auto-regulated under these conditions. To simplify our analyses and data presentation, we only show the expression of sigF and its target genes under dichromate stress in all subsequent experiments. Figure 1 Expression analysis of CC3255 and CC3252 under heavy metal stress. qRT-PCR experiments were performed with total RNA extracted from exponentially Proteases inhibitor growing cells immediately before and following exposure during 30 min to 55 μM potassium dichromate (K2Cr2O7), 55 μM cadmium chloride (CdCl2), 100 μM hydrogen peroxide (H2O2), 50 μM tert-butyl hydroperoxide (tBOOH), 100 μM paraquat or 50 μM diamide. Values represent the fold change in expression of CC3255 and CC3252 genes in parental strain NA1000 BAY 80-6946 manufacturer (WT) or the sigF mutant strain SG16 (ΔsigF), exposed or not to stress conditions, compared to the parental strain not exposed to stress. Results were normalized using gene CC0088 as the endogenous control, which was constitutively

expressed under the conditions analyzed. Data are mean values of two independent experiments; bars represent the standard error. Statistical analysis is shown in Additional file 1: Table S4. It is assumed that heavy metal ions cause oxidative stress inside cells [1, 12, 17]. This raises the possibility that

induction of σF-dependent genes by chromium and cadmium is a direct consequence of oxidative stress. To test this hypothesis, we stressed the parental and the sigF mutant strains with hydrogen peroxide, t-butyl hydroperoxide, paraquat (source of superoxide anion) or diamide (causes depletion of thiols). According to qRT-PCR PRKACG experiments, expression levels of CC3255 and CC3252 were not increased more than twofold in the parental strain during these stress conditions (Figure 1). In agreement, transcript levels of CC3255 and CC3252 were also not influenced by any of these stressors in cells lacking sigF. Concentrations of hydrogen peroxide and t-butyl hydroperoxide used in our analyses were previously found to be sufficient to increase expression of other genes in C. crescentus[15, 18]. Taken together, these data suggest that chromium and cadmium are able to induce the σF regulon in an oxidative stress independent manner. σF controls a small set of genes under chromium stress With the aim of identifying additional genes induced during stress conditions under the control of σF, we compared the gene expression pattern of parental cells with that of a sigF mutant under dichromate stress, using microarray chips containing up to three different probes corresponding to the beginning of the coding region of each gene from C. crescentus.