title: Microbial community structure in a biofilm anode fed with a fermentable substrate: the significance of hydrogen scavengers.
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 H(2)-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.
authors.affiliation: Center for Environmental Biotechnology, The Biodesign Institute at Arizona State University, AZ, USA.
authors.forename: Prathap
authors.initials: P
authors.lastname: Parameswaran
authors.forename: Husen
authors.initials: H
authors.lastname: Zhang
authors.forename: César I
authors.initials: CI
authors.lastname: Torres
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Rittmann
authors.forename: Rosa
authors.initials: R
authors.lastname: Krajmalnik-Brown
mesh_terms: D001419:Bacteria / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D018441:Biofilms; D004566:Electrodes / Q000382:microbiology; D005574:Formate-Tetrahydrofolate Ligase / Q000235:genetics; D006859:Hydrogen / Q000378:metabolism*; D012336:RNA, Ribosomal, 16S / Q000235:genetics
chemical_list: D012336:RNA, Ribosomal, 16S; D006859:Hydrogen; D005574:Formate-Tetrahydrofolate Ligase