Role of organic acid-degrading bacteria in a microbial methanation system using a subterranean microbial community.

Abstract

Microbial methanation, which produces CH₄ from H₂ and CO₂ (H₂/CO₂) using hydrogenotrophic methanogens, converts CO₂ into a resource. The proposed system utilizes an isolated strain of hydrogenotrophic methanogen and an anaerobic microbial community from a deep aquifer where H₂ and CO₂ are produced via biodegradation of organic matter by fermentative bacteria, which CH₄ is then produced from H₂ and CO₂ by hydrogenotrophic methanogens. The strain and microbial community were added separately to liquid medium in serum bottles. An H₂/CO₂ mixture was added to each bottle's gas phase and incubated. CH₄ was produced continuously across both cultures. However, CH₄ production rates in the bottle with a single methanogen strain gradually decreased during cultivation with H₂ and CO₂ exchange. In contrast, the culture using the microbial community derived from anaerobic groundwater maintained consistent CH₄ production throughout the experiment. Analysis of organic acids in the media revealed that the accumulation of formate, acetate, and propionate in the microbial community culture was significantly lower than in the single-strain methanogen culture. These findings suggest that anaerobic bacteria efficiently decompose and consume organic acids that inhibit methanogenic activity, improving the culture environment. This study demonstrates the microbial community's effectiveness in supporting and sustaining a microbial methanation system.