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

Jingxin Li,Gejiao Wang,Yuxiao Zhang,Shiling Zheng,Fanghua Liu

doi:10.3389/fmicb.2019.00360

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.

Highlights

Antimony (Sb) is a metalloid that is widely used in a variety of industrial products and medical treatments (Filella et al, 2002a; Vásquez et al, 2006; Wilson et al, 2010; He et al, 2012; Li et al, 2016)
In addition to the chemical Sb(III) oxidants (e.g., H2O2, iodate, and frequently co-occurs with iron (Fe) and Mn oxyhydroxides) (Belzile et al, 2001; Leuz and Johnsona, 2005; Quentel et al, 2006), microorganisms play an important role in Sb(III) oxidation, and this oxidation reaction serves as detoxification process for the microorganisms (Li et al, 2016)
It has been reported that the multicopper oxidase may play a role in bacterial anaerobic Fe(II) oxidation (He et al, 2016)

Summary

Introduction

Antimony (Sb) is a metalloid that is widely used in a variety of industrial products (e.g., flame retardants, small arms ammunition, semiconductors and batteries) and medical treatments (e.g., for leishmaniasis) (Filella et al, 2002a; Vásquez et al, 2006; Wilson et al, 2010; He et al, 2012; Li et al, 2016). Sb mainly exists in two oxidation states, antimonite [Sb(III)] and antimonate [Sb(V)]. In aqueous environments at a neutral pH, Sb(III) is more prevalent in anoxic environments [as Sb(OH)3], and Sb(V) is dominate under oxic conditions [as Sb(OH)6] (Filella et al, 2002b; Hockmann et al, 2014). Sb(III) compounds are much more toxic than those containing Sb(V); Sb(III) oxidation, which transforms the toxic Sb(III) to the less toxic Sb(V), has a significant value for bioremediation of Sbcontaminated environments

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