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

Microbial anaerobic conversion of carbon monoxide (CO) and syngas (mainly composed of CO, CO2 and H-2) 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 (i) to understand the effects of CO, CO2, and H-2 on the structure and function of a CO-consuming microbial community, and (ii) 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 H-2 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 H-2: 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.