Subsurface aquifer sediment-derived bioanode metagenome sequencing and assembly. bioanode metagenome

There is growing recognition of the ability of microbes to interact electronically with each other and with minerals, in some cases causing the minerals to dissolve. Here we used a bio-electrochemical system in which a solid electrode served as a redox-active surface to enrich for anode-respiring consortia. The system was inoculated with anaerobic sediment and groundwater from a well-studied aquifer near Rifle, CO, and amended with acetate. Anode biofilms and planktonic samples were characterized by genome-resolved metagenomics. We reconstructed draft-quality and near-complete genomes for 84 bacteria and 2 archaea that represent the majority of organisms present in 28 samples. A novel Geobacter sp. with 72 multiheme c-type cytochromes (MHCs) was the dominant electrode-attached organism. However, Actinobacteria, Ignavibacteria, Chloroflexi, Acidobacteria, Firmicutes and Burkholderiales were also implicated in electrode respiration, based on genomes encoding cytochromes with ≥10 heme-binding motifs and porin cytochrome complexes. Most of these bacteria were abundant in anode-associated biofilms, but not in the planktonic fraction, over the two-year study period, consistent with the importance of these proteins for growth via extracellular electron acceptors. Our results identify a small subset of the thousands of organisms previously detected in this aquifer that may have the potential to mediate mineral redox transformations.