Electromethanogenic biocathode spatial variability

Understanding microbial community assembly helps in determining the main drivers shaping a community in a particular environment, in this case the niche environment at the cathode of an electromethanogenic reactor. Triplicate methanogenic biocathodes were enriched in microbial electrolysis cells (MEC) for 5 months, then transferred to triplicate dual-chambered microbial electrosynthesis (MES) reactors, operated at –1.0 V vs. Ag/AgCl for six batches. At the end of the experiment, triplicate samples were taken at different positions (top, center, bottom) from each biocathode for a total of 9 samples for total biomass protein analysis and 16S rRNA gene amplicon sequencing. Microbial community analyses showed that overall the biocathodes were enriched with methanogens, especially the hydrogenotrophic family Methanobacteriaceae, Methanobacterium sp., the acetoclastic Methanosarcina sp., and the methylotrophic Methanomassillicoccus sp., with an overall core community representing >97% of sequence reads in all samples. There was statistically no significant spatial variability (p > .05) observed in the distribution of these communities within and between the reactors. These results suggest deterministic community assembly and indicate the reproducibility of electromethanogenic biocathodic communities, with implications for larger-scale reactors.