Harnessing high-level hydrogen sulfide stress for enhanced biogas utilization: Adaptive resilience of a mixed-culture system

Biogas, a mixture predominantly composed of methane (CH₄) and carbon dioxide (CO₂), serves as a substrate for diverse microorganisms, including methanotrophs and microalgae, facilitating carbon sequestration, mitigating greenhouse gas emissions, and generating biomass for multifarious applications. However, the presence of hydrogen sulfide (H₂S), a common contaminant in biogas, can exert toxic effects on these microorganisms, potentially inhibiting their growth and metabolic processes. This study investigated the effects of H₂S on a mixed-culture system utilizing a long-term continuous flow photobioreactor. The results demonstrated that the mixed-culture system could tolerate H₂S concentration up to 1000 ppm without significant performance deterioration. Notably, when the mixed-culture system was exposed to a higher H₂S concentration (5000 ppm) for an extended period of one month, the CH₄ and CO₂ utilization rates increased threefold. Furthermore, the primary byproduct, protein, constituted over 50 % of the cell dry weight. Comprehensive analysis of the microbial community composition and metabolic pathways revealed adaptive shifts in response to H₂S stress. In-depth analysis of functional genes indicated that the system possessed the capacity to adapt and maintain its functionality even under severe H₂S stress. This study provides valuable insights into microbial and metabolic mechanisms underlying H₂S resistance in a mixed culture, providing an opportunity for the establishment of an H₂S-resistant biosystem for practical biogas transformation.