ERDC/CRREL TR-12-2 "Community Composition of Bacterial Biofilms Formed on Simple Soil Based Bioelectrochemical-chemical Cell Anodes and Cathodes"

Microbial fuel cells (MFC), as bioelectrochemical systems, hold promise as a sustainable source of energy for use in novel environments and settings. Although electrode biofilms, both anode and cathode, are critical to the production of power in these systems, the taxonomies of the biofilms that form are not fully understood. The specific objectives of the current study were to classify the bacteria that enriched onto fuel cell electrodes, with three biogeochemically distinct surface soils serving as the inocula. Following 1000 hours of incubation under saturated soil conditions, the community composition of the anode and cathode bacterial biofilms was quantified by culture, fatty acid profile (FA), and terminal restriction fragment length polymorphisms (TRFLP). The three soils produced open circuit voltages of between 60 and 120 mV, but only one soil maintained voltage under resistance (60 mV at 10,000 Ω). Fatty acid profiling identified differences among anode, cathode, and bulk soil microbial communities, specifically a greater relative abundance of terminally branched saturated FA in the bulk soils and a greater relative abundance of monounsaturated and cyclopropane FA on electrode surfaces. Bacteria cultured from both the anode and cathode biofilms included species of Actinobacteria; however, only the anode biofilms produced species of Firmicutes and Proteobacteria. Analysis of TRFLP profiles putatively identified a diversity of bacteria in the biofilms recovered from both electrode surfaces. The most predominant organisms detected were the αand ß-Proteobacteria, specifically the Rhizobiales, Rhodobacterales, and Burkholderiales. Although the detection of similar community fingerprints on both anodes and cathodes was not anticipated, the diversity of organisms putatively identified indicated a complexity that would support a coupled nitrogen cycle, one capable of facilitating the transfer of electrons to the soil cell anodes and from the soil cell cathodes. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR. ERDC/CRREL TR-12-2 iii