| The Role of Syntrophic Associations in Sustaining Anaerobic Mineralization of Chlorinated Organic Compounds Jennifer G. Becker, Gina Berardesco,* Bruce E. Rittmann,† and David A. Stahl‡ Department of Civil and Environmental Engineering, Northwestern University, Evanston, Illinois, USA Abstract
Stable associations of syntrophic fermentative organisms and populations that consume fermentation products play key roles in the anaerobic biodegradation of chlorinated organic contaminants. The involvement of these syntrophic populations is essential for mineralization of chlorinated aromatic compounds under methanogenic conditions. The fermentative production of low levels of hydrogen (H2) can also be used to selectively deliver a limiting electron donor to dehalogenating organisms and achieve complete dehalogenation of chlorinated aliphatic contaminants such as tetrachloroethene. Thus, tracking the abundance of syntrophically coupled populations should aid in the development and monitoring of sustainable bioremediation strategies. In this study, two complementary nucleic acid-based methods were used to identify and assess relative changes or differences in the abundance of potentially important populations in complex anaerobic microbial communities that mineralized chlorinated aromatic compounds. Population dynamics were related to the consumption and production of key metabolic substrates, intermediates, and products. Syntrophus-like populations were detected in 3-chlorobenzoate-degrading communities derived from sediment or sludge digesters. In the presence of H2-consuming populations, characterized Syntrophus species ferment benzoate, a central intermediate in the anaerobic metabolism of 3-chlorobenzoate and 2-chlorophenol. A DNA probe that targeted characterized Syntrophus species was developed and used to quantify rRNA extracted from the 3-chlorobenzoate- and 2-chlorophenol-degrading communities. The level of rRNA targeted by the Syntrophus-specific probe tracked with the formation of benzoate during metabolism of the parent compounds. Hybridizations with an Archaea-specific probe and/or measurement of methane production demonstrated that methanogens directly benefited from the influx of benzoate-derived electron donors, and the activities of Syntrophus-like and methanogenic populations in the contaminant-degrading communities were closely linked. Key words: 2-chlorophenol, 3-chlorobenzoate, benzoate, bioremediation, microbial communities, oligonucleotide probes, reductive dechlorination, ribosomal RNA, syntrophic associations, Syntrophus. Environ Health Perspect 113:310-316 (2005) . doi:10.1289/ehp.6933 available via http://dx.doi.org/ [Online 8 December 2004]
This article is based on a presentation at the conference "Bioremediation and Biodegradation: Current Advances in Reducing Toxicity, Exposure and Environmental Consequences" (http://www-apps.niehs.nih.gov/sbrp/bioremediation.html) held 9-12 June 2002 in Pacific Grove, California, and sponsored by the NIEHS Superfund Basic Research Program. The overall focus of this conference was on exploring the research interfaces of toxicity reduction, exposure assessment, and evaluation of environmental consequences in the context of using state-of-the-art approaches to bioremediation and biodegradation. The Superfund Basic Research Program has a legacy of supporting research conferences designed to integrate the broad spectrum of disciplines related to hazardous substances. Address correspondence to J.G. Becker, Department of Biological Resources Engineering, University of Maryland, Building 142, College Park, MD 20742-2315 USA. Telephone: (301) 405-1179. Fax: (301) 314-9023. E-mail: jgbecker@wam.umd.edu *Present address: zuChem, Inc., Chicago, IL 60610 USA. †Present address: Center for Environmental Biotechnology, Biodesign Institute, Arizona State University, Tempe, AZ 85287-5801 USA. ‡Present address: Department of Civil and Environmental Engineering, University of Washington, Seattle, WA 98195 USA. We thank V. Denef for his contributions as a rapporteur at the conference. We also appreciate the assistance of the Clavey Road Wastewater Treatment Plant personnel in obtaining samples of the digester contents. This research was supported by the U.S. Environmental Protection Agency Science to Achieve Results (S.T.A.R.) grant R823351 to D.A.S. and B.E.R. The authors declare they have no competing financial interests. Received 23 December 2003 ; accepted 17 June 2004.
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