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

Kelly C. Wrighton, Peter Agbo, Falk Warnecke, Karrie A. Weber, Eoin L. Brodie, Todd Z. DeSantis, Philip Hugenholtz, Gary L. Andersen, John D. Coates

Research output: Contribution to journalArticlepeer-review

255 Scopus citations


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 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.

Original languageEnglish (US)
Pages (from-to)1146-1156
Number of pages11
JournalISME Journal
Issue number11
StatePublished - Nov 2008
Externally publishedYes


  • Anode
  • Biofilm
  • Biofuel
  • Extracellular electron transfer
  • Iron reduction

ASJC Scopus subject areas

  • Microbiology
  • Ecology, Evolution, Behavior and Systematics


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