ABSTRACT
Recent studies demonstrated that microbial arsenite (As(III)) oxidation associated with nitrate (NO3 −) reduction might be an important process in diminishing arsenic bioavailability and toxicity to rice when paddy soils are contaminated by arsenic. However, the responses of bacterial communities and functional genes to As(III) under nitrate-reducing conditions are poorly understood in a non-contaminated soil. Our results revealed that microbial oxidation of As(III) to As(V) was substantially accelerated by nitrate addition in a paddy soil with low arsenic background content, while nitrate reduction was not affected by As(III) addition. Metagenomic binning revealed that Pseudogulbenkiania sp. was the main nitrate-reducing bacteria with narG, nirS and norBC genes, and Azoarcus sp. was the predominant As(III)-oxidizing bacteria with As(III) oxidase genes aioA and aioB. It was also confirmed that the abundance of Azoarcus spp. and aioA genes were enhanced in the presence of As(III) and nitrate. These findings suggest that non-contaminated paddy soils also harbor arsenic oxidizing bacteria and genes, which could be stimulated in the presence of As(III) and nitrate.
