Evolution of microbial communities growing with carbon monoxide, hydrogen and carbon dioxide

Abstract

Microbial anaerobic conversion of carbon monoxide (CO) and syngas (mainly composed of CO, CO₂ and H₂) leads to the production of important industrial products, such as acetate and ethanol. The composition of CO- and syngas-converting microbial communities, and the microbial interactions involved are still largely unknown. The main objectives of this study were 1) to understand the effects of CO, CO₂ and H₂ on the structure and function of a CO-consuming microbial community, and 2) to identify key carboxidotrophs in the mixed culture. For this, sludge was anaerobically enriched with CO as the sole carbon/energy source at incrementally increasing CO partial pressures (P_CO). Phylotypes of Methanobacteriaceae and methane production were detected at P_CO ≤ 44.1 kPa. At higher P_CO, enriched phylotypes were Acetobacterium, Oscillospira, and Pleomorphomonas, and acetate was the main end-product. The addition of CO₂/HCO₃⁻ or H₂ to CO-fermentation increased the acetate/ethanol ratio and species diversity, compared to growth with CO as sole substrate. Phylotypes associated with Pleomorphomonas and Acetobacterium increased in relative abundance during exponential CO-utilization. The Pleomorphomonas-like isolate produced H₂:CO₂, whereas the Acetobacterium-like isolate produced ethanol, when CO was the only electron/carbon source. These findings shed light on the interplay between syngas components and microbial communities.

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