However, the signal transduction and control processes involved in the bacterial response to these heavy

metals are still poorly characterized. The C. crescentus genome encodes 13 extracytoplasmic function (ECF) sigma factors [13]. Two of them, the paralogous σT and σU, are involved in the response to various environmental stress conditions, including chromium and cadmium stresses [12, 14]. Additionally, σE mediates a rapid transcriptional Syk inhibitor response to cadmium, organic hydroperoxide, singlet oxygen and UV-A [15]. In a previous report, σF was found to be required for bacterial survival under hydrogen peroxide stress in the stationary growth phase, but no σF-mediated transcriptional response to hydrogen peroxide could be observed [16]. Thus, the involvement of σF in a transcriptional response to environmental stresses still

needs to be characterized. The observation that Evofosfamide concentration genes CC2906, CC3255 and CC3257, previously found to be dependent on σF[16], are induced following C. crescentus exposure to chromate, dichromate and cadmium [12] suggested to us that σF could be involved in the transcriptional response to these heavy metals. In the present work, we demonstrate the involvement of σF in chromium and cadmium stress responses. We also identified

many the set of genes regulated by σF by using global transcriptome analysis and characterized the AMN-107 promoter region of these genes by 5´RACE experiments and β-galactosidase assays. Furthermore, we investigated the role of the protein encoded by the second gene in the sigF operon (CC3252), here named NrsF, and two conserved cysteine residues in this protein on the σF-mediated response to heavy metals. Results σF is involved in chromium and cadmium responses in C. crescentus In order to verify a possible involvement of σF in the C. crescentus response to chromium and cadmium stresses, we monitored expression of CC3255, previously identified as a σF-dependent gene, as well as CC3252, which is co-transcribed with sigF (CC3253), by quantitative RT-PCR. This analysis showed that CC3255 is significantly induced in parental cells following exposure to either dichromate or cadmium (Figure 1). In contrast, expression of CC3255 in a sigF deletion mutant strain exposed to dichromate or cadmium was found to be quite similar to that observed in the same strain under no stress condition (Figure 1).