Effects of Different Carbon Sources on Biomethane Production with <em>Clostridium Cellulovorans</em> and Methanogens

Abstract

Methane (CH4) has attracted attention as not only synthetic natural gas, but also one of the hy-drogen carriers in terms of energy density. On the other hand, there exist bacterial ecosystems in nature that can decompose organic compounds to produce CH4 and CO2. In this study, Clostridi-um cellulovorans was first cultivated with pig manure (PM) as an unused biomass. Regarding the measurement of organic acids by high-performance liquid chromatography (HPLC), acetate and butyrate were increased in the C. cellulovorans medium containing 0.5% PM, while formate and lactate were decreased in it. Next, in comparison with carbon sources such as glucose, cellobiose, and acetate, cocultivation of C. cellulovorans and Methanosarcina mazei or microbial flora of me-thane production (MFMP) was performed in the C. cellulovorans medium. These results revealed that 0.5% acetate as the sole carbon source produced CH4 only by cocultivating C. cellulovorans and MFMP. Furthermore, MFMP was only cultivated with 1% acetate or 1% methane as a carbon source after precultivated with 0.5% glucose medium for 12 h. As a result, methane productivity of MFMP with 1% methanol medium was approximately eight times higher than that with 1% acetate medium. Finally, next-generation sequencing (NGS) analysis of MFMP after cultivation with 1% acetate or 1% methane was carried out. Interestingly, Methanofollis (0.211%) belonging to H2/CO2 -using methanogens (CO2 reduction pathway) was dominant in the 1% acetate medium for 72 h cultivation, whereas Methanosarcina siciliae (1.178%), M. barkeri (0.571%), and Methano-follis (0.490%) were major species in 1% methanol medium for 72 h cultivation. Since Methano-sarcina spp. are belonging to acetoclasts (acetoclastic pathway), methanol could promote to grow Methanosarcina spp. rather than acetate. Therefore, it seemed Methanosarcina spp. may play a key methanogenesis in MFMP. Thus, these results will provide important information for low cost biomethane production.