Pathway and Enzymology of Cyclic Ether Biodegradation by Mycobacterium vaccae JOB5

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Title: Pathway and Enzymology of Cyclic Ether Biodegradation by Mycobacterium vaccae JOB5
Author: Lan, Renny Shang-Lun
Advisors: Jonathan Olson, Committee Member
Francis L. de los Reyes III, Committee Member
Michael R. Hyman, Committee Chair
Amy Grunden, Committee Member
Abstract: In this study we investigated the cometabolic oxidation of tetrahydrofruran (THF), 1,4-dioxane (14D) and other cyclic ethers by alkane-grown Mycobacterium vaccae JOB5. An initial screening demonstrated this strain oxidized all six ethers tested after growth on propane, n-butane, n-pentane, isobutane and isopentane. Ether-degrading activity was limited in dextrose-grown cells or in alkane-grown cells incubated with ethers and acetylene. Oxidation of THF and 14D was further characterized using propane-grown cells. Propane competitively inhibited THF oxidation and γ-butyrolactone (γBL) accumulated and was also consumed during THF oxidation. In contrast, no products were detected during 14D oxidation. Oxidation of γBL and the 3-hydroxy homolog of its unstable but presumed precursor, 2-hydroxytetrahydrofuran, were largely unaffected by acetylene. This suggested other enzymes co-expressed with the acetylene-sensitive, propane-oxidizing monooxygenase contributed to THF oxidation. Although strain JOB5 did not grow on any cyclic ethers tested, slight growth was observed with several lactones while vigorous growth was supported by 4-hydroxybutyrate, the expected immediate product of γBL degradation. The ability of strain JOB5 to assimilate THF metabolites during growth on n-alkanes was examined in carbon-limited batch cultures. Relative to growth on n-pentane alone, the final culture density and protein concentration were doubled in the presence of THF while no stimulation was observed with 14D. Our results are discussed in terms of the overlap between the enzymes and pathway involved in alkane and ether oxidation, their significance to our understanding of cometabolism and their potential impact on approaches for cyclic ether biodegradation in the environment.
Date: 2007-03-22
Degree: MS
Discipline: Microbiology

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