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

• Published in: The ISME Journal 2008-11, Vol.2 (11), p.1146-1156
• Main Authors: Wrighton, Kelly C, Agbo, Peter, Warnecke, Falk, Weber, Karrie A, Brodie, Eoin L, DeSantis, Todd Z, Hugenholtz, Philip, Andersen, Gary L, Coates, John D
• Format: Article
• Language: English
• Subjects: Anaerobic digestion; Bacteria; Bioelectric Energy Sources - microbiology; Biomedical and Life Sciences; DNA, Bacterial - chemistry; DNA, Bacterial - genetics; DNA, Ribosomal - chemistry; DNA, Ribosomal - genetics; Ecology; Electric power generation; Electricity; Evolutionary Biology; Firmicutes; Fuel cells; Fuel technology; Genes, rRNA; Gram-Positive Bacteria - classification; Gram-Positive Bacteria - isolation & purification; Gram-Positive Bacteria - metabolism; Hot Temperature; Life Sciences; Methane; Microarray Analysis; Microbial Ecology; Microbial Genetics and Genomics; Microbiology; Molecular Sequence Data; original-article; Phylogeny; Relative abundance; Renewable energy sources; RNA, Bacterial - genetics; RNA, Ribosomal, 16S - genetics; Sequence Analysis, DNA; Sequence Homology, Nucleic Acid; Taxa
• ISSN: 1751-7362; 1751-7370
• DOI: 10.1038/ismej.2008.48

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.