Project description:Here, we described a novel transcriptional regulator belonging to the MarR family that we named OsbR (oxidative stress response and biofilm formation regulator) in the opportunistic pathogen Chromobacterium violaceum. Transcriptome profiling by DNA microarray using strains with deletion or overexpression of osbR showed that OsbR exert 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. We showed that the proper regulation of the nar genes by OsbR ensures an optimal growth of C. violaceum under anaerobic conditions by tuning the reduction of nitrate to nitrite. Finally, the osbR overexpressing strain showed reduction in biofilm formation and this phenotype correlated with the OsbR-mediated repression of two gene clusters encoding putative adhesins.
Project description:Antibiotic resistance can arise by several mechanisms, including mutation in transcription factors that regulate drug efflux pumps. In this work, we identified EmrR as a MarR family transcription factor involved in antibiotic resistance in Chromobacterium violaceum, a Gram-negative bacterium that occurs in soil and water and can act as a human opportunistic pathogen. Antibiogram and minimum inhibitory concentration (MIC) assays showed that the ΔemrR mutant presented increased resistance to the antibiotic nalidixic acid in respect to the wild-type strain. The emrR gene is near to a putative operon emrCAB, which encode the efflux pump EmrCAB. DNA Microarray analysis showed that EmrR represses the emrCAB operon and some other putative transporters. Northern blot assays validated that EmrR represses the emrCAB operon and this repression can be released by salicylate, but not other compounds such as nalidixic acid or ethidium bromide. Electrophoretic mobility shift assays (EMSA) showed that EmrR binds directly to the promoter regions of emrR, emrCAB and other genes to exert negative regulation. Therefore, in response to compounds as salicylate, EmrR derepresses the operon emrCAB causing overexpression of the efflux pump EmrCAB and increased resistance to nalidixic acid in C. violaceum.
