Microbial community structure in a biofilm anode fed with a fermentable substrate: The significance of hydrogen scavengers

Authors

  • Prathap Parameswaran,

    1. Center for Environmental Biotechnology, The Biodesign Institute at Arizona State University; telephone: 1-480-727-7574; fax: 1-480-727-0889
    Search for more papers by this author
  • Husen Zhang,

    1. Center for Environmental Biotechnology, The Biodesign Institute at Arizona State University; telephone: 1-480-727-7574; fax: 1-480-727-0889
    Search for more papers by this author
  • César I. Torres,

    1. Center for Environmental Biotechnology, The Biodesign Institute at Arizona State University; telephone: 1-480-727-7574; fax: 1-480-727-0889
    Search for more papers by this author
  • Bruce E. Rittmann,

    1. Center for Environmental Biotechnology, The Biodesign Institute at Arizona State University; telephone: 1-480-727-7574; fax: 1-480-727-0889
    Search for more papers by this author
  • Rosa Krajmalnik-Brown

    Corresponding author
    1. Center for Environmental Biotechnology, The Biodesign Institute at Arizona State University; telephone: 1-480-727-7574; fax: 1-480-727-0889
    • Center for Environmental Biotechnology, The Biodesign Institute at Arizona State University; telephone: 1-480-727-7574; fax: 1-480-727-0889.
    Search for more papers by this author

Abstract

We compared the microbial community structures that developed in the biofilm anode of two microbial electrolysis cells fed with ethanol, a fermentable substrate—one where methanogenesis was allowed and another in which it was completely inhibited with 2-bromoethane sulfonate. We observed a three-way syntrophy among ethanol fermenters, acetate-oxidizing anode-respiring bacteria (ARB), and a H2 scavenger. When methanogenesis was allowed, H2-oxidizing methanogens were the H2 scavengers, but when methanogenesis was inhibited, homo-acetogens became a channel for electron flow from H2 to current through acetate. We established the presence of homo-acetogens by two independent molecular techniques: 16S rRNA gene based pyrosequencing and a clone library from a highly conserved region in the functional gene encoding formyltetrahydrofolate synthetase in homo-acetogens. Both methods documented the presence of the homo-acetogenic genus, Acetobacterium, only with methanogenic inhibition. Pyrosequencing also showed a predominance of ethanol-fermenting bacteria, primarily represented by the genus Pelobacter. The next most abundant group was a diverse community of ARB, and they were followed by H2-scavenging syntrophic partners that were either H2-oxidizing methanogens or homo-acetogens when methanogenesis was suppressed. Thus, the community structure in the biofilm anode and suspension reflected the electron-flow distribution and H2-scavenging mechanism. Biotechnol. Bioeng. 2010;105: 69–78. © 2009 Wiley Periodicals, Inc.

Ancillary