Fig. 1. A schematic overview of the three performed experiments.

Events during the experiments such as medium refreshments, test for methane-dependent current, cyclic voltammetry (CV) and polarisation scans, activity test, and sampling for metagenomics and metatranscriptomics analysis as well as microscopy visualization are indicated. All systems in Experiment 1 were run in biological triplicate; RNA samples were collected at 0 mV in triplicate (2 biological, 1 technical replicate; n = 2), at 200 mV in triplicate (3 biological replicates, n = 3), at 400 mV in quadruplicate (3 biological replicates, 1 technical replicate, n = 3), at 600 mV in quadruplicate (3 biological replicates, 1 technical replicate, n = 3), and under nitrate growth in triplicate (3 biological replicates, n = 3). The differences in RNA samples for transcriptomics were a result of low amounts of biomass obtained and challenges associated with RNA extraction in archaea. DNA extraction for metagenomics was performed from one bioanode per experimental condition in experiment 1, and once during experiment 2.