Nitrate-dependent antimony oxidase in an uncultured Symbiobacteriaceae member

Autotrophic antimony (Sb) oxidation coupled to nitrate reduction plays an important role in the transformation and detoxification of Sb. However, the specific oxidase involved in this process has yet to be identified. Herein, we enriched the microbiota capable of nitrate-dependent Sb(III) oxidation and identified a new Sb(III) oxidase in an uncultured member of Symbiobacteriaceae. Incubation experiments demonstrated that nitrate-dependent Sb(III) oxidation occurred in the microcosm supplemented with Sb(III) and nitrate. Both the 16S rRNA gene and metagenomic analyses indicated that a species within Symbiobacteriaceae played a crucial role in this process. Furthermore, carbon-13 isotope labelling with carbon dioxide-fixing Rhodopseudomonas palustris in combination with nanoscale secondary ion mass spectrometry revealed that a newly characterized oxidase from the dimethylsulfoxide reductase family, designated as NaoABC, was responsible for autotrophic Sb(III) oxidation coupled with nitrate reduction. The NaoABC complex functions in conjunction with the nitrate reductase NarGHI, forming a redox loop that transfers electrons from Sb(III) to nitrate, thereby generating the energy necessary for autotrophic growth. This research offers new insights into the understanding of how microbes link Sb and nitrogen biogeochemical cycles in the environment.