Chemolithotrophic Biological Nitrogen Fixation Fueled by Antimonite Oxidation May Be Widespread in Sb-Contaminated Habitats

Abstract

Nitrogen (N) deficiency in mining-contaminated habitats usually hinders plant growth and thus hampers tailing revegetation. Biological N fixation (BNF) is an essential biogeochemical process that contributes to the initial accumulation of N in oligotrophic mining-contaminated regions. Previous studies reported that chemolithotrophic rather than heterotrophic diazotrophs frequently dominated in the mining-contaminated regions. Chemolithotrophic diazotrophs may utilize elements abundant in such habitats (e.g., sulfur (S), arsenic (As), and antimony (Sb)) as electron donors to fix N 2 . BNF fueled by the oxidation of S and As has been detected in previous studies. However, BNF fueled by Sb(III) oxidation (Sb-dependent BNF) has never been reported. The current study observed the presence of Sb-dependent BNF in slurries inoculated from Sb-contaminated habitats across the South China Sb belt, suggesting that Sb-dependent BNF may be widespread in this region. DNA-stable isotope probing identified bacteria associated with Rhodocyclaceae and Rhizobiaceae as putative microorganisms responsible for Sb-dependent BNF. Furthermore, metagenomicbinning demonstrated that Rhodocyclaceae and Rhizobiaceae contained essential genes involved in Sb(III) oxidation, N 2 fixation, and carbon fixation, suggesting their genetic potential for Sb-dependent BNF. In addition, meta-analysis indicated that these bacteria are widespread among Sb-contaminated habitats with different niche preferences: Rhodocyclaceae was enriched in river sediments and tailings, while Rhizobiaceae was enriched only in soils. This study may broaden our fundamental understanding of N fixation in Sbmining regions.

Differential Mechanisms of Microbial As(III) and Sb(III) Oxidation and Their Contribution to Tailings Reclamation

“…Accordingly, a cytoplasmic Sb(III) oxidase Ano, originally identified in Agrobacterium tumefaciens ( A. tumefaciens ) GW4, has been demonstrated to oxidize Sb (III) to Sb (V). , Further, the theoretical calculation of Gibbs free energy suggested different energy productions during As(III) and Sb(III) oxidation. The equations of As(III) or Sb(III) oxidation can be described as follows, with the Δ G f0 for AsO 2 – , AsO 4 3– , Sb(OH) 3 , and Sb(OH) 6 – being −350, −648, −647, and −1208 kJ/mol, respectively. − AsO 2 − + O 2 = AsO 4 3 − ; 0.25em normalΔ G 0 = prefix− 298 0.25em kJ / mol Sb false( OH ) 3 + 3 H + + 3 / 2 O 2 = Sb false( OH false) 6 − ; 0.25em normalΔ G 0 = prefix− 561 0.25em kJ / mol …”

“…In fact, As(III) and Sb(III) oxidation have both been suggested as important energy sources for nitrogen fixation identified in previous studies. 10,30,41−43 Although the functional population, including Serratia, Rhodocyclaceae, and Rhizobiaceae, that mediated these processes have been proposed, 30,43 the relative preference of As(III) and Sb(III) oxidation to fuel nitrogen fixation have not been investigated. Phosphate solubilization empowered by As(III) and Sb(III) oxidizers, on the other hand, has been less investigated.…”

“…The indigenous microbial communities contribute to primary succession of tailing sites via nutrient accumulation and facilitation of plant establishment. − Nutrient limitation, especially bioavailable nitrogen and phosphate, is a major factor that limits the reclamation of tailings. − Given their prevalence in mine tailings, ,, the As­(III) and Sb­(III) oxidizers could be critical for providing these essential services during tailing reclamation. In fact, As­(III) and Sb­(III) oxidation have both been suggested as important energy sources for nitrogen fixation identified in previous studies. ,,− Although the functional population, including Serratia , Rhodocyclaceae , and Rhizobiaceae , that mediated these processes have been proposed, , the relative preference of As­(III) and Sb­(III) oxidation to fuel nitrogen fixation have not been investigated. Phosphate solubilization empowered by As­(III) and Sb­(III) oxidizers, on the other hand, has been less investigated.…”

Widespread Distribution of the arsO Gene Confers Bacterial Resistance to Environmental Antimony

“…25−27 Generation of energy from Sb(III) oxidation may be coupled to nitrogen fixation. 28 Sb(III) oxidation has been proposed to be a microbial detoxification process that has the potential for Sb remediation. 29 To date, several Sb(III) oxidases have been identified and characterized.…”

“…Microbes are the key drivers for Sb redox transformations, catalyzing both Sb­(III) oxidation and Sb­(V) reduction. − Many bacteria mediate Sb­(III) oxidation, either for detoxification or for energy generation. − Generation of energy from Sb­(III) oxidation may be coupled to nitrogen fixation . Sb­(III) oxidation has been proposed to be a microbial detoxification process that has the potential for Sb remediation .…”