Characterization of arsenic-metabolizing bacteria in high arsenic-contaminated soil from Hetao Plain, Inner Mongolia

Arsenic (As) is a toxic metalloid and microbially-mediated As transformation are crucial for management of As contamination. Indigenous microbial communities involved in As transformation in the As-contaminated soils are largely unknown. Here we investigate two major pathways of As transformation, i.e., As(III) oxidization and As(V) reduction, and identify the As(III)-oxidizing and As(V)-reducing bacteria in the soil by combining stable isotope probing with shotgun metagenome. As(III) oxidization concomitant with significant increase of the aioA genes copies were observed in the treatments amended with As(III) and NO3-, whereas no obvious As(III) oxidization or increases of the aioA genes abundance were detected in the treatment amended with As(III) only. These results suggested that As(III) oxidization can couple with nitrate reduction and mainly catalysed by the microorganisms containing aioA gene. As(V) reduction was detected in the treatments amended with As(V) and acetate where the abundance of arrA gene significantly increased, indicating that microorganisms with arrA gene were the key drivers of As(V) reduction. Acidovorax, Hydrogenophaga, and Ramlibacter were the putative nitrate-dependent As(III) oxidizers, and Deinococcus and Serratia were the putative As(V) reducers. These findings will improve our understanding of As metabolism and are meaningful for mapping out bioremediation strategies of As contamination.