초록
<P>Methane is the primary end product from cathodic current in microbial electrolysis cells (MECs) in the absence of methanogenic inhibitors, but little is known about the archaeal communities that develop in these systems. MECs containing cathodes made from different materials (carbon brushes, or plain graphite blocks or blocks coated with carbon black and platinum, stainless steel, nickel, ferrihydrite, magnetite, iron sulfide, or molybdenum disulfide) were inoculated with anaerobic digester sludge and acclimated at a set potential of −600 mV (versus a standard hydrogen electrode). The archaeal communities on all cathodes, except those coated with platinum, were predominated by <I>Methanobacterium</I> (median 97% of archaea). Cathodes with platinum contained mainly archaea most similar to <I>Methanobrevibacter</I>. Neither of these methanogens were abundant (<0.1% of archaea) in the inoculum, and therefore their high abundance on the cathode resulted from selective enrichment. In contrast, bacterial communities on the cathode were more diverse, containing primarily δ-<I>Proteobacteria</I> (41% of bacteria). The lack of a consistent bacterial genus on the cathodes indicated that there was no similarly selective enrichment of bacteria on the cathode. These results suggest that the genus <I>Methanobacterium</I> was primarily responsible for methane production in MECs when cathodes lack efficient catalysts for hydrogen gas evolution.</P><P><I>Methanobacterium</I> was enriched on all electrodes set at −600 mV except those containing platinum or electrodes set at open circuit.</P><P><B>Graphic Abstract</B><BR><IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ascecg/2015/ascecg.2015.3.issue-7/acssuschemeng.5b00367/production/images/medium/sc-2015-003672_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/sc5b00367'>ACS Electronic Supporting Info</A></P>