A novel ecological role of the Firmicutes identified in thermophilic microbial fuel cells

Authors

• Kelly C. Wrighton, University of California, Berkeley
• Peter Agbo, University of California, Berkeley,
• Falk Warnecke, DOE Joint Genome Institute, Walnut Creek, CA,
• Karrie A. Weber, University of Nebraska-LincolnFollow
• Eoin L. Brodie, Lawrence Berkeley National LaboratoryFollow
• Todd Z. DeSantis, Lawrence Berkeley National LaboratoryFollow
• Philip Hugenholtz, DOE Joint Genome Institute, Walnut Creek, CA
• Gary L. Andersen, Lawrence Berkeley National LaboratoryFollow
• John D. Coates, University of California, BerkeleyFollow

Document Type

Article

Date of this Version

2008

Citation

The ISME Journal (2008) 2, 1146–1156; doi:10.1038/ismej.2008.48

Comments

This article is a U.S. government work, and is not subject to copyright in the United States.

Abstract

Significant effort is currently focused on microbial fuel cells (MFCs) as a source of renewable energy. Most studies concentrate on operation at mesophilic temperatures. However, anaerobic digestion studies have reported on the superiority of thermophilic operation and demonstrated a net energy gain in terms of methane yield. As such, our studies focused on MFC operation and microbiology at 55 °C. Over a 100-day operation, these MFCs were stable and achieved a power density of 37mW m^–2 with a coulombic efficiency of 89%. To infer activity and taxonomic identity of dominant members of the electricity-producing community, we performed phylogenetic microarray and clone library analysis with small subunit ribosomal RNA (16S rRNA) and ribosomal RNA gene (16S rDNA). The results illustrated the dominance (80% of clone library sequences) of the Firmicutes in electricity production. Similarly, rRNA sequences from Firmicutes accounted for 50% of those taxa that increased in relative abundance from current-producing MFCs, implying their functional role in current production. We complemented these analyses by isolating the first organisms from a thermophilic MFC. One of the isolates, a Firmicutes Thermincola sp. strain JR, not only produced more current than known organisms (0.42 mA) in an H-cell system but also represented the first demonstration of direct anode reduction by a member of this phylum. Our research illustrates the importance of using a variety of molecular and culture-based methods to reliably characterize bacterial communities. Consequently, we revealed a previously unidentified functional role for Gram-positive bacteria in MFC current generation.