title: 16S rRNA metagenome associated with bioreactors: Sample T5 Planktonic
design: Electrical current can be used to supply reducing power to microbial metabolism. This phenomenon is typically studied in pure cultures with added redox mediators to transfer charge. Here, we investigate the development of a current-fed mixed microbial community fermenting glycerol at the cathode of a bioelectrochemical system in the absence of added mediators and identify correlations between microbial diversity and the respective product outcomes. Within one week of inoculation, a Citrobacter population represented 95-99% of community and the metabolite profiles were dominated by 1,3-propanediol and ethanol. Over time the Citrobacter population decreased in abundance while that of a Pectinatus population and the formation of propionate increased. After six weeks, several Clostridium populations and the production of valerate increased, which suggests that chain elongation was being performed. Current supply was stopped after nine weeks and was associated with a decrease in glycerol degradation and alcohol formation. This decrease was reversed by resuming current supply; however, when hydrogen gas was bubbled through the reactor during open circuit operation (OCP) as an alternative source of reducing power, glycerol degradation and metabolite production was unaffected. Cyclic voltammetry revealed that the community appeared to catalyse the hydrogen evolution reaction, leading to a +400 mV shift in its onset potential. Our results clearly demonstrate that current supply can alter fermentation profiles; however, further work is needed to determine the mechanisms behind this effect. In addition, operational conditions must be refined to gain greater control over community composition and metabolic outcomes. Data were demultiplexed by barcode using a shell script that allowed for only perfect matches.