Physiology and Enzymology of Aerobic MTBE and TBA Biodegradation

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Title: Physiology and Enzymology of Aerobic MTBE and TBA Biodegradation
Author: Golart, Kimberly Lee
Advisors: Francis de los Reyes III, Committee Member
Michael R. Hyman, Committee Chair
James W. Brown, Committee Member
Jonathan W. Olson, Committee Member
Abstract: Methyl tertiary butyl ether (MTBE), a widely used gasoline oxygenate, has been added to gasoline over the past 25 years to increase the octane rating and reduce air pollution from vehicle emissions. tertiary butyl alcohol (TBA) has also been used as a gasoline oxygenate and is a key intermediate in the biodegradation of MTBE. The frequent detection of these compounds as ground water contaminants has raised public health concerns and addresses the need for their remediation. This research focuses on the characterization of the physiology and enzymology of microorganisms able to grow on MTBE and TBA. In this study, we isolated and characterized two aerobic bacterial strains able to utilize TBA as a sole source of carbon and energy. Strains, Hydrogenophaga G2B2 and Aquincola S1B1 rapidly oxidized TBA, but were unable to grow on MTBE or oxidize MTBE after growth on TBA. Using a novel approach combining a fluorinated analog of TBA, 2-trifluoromethyl-2-propanol (TFMP), with 19F-nuclear magnetic resonance (19F-NMR) spectroscopy, we also report the detection of the initial TBA biodegradation pathway intermediates 2-methyl-1,2-propanediol (2M12PD) and 2-hydroxyisobutyric acid (2HIBA) with both strains S1B1 and G2B2. We also demonstrated the cometabolic oxidation of MTBE by a defined co-culture containing Pseudomonas mendocina KR1 and our isolate Aquincola S1B1. MTBE degradation was achieved through the n-alkane dependent cometabolic oxidation of MTBE by strain KR1 with the subsequent assimilation of TBA by strain S1B1. We also report the identification of polypeptides induced after the growth of strain S1B1 on TBA. Our initial results suggest that these proteins are enzymes associated with TBA oxidation in this strain. Our final study examined the biodegradation of MTBE by the MTBE-metabolizing strain Methylibium petroleiphilum PM1. Our results demonstrated that the MTBE biodegradation pathway of strain PM1 includes the intermediates TBA, 2M12PD, and 2HIBA. Furthermore, our results suggest that separate enzyme systems catalyze MTBE and TBA oxidation in this strain. We also identified a formaldehyde-activating protein in MTBE-grown cells, which may play a role in formaldehyde-detoxification during MTBE oxidation by strain PM1.
Date: 2008-10-23
Degree: PhD
Discipline: Microbiology
URI: http://www.lib.ncsu.edu/resolver/1840.16/5843


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