Acetate production from H2/CO2 by mixed cultures from diverse ecosystems and their application for syngas fermentation

Abstract:

[Objective] We studied acetate production from H2/CO2 by mixed cultures from diverse ecosystems and applied the system for syngas fermentation. [Methods] Undefined mixed cultures from waste activate sludge, freshwater sediment, anaerobic methanogenic sludge and cow manure were used for the bioconversion of H2/CO2 and enriched H2/CO2-converting cultures from cow manure were applied as inoculums for syngas fermentation. Gas and volatile fatty acids contents were measured by a gas chromatograph. We used 454 pyrosequencing and qPCR assay to reveal the community structure during the bioconversion. [Results] Acetate, ethanol and butyrate accumulated in cow manure and waste activated sludge during the incubation under H2/CO2 headspace with final acetate concentrations of approximately 63 mmol/L and 40 mmol/L, respectively, significantly higher than that of 3 mmol/L and 16 mmol/L in freshwater sediment and anaerobic methanogenic sludge. Diverse types of acetogens were found in waste activated sludge and cow manure. The major putative acetogens belonged to the species Clostridium spp., Sporomusa malonica and Acetoanaerobium noterae in waste activated sludge, and to Clostridium spp., Treponema azotonutricium and Oxobacter pfennigii in cow manure. [Conclusion] Both the richness and the number of acetogens were important factors for the bioconversion of H2/CO2 by mixed cultures. Enriched H2/CO2-converting cultures can use syngas as carbon source to produce acetate and ethanol.