Functional Microbial Communities Involved in As(III) Oxidation Coupled with Nitrate Reduction in a Paddy Soil

Arsenite (As(III)) oxidation coupled with nitrate (NO3-) reduction is thermodynamically favored and experimentally tested. However, little is known about the functional bacteria responsible for this coupling process in flooded paddy soil. In this study, three microcosms containing paddy soil amended with 1) As(III) + NO3-, 2) As(III), and 3) NO3- were set up to investigate the coupled processes of As(III) oxidation and NO3- reduction and to characterize the associated functional bacteria. The results showed that As(III) was completely oxidized in the Soil + As(III) + NO3- treatment, while no As(III) oxidation was observed with As(III) amendment. NO3- reduction was observed in both the Soil + As(III) + NO3- and Soil + NO3- treatments, where nitrite (NO2-) was the major product. In the Soil + As(III) + NO3- treatment, the 16S rRNA-based dominant genera were Vogesella, Dechloromonas, and Pseudogulbenkiania; the aoxB-based dominant arsenite-oxidizers included Cupriavidus and Acidovorax; and the narG-based dominant nitrate reducers (NO3- & RARR; NO2-) were Dechloromonas and Pseudogulbenkiania. Comparison of the aoxB and narG gene markers at 90% similarity indicated a higher diversity of aoxB than narG gene markers based on & alpha;-diversity indices in the As(III) + NO3- treatment. In addition, although the dominant arsenite-oxidizing bacteria Cupriavidus and Acidovorax had a lower relative abundance in paddy soil, they played an important role in As(III) oxidation. The findings of this study provide a better understanding of the functional microbial communities involved in As(III) oxidation coupled with NO3- reduction in anoxic paddy soil.