Bacillus sp. SXB and Pantoea sp. IMH, aerobic As(V)-reducing bacteria isolated from arsenic-contaminated soil.

Aims To isolate highly effective aerobic As(V)-reducing bacteria from arsenic(As)-contaminated soils in Northwest China and to identify their dynamic As(V) reduction processes and genomic detoxification mechanisms. Methods and Results Enrichment cultures were performed aerobically in tryptone, yeast extract and glucose medium in the presence of As(V). Strain SXB isolated from soil in Shanxi Province, belonging to Bacillus genus, reduced As(V) more effectively under aerobic conditions than under anaerobic conditions. Strain IMH, a strictly aerobic isolate obtained from soil in Inner Mongolia, identified as Pantoea, is reported for the first time to reduce As(V). Both isolates could reduce over 90% As(V) in 36h under aerobic conditions. Putative gene fragments for the ArsB efflux pump gene were obtained from both strains. The putative arsenate reductase gene was only amplified from strain SXB. A putative arsH gene was amplified from strain IMH. Conclusions Strains SXB and IMH isolated from the As-contaminated soils reduce As(V) effectively under aerobic conditions via a detoxification mechanism regulated by ars operons. Significance and Impact of the Study Pantoea genus is reported to reduce As(V) for the first time. This study provides a full understanding of the highly effective As(V)-reducing bacteria SXB and IMH, which could influence the As biogeochemical cycle in soils.