Challenging the paradigm of metabolic exclusivity: coexistence of methanogenesis and sulfate reduction in oil reservoirs

The prevailing dogma in microbial ecology holds that sulfate-reducing microorganisms (SRMs) outcompete methanogenic archaea for common substrates (e.g., H2/formate and acetate), leading to the mutual exclusion of sulfate reduction and methanogenesis in sulfate-rich anaerobic environments. This principle underpins models of organic carbon flow to sulfate-respiration-derived CO2 in ecosystems like oil reservoirs, where seawater injection introduces high concentrations of sulfate. In an Applied and Environmental Microbiology article by S. Beilig, L. Voskuhl, I. Geydirici, L. K. Tintrop, T. C. Schmidt, and R. U. Meckenstock (91:e00141-25, 2025, https://doi.org/10.1128/aem.00141-25), the authors challenge this view by demonstrating coexistence of methanogenesis and sulfate reduction in a sulfate-adapted enrichment culture from an oil reservoir. The authors employ incubation experiments and microbial activity assessment via the reverse stable isotope labeling (RSIL) method to argue for metabolic coexistence, even under conditions thought to favor complete competitive exclusion. This commentary discusses the mechanistic reasons underlying the coexistence and explores the broader implications for predicting microbial activities and interactions. The study compellingly argues that thermodynamic and kinetic arguments alone are insufficient to predict microbial community function, necessitating a more nuanced understanding of microbial interactions in complex environments.