Syntrophic interactions among anode respiring bacteria (ARB) and Non-ARB in a biofilm anode: electron balances

Authors

  • Prathap Parameswaran,

    Corresponding author
    1. Center for Environmental Biotechnology, The Biodesign Institute at Arizona State University, 1001 S McAllister Avenue, Tempe, Arizona; telephone: 1-480-727-0432; fax: 1-480-727-0889
    • Center for Environmental Biotechnology, The Biodesign Institute at Arizona State University, 1001 S McAllister Avenue, Tempe, Arizona; telephone: 1-480-727-0432; fax: 1-480-727-0889.
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  • César I. Torres,

    1. Center for Environmental Biotechnology, The Biodesign Institute at Arizona State University, 1001 S McAllister Avenue, Tempe, Arizona; telephone: 1-480-727-0432; fax: 1-480-727-0889
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  • Hyung-Sool Lee,

    1. Center for Environmental Biotechnology, The Biodesign Institute at Arizona State University, 1001 S McAllister Avenue, Tempe, Arizona; telephone: 1-480-727-0432; fax: 1-480-727-0889
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  • Rosa Krajmalnik-Brown,

    1. Center for Environmental Biotechnology, The Biodesign Institute at Arizona State University, 1001 S McAllister Avenue, Tempe, Arizona; telephone: 1-480-727-0432; fax: 1-480-727-0889
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  • Bruce E. Rittmann

    1. Center for Environmental Biotechnology, The Biodesign Institute at Arizona State University, 1001 S McAllister Avenue, Tempe, Arizona; telephone: 1-480-727-0432; fax: 1-480-727-0889
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Abstract

We demonstrate that the coulombic efficiency (CE) of a microbial electrolytic cell (MEC) fueled with a fermentable substrate, ethanol, depended on the interactions among anode respiring bacteria (ARB) and other groups of micro-organisms, particularly fermenters and methanogens. When we allowed methanogenesis, we obtained a CE of 60%, and 26% of the electrons were lost as methane. The only methanogenic genus detected by quantitative real-time PCR was the hydrogenotrophic genus, Methanobacteriales, which presumably consumed all the hydrogen produced during ethanol fermentation (∼30% of total electrons). We did not detect acetoclastic methanogenic genera, indicating that acetate-oxidizing ARB out-competed acetoclastic methanogens. Current production and methane formation increased in parallel, suggesting a syntrophic interaction between methanogens and acetate-consuming ARB. When we inhibited methanogenesis with 50 mM 2-bromoethane sulfonic acid (BES), the CE increased to 84%, and methane was not produced. With no methanogenesis, the electrons from hydrogen were converted to electrical current, either directly by the ARB or channeled to acetate through homo-acetogenesis. This illustrates the key role of competition among the various H2 scavengers and that, when the hydrogen-consuming methanogens were present, they out-competed the other groups. These findings also demonstrate the importance of a three-way syntrophic relationship among fermenters, acetate-consuming ARB, and a H2 consumer during the utilization of a fermentable substrate. To obtain high coulombic efficiencies with fermentable substrates in a mixed population, methanogens must be suppressed to promote new interactions at the anode that ultimately channel the electrons from hydrogen to current. Biotechnol. Bioeng. 2009;103: 513–523. © 2009 Wiley Periodicals, Inc.

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