Mineral-supported microbial functional differentiation across a vertical gradient in a vanadium-titanium magnetite mine.

Vanadium-titanium magnetite (VTM) mines are often associated with metal contamination, organic carbon depletion, and ecological degradation, yet how indigenous microbiomes respond to vertical geochemical heterogeneity remains poorly understood. Here, we investigated a ∼260 m vertical gradient in the Zhulan Iron Mine, China, by integrating elemental and mineralogical analyses with 16S rRNA gene amplicon and metagenomic profiling. Pronounced vertical stratification was observed. The lower-elevation section was enriched in vanadium (V) and Fe(II)-bearing minerals and harbored microbial communities with lower diversity but a more highly connected co-occurrence network. Representative lower-section taxa, including Thiobacillus, Sulfuricaulis, and Chloroflexota members, were linked to functional potentials for V-associated redox transformation, Fe/S metabolism, extracellular electron transfer, and autotrophic carbon fixation. These patterns suggest that Fe(II)-bearing minerals, particularly magnetite, may serve as potential inorganic electron sources supporting mineral-based lithotrophy and carbon fixation under metal-rich and organic-carbon-limited conditions. In contrast, the upper-elevation section exhibited lower V stress, higher microbial diversity, sparse vegetation, and enrichment of heterotrophic and plant- associated taxa, such as Sphingomonas, Flavisolibacter, and Actinomycetota, indicating a shift toward plant-supported microbial functions during early ecological recovery. Overall, this study links vertical geochemical stratification to microbial functional differentiation and highlights indigenous mineral-microbe interactions as a potential basis for targeted, low-input restoration strategies in metal-contaminated mining ecosystems.