A biofilm anode acclimated with growth media containing acetate, then acetate + methane, and finally methane alone produced electrical current in a microbial electrochemical cell (MxC) fed with methane as the sole electron donor. Geobacter was the dominant genus for the bacterial domain (93%) in the biofilm anode, while methanogens (Methanocorpusculum labreanum and Methanosaeta concilii) accounted for 82% of the total archaeal clones in the biofilm. Fluorescence in situ hybridization (FISH) imaging clearly showed a biofilm of mixed bacteria and archaea, suggesting a syntrophic interaction between them for performing anaerobic oxidation of methane (AOM) in the biofilm anode. Measured cumulative coulombs were linearly correlated to the methane-gas concentration in the range of 10-99.97% (R-2 >= 0.99) when the measurement was sustained for at least 50 min Thus, cumulative coulombs over 50 min could be used to quantify the methane concentration in gas samples. (C) 2017 Elsevier Ltd. All rights reserved.