초록
<P><B>Background</B></P><P>The interspecies interactions in a biomethanation community play a vital role in substrate degradation and methane (CH<SUB>4</SUB>) formation. However, the physiological and molecular mechanisms of interaction among the microbial members of this community remain poorly understood due to the lack of an experimentally tractable model system. In this study, we successfully established two coculture models combining the cellulose-degrading bacterium <I>Clostridium cellulovorans</I> 743B with <I>Methanosarcina barkeri</I> Fusaro or <I>Methanosarcina mazei</I> Gö1 for the direct conversion of cellulose to CH<SUB>4</SUB>.</P><P><B>Results</B></P><P>Physiological characterizations of these models revealed that the methanogens in both cocultures were able to efficiently utilize the products produced by <I>C. cellulovorans</I> during cellulose degradation. In particular, the simultaneous utilization of hydrogen, formate, and acetate for methanogenesis was observed in the <I>C. cellulovorans</I>–<I>M. barkeri</I> cocultures, whereas monocultures of <I>M. barkeri</I> were unable to grow with formate alone. Enhanced cellulose degradation was observed in both cocultures, and the CH<SUB>4</SUB> yield of the <I>C. cellulovorans</I>–<I>M. barkeri</I> cocultures (0.87 ± 0.02 mol CH<SUB>4</SUB>/mol glucose equivalent) was among the highest compared to other coculture studies. A metabolic shift in the fermentation pattern of <I>C. cellulovorans</I> was observed in both cocultures. The expression levels of genes in key pathways that are important to the regulation and metabolism of the interactions in cocultures were examined by reverse transcription-quantitative PCR, and the expression profiles largely matched the physiological observations.</P><P><B>Conclusions</B></P><P>The physiological and molecular characteristics of the interactions of two CH<SUB>4</SUB>-producing cocultures are reported. Coculturing <I>C. cellulovorans</I> with <I>M. barkeri</I> or <I>M. mazei</I> not only enabled direct conversion of cellulose to CH<SUB>4</SUB>, but also stabilized pH for <I>C. cellulovorans</I>, resulting in a metabolic shift and enhanced cellulose degradation. This study deepens our understanding of interspecies interactions for CH<SUB>4</SUB> production from cellulose, providing useful insights for assembling consortia as inocula for industrial biomethanation processes.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/s13068-017-0719-y) contains supplementary material, which is available to authorized users.</P>