autotrophic metabolism and gradually to select for those bacte- ria able to fix CO2. After cessation of substrate addition, current consumption in the biotic reactors increased until day 16 then decreased until day 20 (Fig. 2a). On day 20 current consumption increased again and then stabilized around day 25 until the end of BES operation, suggesting biocathodic activity due to autotrophic metabolism. Pre-enrichment with glucose enhanced start-up time for development of an electrotrophic community compared to direct inoculation of reactors with the same bog sediment inocu- lum where no substantial current uptake was observed for more than 35 days (Fig. S2).
Maximum current density uptake for pre-enriched biotic reac- tors was −34 ± 4 mA/m2 and maximum electrons consumed expressed in Coulombs were 186 ± 19 over a period of 54 days of operation after a two-week start-up phase. The sustained negative current density that was recorded after approximately 25 days was on average −29 ± 6 mA/m2 and did not differ significantly between the replicate reactors (t-test; p = 0.005).
The highest power density consumed was −58 ± 8 mW/m2 . For the sterile control reactor, there was no appreciable change in current density uptake and electron consumption throughout the course of BES operation (Fig. 2a and b).