| A trichloroethene (TCE)-dechlorinating/methanogenic mixed culture derived from a TCE-contaminated landfill site was characterized to better understand the roles and behaviors of microorganisms during microbial reductive dechlorination. The mixed culture dechlorinated TCE, via cis-DCE, 1,1-DCE and VC, to ethene with H2 as an electron donor.; Polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) analyses indicated that Dehalococcoides ethenogenes, a TCE-respiring bacterium, was present in the mixed culture and was most likely responsible for the dechlorination. The dominant methanogen was Methanosaeta concilii, a strictly acetoclastic methanogen, suggesting that a homoacetogen was present in the mixed culture. D. ethenogenes probably competed for H2 with the homoacetogen rather than the methanogen. The DGGE analyses showed at least four other dominant bacterial species in the mixed culture, although their exact identities and roles were less clear. The culture's dechlorinating and methanogenic activities were consistent with the PCR-DGGE results. Long-term exposure to 2-bromoethane sulfonic acid (BES), a methanogenesis inhibitor, was shown to affect bacteria in addition to methanogens. D. ethenogenes was not affected by BES, as indicated by the PCR result.; Effects of TCE concentration and pH on dechlorination and methanogenesis were investigated. With H2 as a sole electron donor, complete dechlorination to ethene was observed at TCE saturation as high as 20%. No dechlorination occurred at 50% saturation. Methanogenesis was inhibited by high TCE concentration. D. ethenogenes and M. concilii activities were observed in the pH range of 5.5 to 7.9, whereas pH 8.5 or higher was completely inhibitory to both. D. ethenogenes may have an advantage over its competitors at high TCE concentrations, whereas pH may not provide such advantage.; A column experiment was conducted to test the potential of Fe(0) as a H2 precursor to support microbial TCE dechlorination and methanogenesis. Little TCE dechlorination or methanogenesis were observed, whereas sulfate-reducing bacteria (SRB) appeared to dominate in the column. This result suggested that SRB need to be considered as a major player when Fe(0) is used as the sole electron sources for microorganisms. |
