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Appl. Environ. Microbiol. doi:10.1128/AEM.01639-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Bacterial electrode reducing activities of Geobacter sulfurreducens compared to an enriched consortium in an air-cathode microbial fuel cell

Institute for Biological Resource and Functions, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1, Higashi, Tsukuba, Ibaraki 305-8566, Japan; Research Center for Advanced Science and Technology, University of Tokyo, 4-6-1, Komaba, Tokyo 153-8904, Japan; Department of Civil and Environmental Engineering, Penn State University, University Park, PA, 16802, USA; JSPS, 1-6, Chiyoda-ku, Tokyo 102-8471, Japan; Hashimoto Light Energy Conversion Project, ERATO, JST, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan

^* To whom correspondence should be addressed. Email: shunichi-ishii{at}aist.go.jp.

	Abstract

An electricity generating bacterium, Geobacter sulfurreducens PCA, was inoculated into an air-cathode single-chamber microbial fuel cell (MFC) in order to determine the maximum electron transfer rate from bacteria to the anode. To create anodic reaction-limiting conditions, where electron transfer from bacteria to the anode is the rate-limiting step, anodes with electrogenic biofilms were reduced in size and tests conducted using anodes of six different sizes. The smallest anode (7 cm², or the 1.5 times larger than the cathode) achieved an anodic reaction-limiting condition as a result of a limited mass of bacteria on the electrode. Under these conditions, the limiting current density reached a maximum of 1530 mA/m², and power density reached a maximum of 461 mW/m². Per-biomass efficiency of the electron transfer rate was constant at 32 fmol cell^-1 d^-1 (178 µmol g-protein^-1 min^-1), a rate comparable to that with solid iron as the electron acceptor but slower than rates achieved with fumarate or soluble iron. In comparison, an enriched electricity-generating consortium reached 374 µmol g-protein^-1 min^-1 under the same conditions, suggesting that the consortium had a much greater capacity for electrode reduction. These results demonstrate that per-biomass electrode reducing rates (calculated by current density and biomass density on the anode) can be used to help make better comparisons of electrogenic activity in MFCs.