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 (i) to understand the effects of CO, CO2, and H2 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 (PCO). Phylotypes of Methanobacteriaceae and methane production were detected at PCO ≤ 44.1 kPa. At higher PCO, 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.

Impact of carbon monoxide partial pressures on methanogenesis and medium chain fatty acids production during ethanol fermentation

“…Previous work (Alves et al, ; Guiot et al, ; Luo et al, ) reported that methanogens thrive at low P CO , mainly benefiting from acetate, H 2 , and CO 2 produced from CO, but that they are completely inhibited by the time CO reaches P CO ∼0.3 atm. Higher P CO was required to inhibit methanogens in granular sludge (Sipma et al, ), or after an acclimation period (Esquivel‐Elizondo, Delgado, & Krajmalnik‐Brown, ; Navarro et al, ).…”

“…Other potential carboxidotrophs detected in these experiments were Pleomorphomonas , Blautia , and Oscillospira . Phylotypes most closely associated to Pleomorphomonas , a hydrogenogenic carboxidotroph (Esquivel‐Elizondo, Delgado, & Krajmalnik‐Brown, ) were only detected (up to 3.3%) after the second addition of ethanol (second phase of fermentation) at P CO of 0.08–0.2 atm. This suggests that Pleomorphomonas might have been involved in the fatty acid elongation process, through generation of H 2 :CO 2 , but was inhibited at P CO = 0.3 atm.…”

“…In addition, phylotypes most closely related to Oscillospira were only abundant (2.5–9.2%) at P CO of 0.11–0.3 atm. Oscillospira phylotypes were detected (∼5%) in a mesophilic CO‐consuming culture enriched with CO (Esquivel‐Elizondo, Delgado, & Krajmalnik‐Brown, ).…”

“…Gas samples were analyzed for CO, H 2 , CO 2 , and CH 4 concentrations using gas chromatography as previously described (Esquivel‐Elizondo, Delgado, & Krajmalnik‐Brown, ). P CO was determined using Dalton's Law of partial pressures: P CO = % gas in headspace (estimated through gas chromatography) × total pressure in the serum bottle (measured with an electronic gauge manometer; VWR International, Radnor, PA).…”

“…A few studies on this topic have reported enhancement of acetogenesis and inhibition of methanogenesis at CO partial pressures ( P CO ) ≤ 0.3 atm (Alves et al, ; Guiot et al, ; Luo et al, ). Contrary to methanogens, several fermenters within the order Clostridiales have shown no inhibition by CO (Esquivel‐Elizondo, Delgado, & Krajmalnik‐Brown, ; Hussain et al, ; Luo et al, ).…”