The MarR family regulator OsbR controls oxidative stress response, anaerobic nitrate respiration, and biofilm formation in Chromobacterium violaceum

• Published in: BMC microbiology Vol. 21; no. 1; p. 304
• Main Authors: Alves, Júlia A, Previato-Mello, Maristela, Barroso, Kelly C M, Koide, Tie, da Silva Neto, José F
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 04-11-2021; BioMed Central; BMC
• Subjects: Adhesins; Anaerobic conditions; Anaerobic respiration; Anaerobiosis; Antibiotics; Antioxidants; Bacteria; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biofilm formation; Biofilms; Cellular stress response; Chromobacterium - genetics; Chromobacterium - growth & development; Chromobacterium - metabolism; Chromobacterium violaceum; Deoxyribonucleic acid; DNA; DNA chips; DNA fingerprinting; DNA microarrays; Drug resistance; Enzymes; Gene clusters; Gene Expression Regulation, Bacterial; Gene regulation; Genes; Genetic aspects; Genomes; Gram-negative bacteria; Gram-positive bacteria; MarR family regulator; Metabolic pathways; Metabolism; Metabolites; Microbial mats; Nitrate reduction; Nitrates - metabolism; Nitrites - metabolism; Opportunist infection; Organic hydroperoxide; OsbR regulon; Oxidants; Oxidative Stress; Oxidizing agents; Phenotypes; Physiological aspects; Proteins; Reduction; Respiration; Transcription; Transcription factors; Transcription Factors - genetics; Transcription Factors - metabolism; Transcriptome analysis; Transcriptomes; Tuberculosis; Virulence; Brazil; OsbR regulon; Chromobacterium violaceum; Oxidative stress; Transcriptome analysis; Biofilm formation; MarR family regulator; Nitrate respiration
• ISSN: 1471-2180; 1471-2180
• DOI: 10.1186/s12866-021-02369-x

Chromobacterium violaceum is an environmental opportunistic pathogen that causes rare but deadly infections in humans. The transcriptional regulators that C. violaceum uses to sense and respond to environmental cues remain largely unknown.
Here, we described a novel transcriptional regulator in C. violaceum belonging to the MarR family that we named OsbR (oxidative stress response and biofilm formation regulator). Transcriptome profiling by DNA microarray using strains with deletion or overexpression of osbR showed that OsbR exerts a global regulatory role in C. violaceum, regulating genes involved in oxidative stress response, nitrate reduction, biofilm formation, and several metabolic pathways. EMSA assays showed that OsbR binds to the promoter regions of several OsbR-regulated genes, and the in vitro DNA binding activity was inhibited by oxidants. We demonstrated that the overexpression of osbR caused activation of ohrA even in the presence of the repressor OhrR, which resulted in improved growth under organic hydroperoxide treatment, as seem by growth curve assays. We showed that the proper regulation of the nar genes by OsbR ensures optimal growth of C. violaceum under anaerobic conditions by tuning the reduction of nitrate to nitrite. Finally, the osbR overexpressing strain showed a reduction in biofilm formation, and this phenotype correlated with the OsbR-mediated repression of two gene clusters encoding putative adhesins.
Together, our data indicated that OsbR is a MarR-type regulator that controls the expression of a large number of genes in C. violaceum, thereby contributing to oxidative stress defense (ohrA/ohrR), anaerobic respiration (narK1K2 and narGHJI), and biofilm formation (putative RTX adhesins).