Comparison of Different Carbon Sources on Biomethane Production with Clostridium cellulovorans and Methanogens

Methane (CH4) has attracted attention as not only one of the hydrogen carriers in terms of energy density, but also synthetic natural gas. In nature, the decomposition of organic compounds is performed with bacterial ecosystems that can produce CH4. Clostridium cellulovorans as a decomposer was cultivated with pig manure (PM) as an unused biomass in this study. As a result of high-performance liquid chromatography (HPLC) analysis, while formate and lactate were decreased in the C. cellulovorans medium containing 0.5% PM, acetate and butyrate were increased in it. Accordingly, in order to compare with the effect of carbon sources for methane production, the cocultivation of C. cellulovorans and the methanogenesis of Methanosarcina mazei or microbial flora of methane production (MFMP) was carried out in the C. cellulovorans medium. As a result, only the cocultivation with C. cellulovorans and MFMP showed methane production in 0.5% acetate medium. Moreover, in comparison with a carbon source in either 1% acetate or 1% methanol medium, MFMP was only cultivated after being precultivated with 0.5% glucose medium for 12 h. The results revealed that MFMP with a 1% methanol medium produced methane approximately eight times higher than with 1% acetate medium. After cultivation with 1% acetate or 1% methanol, next-generation sequencing (NGS) analysis of MFMP was carried out. Interestingly, Methanofollis (0.211%), belonging to methanogens through the CO2 reduction pathway, was dominant in the 1% acetate medium for 72 h cultivation, while Methanosarcina siciliae (1.178%), M. barkeri (0.571%), and Methanofollis (0.490%) were major species in 1% methanol medium for 72 h cultivation. Since Methanosarcina spp. belong to acetoclasts (acetoclastic pathway), methanol could promote the growth of Methanosarcina spp., rather than acetate. Therefore, it seems that Methanosarcina spp. may play a key methanogenesis role in MFMP. Thus, these results will provide important information for low-cost biomethane production.