N-219. Quantitation of Population Growth and Decay for Organisms Present in a Chloroethene Reducing enrichment Culture

A. R. Rowe, G. L. Heavner, R. E. Richardson;
Cornell Univ., Ithaca, NY.

In anaerobic systems, the dechlorination of chlorinated organic compounds like the common groundwater pollutants PCE and TCE, is mediated by microbial consortia. In these consortia organisms that reductively dechlorinate, specifically the Dehalococcoides group, rely on hydrogen from syntrophic fermentation, and as-yet undetermined biologically synthesized nutrients. Many phyla, such as members of the Firmicutes, delta/epsilon-Proteobacteria, Bacteroides, Thermotoga, Spirochetes and Methanogens are commonly represented in these communities as shown by 16S rDNA clone library analysis. However the specific roles or activities of these organisms, especially with respect to interactions with Dehalococcoides have yet to be established. In order to further understand the role of other organisms in these consortia, amendment cultures from a chloroethene degrading microbial enrichment were constructed to quantitatively track population growth and decay. These cultures were feed with different substrates. For example, cultures were fed nothing, acetate, formate, butyrate and H2, in either the presence or absence of PCE. Cultures were maintained from 4 to 16 weeks on a weekly feeding and wasting cycle. Production of methane, dechlorination end products, and production/consumption of organic acids were tracked using gas and ion chromatography. Population growth and decay was tracked using quantitative PCR. Results of unfed cultures suggest population decay rate for Dehalococcoides ethenogenes strain 195 of 0.068/per day. Methanogen populations decayed much slower (0.0057 or 0.002 for Methanospirillum and Methanosaeta, respectively) presumably because their growth substrates (H2 & acetate) were slowly released from decaying biomass. Primers for additional groups are being used to track growth yields and decay rates. The aim of this work is to construct a more refined model of how electrons flow through this enrichment culture, and generate hypotheses about the physiological roles of these other phylogenetic groups in dechlorinating communities.