Browsing by Subject "Naphthalene catabolism"
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Item Investigation of the ring-cleaving dioxygenase and hydratase-aldolase reactions in the Mycobacterium vanbaalenii PYR-1 catabolic pathways(2018-10-09) Erwin, Kaci Leigh; Whitman, Christian P.; Fast, Walter; Hoffman, David; Liu, Hung-wen; Zhang, YanPolycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants made of fused aromatic rings. The improper disposal of petrochemicals is a major source of PAHs in the environment. They are generally recalcitrant due to their stability and poor water solubility. Degradation of PAHs by bacteria and other microorganisms is one way to remove PAHs from contaminated environments. Mycobacterium vanbaalenii PYR-1 is the first identified bacterium with the ability to completely degrade pyrene. In addition, M. vanbaalenni PYR-1 can degrade a variety of PAHs and, in this regard, is the most nutritionally versatile bacteria isolated so far. The degradation of PAHs by M. vanbaalenni PYR-1 has been extensively studied with many proposed avenues leading to useful cellular intermediates. However, there is very little biochemical evidence for many of these pathways. The degradative pathways for naphthalene, phenanthrene, pyrene, and fluoranthene were examined. Within the naphthalene catabolic pathway, no enzymes have been assigned to the ring-opening of 1,2-dihydroxynaphthalene or the hydration and retro-aldol cleavage of trans-o-hydroxybenzylidenepyruvate. Within the phenanthrene catabolic pathway, 1-hydroxy-2-naphtoate and trans-o-carboxybenzylidenepyruvate are thought to be processed by the enzymes designated PhdI and PhdJ, respectively. The results show that PhdI ring-opens 1-hydroxy-2-naphthoate but not 1,2-dihydroxynaphthalene. The hydratase-aldolase PhdJ processes both trans-o-hydroxybenzylidenepyruvate and trans-o-carboxybenzylidenepyruvate but prefers trans-o-carboxybenzylidenepyruvate. Ring-opening of both 3,4-dihydroxyphenanthrene and 9,10-dihydroxyphenanthrene, intermediates in the phenanthrene catabolic pathway, have previously been assigned to PhdF. However, the results show that PhdF catalyzes the ring-opening of 3,4-dihydroxyphenanthrene but not 9,10-dihydroxyphenanthrene. We also show that the product of the PhdF-catalyzed reaction using 3,4-dihydroxyphenanthrene is processed by PhdG, the enzyme proposed to do this reaction. Finally, PhdF was reported to catalyze all ring-opening reactions in the upper catabolic pathways for pyrene and fluoranthene. We find that PhdF does not catalyze any of these proposed reactions in the pyrene pathway and investigations in the fluoranthene pathway are ongoing. The sum of our observations clarifies the reaction pathways for the degradation of naphthalene, phenanthrene, pyrene, and fluoranthene in M. vanbaalenii PYR-1. This work sets the stage for detailed mechanistic studies of the individual enzymes. This knowledge, combined with the considerable body of literature on PAH degradation pathways, could guide the development and optimization of bioremediation technologies.