Relative abundances of genus-level phylogenetic groups based on pyrosequenced 16S rRNA-gene amplicons showing structures of bacterial communities in the original sludge, anode biofilm, cathode biofilm, and electrolyte.

<p>Relative abundances of genus-level phylogenetic groups based on pyrosequenced 16S rRNA-gene amplicons showing structures of bacterial communities in the original sludge, anode biofilm, cathode biofilm, and electrolyte.</p

Polarization (open squares) and power (closed squares) curves for the methanol-fed MFC.

<p>Polarization (open squares) and power (closed squares) curves for the methanol-fed MFC.</p

Catabolic pathway for methanol/acetate conversion in the methanol-fed MFC predicted from the metagenome data (A), and phylum-level distributions of genes assigned to each catabolic step (B).

<p>Step I, methanol:THF methyltransferase; II, acetyl-CoA synthase (EC.2.3.1.169); III, carbon monoxide dehydrogenase (EC.1.2.7.4); IV, acetyl-CoA synthetase (EC.6.2.1.1); V, phosphate acetyltransferase (EC.2.3.1.8); and VI, acetate kinase (EC.2.7.2.1).</p

Comparison of the total lengths of large contigs affiliated with different phyla as determined by MEGAN or BLSOM analyses of the metagenome data.

<p>Comparison of the total lengths of large contigs affiliated with different phyla as determined by MEGAN or BLSOM analyses of the metagenome data.</p

Metagenomic Analyses Reveal the Involvement of Syntrophic Consortia in Methanol/Electricity Conversion in Microbial Fuel Cells

<div><p>Methanol is widely used in industrial processes, and as such, is discharged in large quantities in wastewater. Microbial fuel cells (MFCs) have the potential to recover electric energy from organic pollutants in wastewater; however, the use of MFCs to generate electricity from methanol has not been reported. In the present study, we developed single-chamber MFCs that generated electricity from methanol at the maximum power density of 220 mW m⁻² (based on the projected area of the anode). In order to reveal how microbes generate electricity from methanol, pyrosequencing of 16S rRNA-gene amplicons and Illumina shotgun sequencing of metagenome were conducted. The pyrosequencing detected in abundance <i>Dysgonomonas</i>, <i>Sporomusa</i>, and <i>Desulfovibrio</i> in the electrolyte and anode and cathode biofilms, while <i>Geobacter</i> was detected only in the anode biofilm. Based on known physiological properties of these bacteria, it is considered that <i>Sporomusa</i> converts methanol into acetate, which is then utilized by <i>Geobacter</i> to generate electricity. This speculation is supported by results of shotgun metagenomics of the anode-biofilm microbes, which reconstructed relevant catabolic pathways in these bacteria. These results suggest that methanol is anaerobically catabolized by syntrophic bacterial consortia with electrodes as electron acceptors.</p></div

Typical time courses of cell voltage (A), methanol concentration (B), and acetate concentration (C), after supplementation of the MFC with 10 mM methanol.

<p>In panels B and C, data are means ± SD (n = 3), and error bars are shown when they are larger than symbols.</p

Gene clusters containing putative methanol:THF methyltransferases (black arrows) in metagenome contig NODE_348 and the genome of <i>Sporomusa ovata</i>.

<p>Possible genes encoding transcriptional regulators for methyltransferases are indicated with gray arrows. Results of BLAST search for the genes are described in the table.</p

Summary of numerical data for the metagenomic analyses of microbes associated with the anode biofilm in the methanol-fed MFC.

<p>Summary of numerical data for the metagenomic analyses of microbes associated with the anode biofilm in the methanol-fed MFC.</p

Distribution of microbes in the methanol-fed MFC.

<p>(A) Total protein contents showing amounts of microbes associated with the anode biofilm, cathode biofilm, and electrolyte. (B) Results of an anode-exchange experiment, in which cell voltages of methanol-fed MFCs were measured after the microbe-bearing anode was transferred to a reactor containing fresh electrolyte (black line) and a new anode was placed in the spent electrolyte of the initial reactor (gray line).</p

Metagenomic insights into the genus <i>Geobacter</i> obtained by MEGAN analyses.

<p>(A) Sub-genus level distribution of genes affiliated with the genus <i>Geobacter</i> based on BLAST homology. ‘<i>Geobacter</i>’ in the figures represents genes that were assigned to <i>Geobacter</i> at the genus level, but not to any genome-sequenced strain. (B) A partial MEGAN tree showing taxonomic distribution of genes encoding the acetate-catabolizing enzymes acetyl-CoA synthetase (EC 6.2.1.1), phosphate acetyltransferase (2.3.1.8), and acetate kinase (2.7.2.1), assigned to the class <i>Deltaproteobacteria</i>. LCA parameters: Min score, 50; top percent, 1.0; Min support, 2.</p