Chemolithoautotrophic Antimonite Oxidation Coupled Nitrogen Fixation in the Rhizosphere of Local Plant in Antimony Tailing Area

Abstract

Antimony (Sb) tailings pose a significant environmental challenge. N-fixing microorganisms are essential for nutrient accumulation and plant colonization in degraded habitats. However, the oligotrophic conditions of tailings often inhibit the energy-intensive N-fixing process. This study identified a chemolithoautotrophic Sb(III) oxidation-coupled nitrogen fixation (SbNF) pathway in the rhizosphere of local plants. SbNF integrates biological detoxification and nutrient accumulation, enabling plant colonization and ecological restoration of degraded habitats. Multi-omic analyses reveal that Sb content strongly shapes the composition of Sb-oxidizing and N-fixing bacterial communities in the rhizosphere. Abundant marker genes for carbon fixation (cbbL), Sb(III) oxidase (aioAB/anoA), and nitrogenase (nifH) were consistently detected in SbNF metagenome-assembled genomes. Positive correlations between gene abundances associated with autotrophic potential (aioA-cbbL) and coupling potential (aioA-nifH) were observed in the rhizoplane but not in the endosphere. In addition to genetic potentials, high-throughput cultivation of native SbNF-isolates (e.g., Pseudomonas, Arthrobacter, and Sphingomonas) confirmed their rapid Sb(III) oxidation coupling autotrophic growth and nitrogen fixation. Isolates also exhibited plant growth-promoting traits, including indole-3-acetic acid production, phosphate solubilization, and siderophore secretion, providing multiple benefits to host plants. Co-cultivation of these isolates revealed minimal antagonism, suggesting the potential for designing synthetic microbial communities for sustainable phytoremediation. Cross-validation further suggests that SbNF is widespread in the rhizosphere of various local plants. These findings uncover a novel biogeochemical process in the rhizosphere, linking mineral oxidation, autotrophic growth, and nitrogen fixation, highlighting its importance for the ecological restoration of degraded tailing area.