Highly active sulfate-reducing bacteria drive biogenic souring in oil reservoirs: insights from metabolic capability and microbial interactions

In reservoir microbiome, sulfate-reducing bacteria (SRB) dominate the biogeochemical cycling of sulfur elements. As the main biological source of hydrogen sulfide (H₂S) in oil reservoirs, SRB also cause substantial economic losses in oil reservoirs. Effective souring control requires a deeper understanding of SRB activity, especially the highly efficient H₂S-producing strains. However, current studies have largely emphasized community-level analysis, leaving the role of key SRB species and their interactions with other functional microorganisms poorly resolved. Firstly, integrated metagenomic and culture-based analyses of the original samples from Chengbei Oilfield revealed temperature as the key factor shaping SRB structure, and the highest H₂S production rates were observed under high-temperature conditions (60 °C). Within the SRB community, we proposed that highly active—rather than abundant—SRB were the primary drivers of biogenic H₂S production. Although Desulfofundulus and Desulfotomaculum represented only 3.13% and 6.41% of the community, respectively, their presence strongly correlated with H₂S accumulation ( p < 0.05). In contrast, the highly abundant Desulfovibrio (46.20%) showed no significant correlation. Further analysis using metabolic modeling revealed syntrophic interactions between SRB (including Desulfofundulus and Desulfotomaculum ) and hydrocarbon-degraders, highlighting microbial cooperation as an accelerator of souring. The subsequent isolation of Desulfofundulus sp. 13 T and Desulfotomaculum sp. 45–6 showed distinct metabolic strategies for sulfide production, governed by their inherent metabolic capacities and substrate preferences: Desulfofundulus sp. 13 T was regarded as the key species, which could degrade n -hexadecane (67.79% in 10 days) and crude oil, producing > 1000 ppm H₂S in 3 days, but less than in lactate medium (> 2000 ppm/24 h); Desulfotomaculum sp. 45–6 demonstrated limited alkane degradation and could produce < 1000 ppm H₂S only supplemented with methanol or lactate. Their respective roles and contribution to ecosystem functions, particularly H₂S production, is not equivalent. Our findings establish that metabolic activity, not relative abundance, is the key predictor of the environmental impact of SRB. This study provides a mechanistic understanding of reservoir souring by identifying metabolically dominant taxa and synergistic interactions within microbial communities, offering a trait-based framework for developing targeted souring management strategies. Video Abstract