Identification of a MarR Subfamily That Regulates Arsenic Resistance Genes.

In this study, comprehensive analyses were performed to determine the function of an atypical MarR homolog in sp. strain As-55. Genomic analyses of sp. As-55 showed that this is located adjacent to an gene. ArsV is a flavin-dependent monooxygenase that confers resistance to the antibiotic methylarsenite [MAs(III)], the organoarsenic compound roxarsone(III) [Rox(III)], and the inorganic antimonite [Sb(III)]. Similar genes are widely distributed in arsenic-resistant bacteria. Phylogenetic analyses showed that these MarRs are found in operons predicted to be involved in resistance to inorganic and organic arsenic species, so the subfamily was named MarR. MarR orthologs have three conserved cysteine residues, which are Cys36, Cys37, and Cys157 in sp. As-55, mutation of which compromises the response to MAs(III)/Sb(III). GFP-fluorescent biosensor assays show that AdMarR (MarR protein of Achromobacter deleyi As-55) responds to trivalent As(III) and Sb(III) but not to pentavalent As(V) or Sb(V). The results of RT-qPCR assays show that is expressed constitutively in a deletion mutant, indicating that represses transcription of . Moreover, electrophoretic mobility shift assays (EMSAs) demonstrate that AdMarR binds to the promoters of both and in the absence of ligands and that DNA binding is relieved upon binding of As(III) and Sb(III). Our results demonstrate that AdMarR is a novel As(III)/Sb(III)-responsive transcriptional repressor that controls expression of which confers resistance to MAs(III), Rox(III), and Sb(III). AdMarR and its orthologs form a subfamily of MarR proteins that regulate genes conferring resistance to arsenic-containing antibiotics. In this study, a MarR family member, AdMarR was shown to regulate the gene, which confers resistance to arsenic-containing antibiotics. It is a founding member of a distinct subfamily that we refer to as MarR, regulating genes conferring resistance to arsenic and antimony antibiotic compounds. AdMarR was shown to be a repressor containing conserved cysteine residues that are required to bind As(III) and Sb(III), leading to a conformational change and subsequent derepression. Here we show that members of the MarR family are involved in regulating arsenic-containing compounds.