Pathway, inhibition and regulation of methyl tertiary butyl ether oxidation in a filamentous fungus, Graphium sp.
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The filamentous fungus Graphium sp. (ATCC 58400) co-metabolically oxidizes the gasoline oxygenate methyl tertiary butyl ether (MTBE) after growth on gaseous n-alkanes. In this study, the enzymology and regulation of MTBE oxidation by propane-grown mycelia of Graphium sp. were further investigated and defined. The trends observed during MTBE oxidation closely resembled those described for propane-grown cells of the bacterium Mycobacterium vaccae JOB5. Propane-grown mycelia initially oxidized the majority (∼95%) of MTBE to tertiary butyl formate (TBF), and this ester was biotically hydrolyzed to tertiary butyl alcohol (TBA). However, unlike M. vaccae JOB5, our results collectively suggest that propane-grown mycelia only have a limited capacity to degrade TBA. None of the products of MTBE exerted a physiologically relevant regulatory effect on the rate of MTBE or propane oxidation, and no significant effect of TBA was observed on the rate of TBF hydrolysis. Together, these results suggest that the regulatory effects of MTBE oxidation intermediates proposed for MTBE-degrading organisms such as Mycobacterium austroafricanum are not universally relevant mechanisms for MTBE-degrading organisms. The results of this study are discussed in terms of their impact on our understanding of the diversity of aerobic MTBE-degrading organisms and pathways and enzymes involved in these processes.
KeywordsMethyl tertiary butyl alcohol Cometabolism Graphium sp. Tertiary butyl alcohol Tertiary butyl formate Alkane monooxygenase
The authors thank Mohammed Azizian for technical assistance. This research was supported by a graduate fellowship through the US Environmental Protection Agency’s Science to Achieve Results (STAR) graduate fellowship program awarded to K.M.S. This research was supported in part by a research grant from the US Environmental Protection Agency-sponsored Western Region Hazardous Substance Research Center under agreement R-828772. This work was partially supported through an award to A.M.P. through Consejo Nacional de Ciencia y Tecnología (CONACyT). This article has not been reviewed by the agencies, and no official endorsement should be inferred.
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