Microbial community structure in a biofilm anode fed with a fermentable substrate: The significance of hydrogen scavengers
✍ Scribed by Prathap Parameswaran; Husen Zhang; César I. Torres; Bruce E. Rittmann; Rosa Krajmalnik-Brown
- Publisher
- John Wiley and Sons
- Year
- 2010
- Tongue
- English
- Weight
- 425 KB
- Volume
- 105
- Category
- Article
- ISSN
- 0006-3592
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✦ Synopsis
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 H~2~ scavenger. When methanogenesis was allowed, H~2~‐oxidizing methanogens were the H~2~ scavengers, but when methanogenesis was inhibited, homo‐acetogens became a channel for electron flow from H~2~ 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 H~2~‐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 H~2~‐scavenging mechanism. Biotechnol. Bioeng. 2010;105: 69–78. © 2009 Wiley Periodicals, Inc.