Metabolism and Cometabolism of Cyclic Ethers by a Filamentous Fungus, aGraphiumsp

Abstract

The filamentous fungus Graphium sp. (ATCC 58400) grows on gaseous n-alkanes and diethyl ether. nAlkane-grown mycelia of this strain also cometabolically oxidize the gasoline oxygenate methyl tert-butyl ether (MTBE). In this study, we characterized the ability of this fungus to metabolize and cometabolize a range of cyclic ethers, including tetrahydrofuran (THF) and 1,4-dioxane (14D). This strain grew on THF and other cyclic ethers, including tetrahydropyran and hexamethylene oxide. However, more vigorous growth was consistently observed on the lactones and terminal diols potentially derived from these ethers. Unlike the case in all previous studies of microbial THF oxidation, a metabolite, ␥-butyrolactone, was observed during growth of this fungus on THF. Growth on THF was inhibited by the same n-alkenes and n-alkynes that inhibit growth of this fungus on n-alkanes, while growth on ␥-butyrolactone or succinate was unaffected by these inhibitors. Propane and THF also behaved as mutually competitive substrates, and propane-grown mycelia immediately oxidized THF, without a lag phase. Mycelia grown on propane or THF exhibited comparable high levels of hemiacetal-oxidizing activity that generated methyl formate from mixtures of formaldehyde and methanol. Collectively, these observations suggest that THF and n-alkanes may initially be oxidized by the same monooxygenase and that further transformation of THF-derived metabolites involves the activity of one or more alcohol dehydrogenases. Both propane-and THF-grown mycelia also slowly cometabolically oxidized 14D, although unlike THF oxidation, this reaction was not sustainable. Specific rates of THF, 14D, and MTBE degradation were very similar in THF-and propane-grown mycelia.

Glyoxylate Metabolism Is a Key Feature of the Metabolic Degradation of 1,4-Dioxane by Pseudonocardia dioxanivorans Strain CB1190

“…Recently, the pathways of dioxane biotransformation have been studied in a number of metabolizing and cometabolizing bacteria and fungi in an attempt to understand the fate of environmentally released dioxane. A common feature of dioxane transformation is the initial hydroxylation of the dioxane ring by monooxygenase enzyme systems (23,41,48), which is similar to the findings of the toxicological studies. The hydroxylated metabolite then undergoes uncharacterized biotic or abiotic processing, leading to an opening of the ring structure.…”

“…Consequently, dioxane contamination has become the focus of remediation research, and microbial systems capable of dioxane degradation have been investigated (56). The degradation of dioxane under cometabolic conditions (where other substrates provide carbon and energy for growth) appears to be somewhat common (9,23,27,41,43,48), but an increasing number of microorganisms have also been identified that can use dioxane as a sole source of carbon and energy (5,15,23,27,30).…”

“…Consequently, dioxane contamination has become the focus of remediation research, and microbial systems capable of dioxane degradation have been investigated (56). The degradation of dioxane under cometabolic conditions (where other substrates provide carbon and energy for growth) appears to be somewhat common (9,23,27,41,43,48), but an increasing number of microorganisms have also been identified that can use dioxane as a sole source of carbon and energy (5,15,23,27,30).Initial investigations of biological dioxane transformation were performed as part of toxicological studies, which identified hydroxyethoxyacetic acid (HEAA) and 1,4-dioxane-2-one as the major metabolites in humans (55) and rats (52), respectively. Recently, the pathways of dioxane biotransformation have been studied in a number of metabolizing and cometabolizing bacteria and fungi in an attempt to understand the fate of environmentally released dioxane.…”

Oxidation of the Cyclic Ethers 1,4-Dioxane and Tetrahydrofuran by a Monooxygenase in Two Pseudonocardia Species

“…A number of pure and mixed cultures of bacteria and fungi have been reported to degrade dioxane aerobically (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12), while only one study has reported anaerobic degradation (13). To date, nine microorganisms have been reported to be capable of growth on dioxane as a sole carbon and energy source (i.e., metabolism of dioxane), including Rhodococcus ruber 219 (1), Mycobacterium sp.…”

“…In the fungus Graphium sp. ATCC 58400, a cytochrome P450 MO enzyme was suggested to catalyze the initial oxidation of THF (7).…”