“…For example, C. ljungdahlii was able to cometabolize CO 2 and H 2 to acetate and ethanol, which can be used for the production of butyrate and caproic acid by C. kluyveri (Richter, Molitor, Diender, Sousa, & Angenent, ). Another synergistic interaction is the interspecies hydrogen transfer (Thauer, Kaster, Seedorf, Buckel, & Hedderich, ), as the existence of many hydrogen producing Clostridium bacteria and methanogenic archaea in the SFB ecosystem (Ding et al., , , ; Hu et al., ; Li et al., ; Luo et al., ; Tao et al., ; Wu, Ding, Huang, & Zhou, ; Zheng et al., ). Interspecies hydrogen transfer between Clostridium and methanogenic archaea is beneficial to maintain the stability of the community and niches and also for the forming of many valuable metabolites (Hu et al., ).…”