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

Júlia A Alves,José F Da Silva Neto,Tie Koide,Kelly C M Barroso,Maristela Previato-Mello

doi:10.1186/s12866-021-02369-x

Júlia A Alves, José F Da Silva Neto + Show 3 more

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https://doi.org/10.1186/s12866-021-02369-x

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Abstract

BackgroundChromobacterium 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.ResultsHere, 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.ConclusionsTogether, 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).

Highlights

Chromobacterium violaceum is an environmental opportunistic pathogen that causes rare but deadly infections in humans
We have shown that OhrR affects C. violaceum virulence and is involved in resistance to organic hydroperoxides by regulating ohrA [30, 32], while EmrR confers antibiotic resistance by regulating the MFS-type efflux pump EmrCAB [31]
OsbR responds to oxidation and has an antioxidant role Considering that OsbR has two cysteine residues (Additional file 1, Fig. S1) and when overexpressed activates the genes ohrA/ohrR (Fig. 3, Fig. 4, Additional file 2, Table S2), which encode an organic hydroperoxide antioxidant system in C. violaceum [30, 32], we investigated whether OsbR dimerizes upon oxidation by

Summary

Introduction

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. Chromobacterium violaceum is a Gram-negative betaproteobacterium found in tropical and subtropical ecosystems around the world, primarily in water and soil samples [1, 2]. C. violaceum can cause rare but deadly opportunistic infections in humans and other animals, entering the hosts mainly through skin lesions. Similar to other environmental pathogens, C. violaceum has complex regulatory systems and versatile metabolic capacities to survive under several stress conditions [5,6,7]. The transcriptional regulators involved in C. violaceum adaptation to diverse environments remain poorly investigated

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