초록
<P>The cathode microbial community of a methanogenic bioelectrochemical system (BES) is key to the efficient conversion of carbon dioxide (CO<SUB>2</SUB>) to methane (CH<SUB>4</SUB>) with application to biogas upgrading. The objective of this study was to compare the performance and microbial community composition of a biocathode inoculated with a mixed methanogenic (MM) culture to a biocathode inoculated with an enriched hydrogenotrophic methanogenic (EHM) culture, developed from the MM culture following pre-enrichment with H<SUB>2</SUB> and CO<SUB>2</SUB> as the only externally supplied electron donor and carbon source, respectively. Using an adjacent Ag/AgCl reference electrode, biocathode potential was poised at −0.8 V (versus SHE) using a potentiostat, with the bioanode acting as the counter electrode. When normalized to cathode biofilm biomass, the methane production in the MM- and EHM-biocathode was 0.153 ± 0.010 and 0.586 ± 0.029 mmol CH<SUB>4</SUB>/mg biomass-day, respectively. This study showed that H<SUB>2</SUB>/CO<SUB>2</SUB> pre-enriched inoculum enhanced biocathode CH<SUB>4</SUB> production, although the archaeal communities in both biocathodes converged primarily (86–100%) on a phylotype closely related to <I>Methanobrevibacter arboriphilus</I>. The bacterial community of the MM-biocathode was similar to that of the MM inoculum but was enriched in Spirochaetes and other nonexoelectrogenic, fermentative Bacteria. In contrast, the EHM-biocathode bacterial community was enriched in Proteobacteria, exoelectrogens, and putative producers of electron shuttle mediators. Similar biomass levels were detected in the MM- and EHM-biocathodes. Thus, although the archaeal communities were similar in the two biocathodes, the difference in bacterial community composition was likely responsible for the 3.8-fold larger CH<SUB>4</SUB> production rate observed in the EHM-biocathode. Roles for abundant OTUs identified in the biofilm and inoculum cultures were highlighted on the basis of previous reports.</P><P><B>Graphic Abstract</B><BR><IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/esthag/2017/esthag.2017.51.issue-9/acs.est.6b04112/production/images/medium/es-2016-041126_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/es6b04112'>ACS Electronic Supporting Info</A></P>