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School of Civil and Environmental Engineering
Ph.D. Thesis Defense Announcement
Denitration of Nitroarene and Nitrate Ester Pollutants
By
Fei He
Advisor:
Dr. Jim C. Spain
Committee Members:
Dr. Joe Hughes (Drexel University), Dr. Spyros G. Pavlostathis (CEE),
Dr. Yongsheng Chen (CEE), Dr. Thomas DiChristina (BIO)
Date & Time: Monday, May 9, 2016, 10 AM
Location: Environmental Science and Technology Building 1177
Nitroaromatics and other nitrated compounds are a group of industrial chemicals extensively used in the synthesis of dyes, pesticides, pharmaceuticals and explosives, and have become contaminants widespread in soil and groundwater during manufacturing, handling and storage. The degradation of nitroglycerin (NG) has been reported but the degradation mechanism is not well established. Moreover, the biodegradability of some recalcitrant explosives such as such 2,6-dinitroxyelene (2,6-DNX) and 3,5-DNX and their environmental fate are poorly understood, which present challenges to ongoing efforts to bioremediate soils at contaminated sites. Therefore, the overall objectives of thesis were to investigate the degradability and the catabolic pathways of DNX isomers and NG.
NG degradation pathway in Arthrobacter JBH1 is rigorously established in this study. Two flavoproteins from the Old Yellow Enzyme (OYE) family, PfvA and PfvC, are involved in the sequential denitration of NG to 1-mononitroglycerin (1-MNG) and 2-MNG. The phosphorylation of 1-MNG by a glycerol kinase homolog facilitates one of the flavoproteins, PfvC, to remove the last nitrate ester group and produce 3-phosphoglycerol, which is readily to enter the central metabolism. Understanding the molecular basis of mineralization mechanisms of NG in JBH1, allows for the development of treatment strategies by overcoming the bottlenecks of the NG denitration process.
This study also demonstrates that 2,6-DNX and 3,5-DNX can be subject to oxidative attack when dioxygenases are present, however, the dominant reaction of DNX isomers was reduction. Microcosm studies with soil from contaminated sites carried out under different redox conditions show that 2,6-DNX and 3,5-DNX are reduced to aminonitroxylenes by soil bacteria when external carbon/energy sources are provided. These findings suggest that biostimulation could be an effective way to remediate DNX contamination. The reduction of DNX by juglone in the presence of hydrogen sulfide under abiotic conditions was also established. One electron-transfer potentials were determined for the DNX isomers, and structure-activity relationships were established, advancing the understanding of reductive transformation process of DNX and the transformation products in a given natural system, and prediction of the fate of the compounds in soil.
This study broadens the understanding of the effect of substituents on biodegradability of polyphenol, polynitroaromatic compounds, and provides a basis for development of remediation strategies to clean up the contaminants in soil and ground water.
