title: A novel ecological role of the Firmicutes identified in thermophilic microbial fuel cells.
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 degrees C. Over a 100-day operation, these MFCs were stable and achieved a power density of 37 mW 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.
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley CA 94720, USA.
authors.forename: Kelly C
authors.initials: KC
authors.lastname: Wrighton
authors.forename: Peter
authors.initials: P
authors.lastname: Agbo
authors.forename: Falk
authors.initials: F
authors.lastname: Warnecke
authors.forename: Karrie A
authors.initials: KA
authors.lastname: Weber
authors.forename: Eoin L
authors.initials: EL
authors.lastname: Brodie
authors.forename: Todd Z
authors.initials: TZ
authors.lastname: DeSantis
authors.forename: Philip
authors.initials: P
authors.lastname: Hugenholtz
authors.forename: Gary L
authors.initials: GL
authors.lastname: Andersen
authors.forename: John D
authors.initials: JD
authors.lastname: Coates