Chlorinated ethenes are toxic and carcinogenic compounds that have contaminated a large quantity of groundwater in the US and other developed countries. In order to protect public health, in situ bioremediation via dehalorespiration by Dehalococcoides bacteria is a promising solution. The overall goal of this research is to explore the fundamental physiology of Dehalococcoides species and develop effective biomarkers for in situ monitoring in contaminated field sites. To accomplish these goals, the sequenced genome of Dehalococcoides ethenogenes strain 195 was used to guide hypotheses development and molecular and stable carbon isotope techniques were applied.
One objective of this research was to expand our current knowledge of the physiology of Dehalococcoides species. A nitrogenase operon is present in strain 195 and experimental evidence in this study demonstrated that strain 195 is capable of fixing atmospheric dinitrogen. However, this energy-expensive reaction came at the expense of reduced metabolic activity, which implied there might be negative consequences for bioremediation processes if the in situ cellular nutrient requirement is not monitored.
In order to effectively monitor the cellular metabolic activity on a real-time basis, the transcriptional expression of the reductive dehalogenase (RDase)-encoding tceA and vcrA genes, the proteins that enable Dehalococcoides bacteria to respire chlorinated ethenes, was characterized in a Dehalococcoides-containing enrichment. Overall, RDase gene expression correlated to the presence of chlorinated ethenes and active dechlorination, and a transcript half-life of four to six hours suggested that they can act as a real-time biomarker of metabolic activity.
The feasibility of applying molecular biomarkers in the environment was further researched in a chlorinated ethene-contaminated field site. Measurement of the characterized RDase-gene concentrations indicated different growth dynamics among Dehalococcoides strains and quantification of transcripts in the groundwater samples verified that the Dehalococcoides spp. were active. These results suggested that analyzing nucleic acids collected from the environment can provide useful information about the physiology of key organisms.
In addition to researching molecular biomarkers, stable carbon isotope fractionation of chlorinated ethenes by Dehalococcoides spp. was investigated to develop another line of evidence to indicate biological activity at field sites. Isotopic data from Dehalococcoides isolates revealed large variations in fractionation patterns among isolates and cautioned that care must be taken when incorporating isotope data into transport models to avoid inaccurate predictions of bioremediation activity.
The significance of this research is improving methods for optimization of bioremediation processes by eliminating potential bottlenecks in cell metabolism and obtaining accurate feedback information from cells that are indicative of their physiology. Knowledge developed in this research will aid practitioners to better design, monitor and optimize future in situ bioremediation systems.
|School:||University of California, Berkeley|
|School Location:||United States -- California|
|Source:||DAI-B 69/03, Dissertation Abstracts International|
|Keywords:||Bioremediation, Chlorinated ethenes, Chlorinated solvents, Dehalococcoides|
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