Microbial Growth On Anthropogenic Compounds By Reductive Dehalogenation Or Oxidation

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The improper disposal of chlorinated organic compounds is a concern because of their toxicity and persistent nature. Dehalococcoides mccartyi strain 195 can reductively dehalogenate some of these compounds and, in the case of tetrachloroethene (PCE), detoxify it by producing ethene. Its genome contains a putative prophage, which could inhibit its ability to grow to high densities and cause phage mediated cell death. This phage was evaluated by genomic comparisons and electron microscopy. Cellular stress induced phage expression and stopped dechlorination. Dehalococcoides can partially dechlorinate polychlorinated benzenes but will not use dichlorobenzene. Three strains of Dehalobacter that are able to produce monochlorobenzene from dichlorobenzene (DCB) were sequenced and assembled. Analysis of their genomes shows metabolic specialization for growth by reductive dehalogenation. Their genomes were larger then Dehalococcoides spp. genomes but smaller then the nearest sequenced phylogenic relative, further indicating specialization. The process of reductive dechlorination does not completely explain the flux of chlorinated ethenes at contaminated sites. To investigate oxidation as an alternative metabolism, groundwater and sediment microcosm were amended with various electron acceptors and either vinyl chloride (VC) or ethene as electron donors. Determination of oxidation was monitored by gas chromatography for the loss of VC and ethene overtime without the production of ethene, ethane or methane. From the groundwater microcosms, a Mycobacterium was isolated that could oxidize VC at microaerobic levels, perhaps partially explaining the observed lack of mass balance. Growth was monitored visually and increased with the decrease in VC concentration. From the sediment microcosms, an enrichment culture was developed, with one dominant organism related to Desulfovirga adipica that was able to oxidize ethene coupled to sulfate reduction. Growth and metabolism in this enrichment culture was observed by quantative PCR and the production of sulfide.

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Reductive Dehalogenation; Chlorinated organic compounds
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Zinder, Stephen H
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Richardson, Ruth E.
Buckley, Daniel H
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Ph. D., Microbiology
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Doctor of Philosophy
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Government Document
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dissertation or thesis
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