Identification of anaerobic arsenite‐oxidizing and arsenate‐reducing bacteria associated with an alkaline saline lake in Khovsgol, Mongolia

Summary Microbial arsenic transformation pathways associated with a saline lake located in northern M ongolia were examined using molecular biological and culturing approaches. Bacterial 16 S rRNA gene sequences recovered from saline lake sediments and soils were affiliated with haloalkaliphiles, including B acillus and H alomonas spp. Diverse sequences of arsenate respiratory reductase ( arrA ) and a new group of arsenite oxidase ( arxA ) genes were also identified. Pure cultures of arsenate‐reducing N itrincola strain and anaerobic arsenite‐oxidizing H alomonas strain were isolated. The chemoorganotrophic H alomonas strain contains arxA gene similar to that of a chemoautotrophic arsenite‐oxidizing A lkalilimnicola ehrlichii strain MLHE ‐1. These results revealed the diversity of arsenic transformation pathways associated with a geographically distinct saline system and the potential contribution of arx ‐dependent arsenite oxidation by heterotrophic bacteria.