Consortium-level features and microbial mechanisms associated with enhanced sulfate reduction under microaerophilic...

Microaerophilic environments are widespread in sulfate-rich waste systems, yet the mechanisms enabling efficient sulfate reduction under microaerophilic rather than strictly anaerobic conditions remain poorly understood. Here, we compared eight enriched microbial consortia derived from coal gangue habitats to identify the physicochemical, structural, and microbial determinants of sulfate reduction performance. During 14-day incubation, sulfate reduction followed a clear three-phase kinetic pattern, and the consortia separated into high- and low-performance groups after day 6. High-performance consortia exhibited significantly greater biomass accumulation, faster establishment of reducing conditions, narrower pH fluctuations, lower electrical conductivity, smaller aggregate size, and zeta potentials closer to neutrality. X-ray photoelectron spectroscopy revealed the coexistence of SO₄^2 -, SO₃^2-, S₂O₃^2-, S₂^2-, and S^2-, indicating mixed sulfur redox signatures in the biogenic precipitates rather than a single terminal sulfide pool. Microbial community analyses showed that high sulfate-reduction performance was associated with lower alpha diversity, stronger network centralization, and dominance of Enterobacter and Klebsiella. Functionally, high-performance consortia were enriched in genes involved in sulfate uptake and activation and organosulfur transport, whereas low-performance consortia showed relatively stronger signals related to sulfur-containing amino acid biosynthesis. Sulfur intermediates were positively associated with sulfur transport/activation genes but negatively associated with biosynthetic genes, suggesting a potential linkage between mixed sulfur redox signatures and sulfur acquisition/activation processes. Overall, efficient sulfate reduction was associated with a consortium-level configuration characterized by biomass growth, rapid redox buffering, compact aggregate organization, and coordinated sulfur metabolic reallocation. These findings provide a mechanistic interpretation for engineering robust sulfate-reducing microbiomes in oxygen-fluctuating contaminated environments.