A new type of ArsR transcriptional repressor controls transcription of the arsenic resistance operon of <i>Arsenicibacter rosenii</i> SM‐1

Impact statement Arsenic is the most common toxic metalloid in the environment. Nearly all organisms have genes for arsenic detoxification. Arsenic detoxification genes are frequently organized in chromosomal or plasmid‐encoded arsenic resistance ( ars ) operons, which are commonly regulated by members of the ArsR transcriptional repressors. To date, three As(III)‐responsive ArsRs with different As(III) binding sites have been identified. Here, we identify a new type of As(III)‐responsive ArsR repressor that has an atypical As(III) binding site and controls transcription of the ars operon of Arsenicibacter rosenii SM‐1. Our results provide new insights into the classification and evolution relationship of the ArsR transcriptional repressors.