Anaerobic Bacterial Immobilization and Removal of Toxic Sb(III) Coupled With Fe(II)/Sb(III) Oxidation and Denitrification

Abstract

Antimony (Sb) pollution is a worldwide problem. In some anoxic sites, such as Sb mine drainage and groundwater sediment, the Sb concentration is extremely elevated. Therefore, effective Sb remediation strategies are urgently needed. In contrast to microbial aerobic antimonite [Sb(III)] oxidation, the mechanism of microbial anaerobic Sb(III) oxidation and the effects of nitrate and Fe(II) on the fate of Sb remain unknown. In this study, we discovered the mechanism of anaerobic Sb(III) oxidation coupled with Fe(II) oxidation and denitrification in the facultative anaerobic Sb(III) oxidizer Sinorhizobium sp. GW3. We observed the following: (1) under anoxic conditions with nitrate as the electron acceptor, strain GW3 was able to oxidize both Fe(II) and Sb(III) during cultivation; (2) in the presence of Fe(II), nitrate and Sb(III), the anaerobic Sb(III) oxidation rate was remarkably enhanced, and Fe(III)-containing minerals were produced during Fe(II) and Sb(III) oxidation; (3) qRT-PCR, gene knock-out and complementation analyses indicated that the arsenite oxidase gene product AioA plays an important role in anaerobic Sb(III) oxidation, in contrast to aerobic Sb(III) oxidation; and (4) energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and powder X-ray diffraction (XRD) analyses revealed that the microbially produced Fe(III) minerals were an effective chemical oxidant responsible for abiotic anaerobic Sb(III) oxidation, and the generated Sb(V) was adsorbed or coprecipitated on the Fe(III) minerals. This process included biotic and abiotic factors, which efficiently immobilize and remove soluble Sb(III) under anoxic conditions. The findings revealed a significantly novel development for understanding the biogeochemical Sb cycle. Microbial Sb(III) and Fe(II) oxidation coupled with denitrification has great potential for bioremediation in anoxic Sb-contaminated environments.

Bacteria Responsible for Nitrate-dependent Antimonite Oxidation in Antimony-contaminated Paddy Soil Revealed by the Combination of DNA-SIP and Metagenomics

“…Genomic DNAs from the C-and 12 C-NaHCO 3 SIP incubations (day 0, 30 and 60) were separated into "heavy" (i.e., 13 C-DNA) and "light" (i.e., 12 C-DNA) fractions by isopycnic density gradient centrifugation as previous [34]. Brie y, approximately 2 µg of genomic DNA was added into CsCl solution (buoyant density (BD) = 1.714 g mL − 1 ) in an OptiSeal polyallomer tube (Beckman Coulter, Palo Alto, USA).…”

“…Genomic DNAs from the nitrate-dependent SbOB enrichment incubations (day 0, 12, 30 and 60) were subject to amplicon sequencing of the partial 16S rRNA gene with the primers 520f(5'-AYTGGGYDTAAAGNG-3')/802r(5'-TACNVGGGTATCTAATCC-3') [59]. In addition, three representative heavy or light fractions containing the highest aioA gene abundance from each culture of the 13 CSbN (H1-H3), 12 CSbN (L1-L3) and 13 CN (H1-H3) treatments (day 60) were pooled as composite DNA samples respectively, and then the nine composite DNA samples (one composite DNA sample per culture, triplicate cultures per treatment) were sequenced for the partial 16S rRNA gene with the primer set 520f/802r. The amplicon sequencing was performed on an Illumina MiSeq platform (Personalbio, Shanghai, China) [60].…”

“…Typically, two oxidation states of Sb, namely antimonite (Sb(III)) and antimonate (Sb(V)), are the main forms of Sb in nature [9,10]. The mobility, bioavailability and toxicity of Sb strongly depends on its oxidation state, for instance, Sb(V) is less toxic than Sb(III) [11][12][13].…”

“…NLS4 and Sinorhizobium sp. GW3) have been isolated using nitrate as the electron acceptor [13,18,27]. The anoxic conditions and high concentrations of nitrate caused by N fertilization would allow rice paddies to facilitate nitrate-dependent SbO.…”

“…It is proposed that the long-term Sb contaminated may enrich Sbmetabolising bacteria including nitrate-dependent SbOB and makes these Sb-contaminated rice paddy soils ideal for this study. Although three nitrate-dependent SbOB have been isolated and identi ed so far [13,18,27], their overall diversity and distribution in soil, especially in rice paddy soil, is not known. Culture-independent DNA-stable isotope probing (SIP) incubations can link microbial identity with function in environment and enable a greater understanding of active microbial communities involved in the process under study [30].…”