Enrichment of anaerobic syngas‐converting bacteria from thermophilic bioreactor sludge

Thermophilic (55 °C) anaerobic microbial communities were enriched with a synthetic syngas mixture (composed of CO , H 2 , and CO 2 ) or with CO alone. Cultures T ‐ S yn and T ‐ CO were incubated and successively transferred with syngas (16 transfers) or CO (9 transfers), respectively, with increasing CO partial pressures from 0.09 to 0.88 bar. Culture T ‐Syn, after 4 successive transfers with syngas, was also incubated with CO and subsequently transferred (9 transfers) with solely this substrate – cultures T ‐ S yn‐ CO . Incubation with syngas and CO caused a rapid decrease in the microbial diversity of the anaerobic consortium. T ‐ S yn and T ‐ S yn‐ CO showed identical microbial composition and were dominated by D esulfotomaculum and C aloribacterium species. Incubation initiated with CO resulted in the enrichment of bacteria from the genera T hermincola and T hermoanaerobacter . Methane was detected in the first two to three transfers of T‐Syn, but production ceased afterward. Acetate was the main product formed by T ‐ S yn and T ‐ S yn‐ CO . Enriched T ‐ CO cultures showed a two‐phase conversion, in which H 2 was formed first and then converted to acetate. This research provides insight into how thermophilic anaerobic communities develop using syngas/ CO as sole energy and carbon source can be steered for specific end products and subsequent microbial synthesis of chemicals.