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Redefining the Clostridioides difficile σB regulon: σB activates genes involved in detoxifying radicals that can result from the exposure to antimicrobials and hydrogen peroxide

ABSTRACT: In Gram-positive organisms the general stress response is regulated by the alternative sigma factor sigma B (σB). In C. difficile this sigma factor has been implicated in protection against stressors such as reactive oxygen species and antimicrobial compounds. Here, we show that an anti-σB antibody can be used to demonstrate overexpression of σB in C. difficile and that this overexpression is tolerated for short periods of time, despite its toxicity. Toxicity associated with σB-overexpression leads to loss of the plasmid used for anhydrotetracycline-induced σB expression. By uncoupling σB from its native regulatory network, we refined the previously proposed σB regulon and confirmed a direct role for σB in the induction of selected genes using in vitro run-off transcription reactions. Finally, using a plate-based luciferase reporter assay we demonstrated that different antibiotics and hydrogen peroxide induce genes positively regulated by σB in a manner dependent on this sigma factor. Together, our work suggests that lethal exposure to antibiotics may result in the formation of toxic radicals that lead to σB-dependent gene activation.

ORGANISM(S): Clostridioides difficile 630

PROVIDER: GSE152515 | GEO | 2020/09/07

REPOSITORIES: GEO

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Project description:In several gram-positive bacterial genera including Bacillus, Staphylococcus, and Listeria, sigma B (σB) has been identified as a stress-responsive alternative sigma factor responsible for initiating transcription of genes (the σB regulon) involved in response to stress-inducing environmental conditions. In L. monocytogenes, a foodborne pathogen of considerable threat to public health and the food industry, σB is involved in regulation of stress response and virulence gene expression. We have defined the σB regulon in L. monocytogenes during early stationary phase and under salt stress (0.3M NaCl) conditions using whole-genome microarrays, identifying 168 genes that generated ≥2.0-fold higher signals in the parental strain 10403S than in an isogenic sigB null mutant (ΔsigB), categorized into nine functional groups including stress-response genes (12), virulence genes (5), and genes related to transport (26) and metabolism (45). To gain a broader biological perspective of the σB stress response system, we applied these microarrays to Listeria innocua under the same environmental conditions. Our studies revealed 64 candidates in the L. innocua σB regulon with ≥2.0-fold higher signals in the parent than in a ΔsigB mutant; 49 of the 64 genes overlap with the L. monocytogenes σB regulon, indicating extensive overlap in σB-controlled genes between the two species. Further transcriptional analysis using TaqMan quantitative real time RT-PCR was performed for selected genes that displayed contrasting fold changes among the four microarray data sets (two stress conditions per species). We report novel members of the L. monocytogenes σB regulon, as well as the initial definition of the L. innocua σB regulon. Our comparative studies of the σB stress response systems in L. monocytogenes and L. innocua revealed features of the σB regulon that are conserved and unique to the two species. Keywords: Listeria monocytogenes, Listeria innocua, SigB regulon, salt stress, stationary phase

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Redefining the Clostridioides difficile σB regulon: σB activates genes involved in detoxifying radicals that can result from the exposure to antimicrobials and hydrogen peroxide

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