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

Abstract

ABSTRACTThe bacteriumPseudonocardia dioxanivoransCB1190 grows on the cyclic ethers 1,4-dioxane (dioxane) and tetrahydrofuran (THF) as sole carbon and energy sources. Prior transcriptional studies indicated that an annotated THF monooxygenase (THF MO) gene cluster,thmADBC, located on a plasmid in CB1190 is upregulated during growth on dioxane. In this work, transcriptional analysis demonstrates that upregulation ofthmADBCoccurs during growth on the dioxane metabolite β-hydroxyethoxyacetic acid (HEAA) and on THF. Comparison of the transcriptomes of CB1190 grown on THF and succinate (an intermediate of THF degradation) permitted the identification of other genes involved in THF metabolism. Dioxane and THF oxidation activity of the THF MO was verified inRhodococcus jostiiRHA1 cells heterologously expressing the CB1190thmADBCgene cluster. Interestingly, thesethmADBCexpression clones accumulated HEAA as a dead-end product of dioxane transformation, indicating that despite its genes being transcriptionally upregulated during growth on HEAA, the THF MO enzyme is not responsible for degradation of HEAA in CB1190. Similar activities were also observed in RHA1 cells heterologously expressing thethmADBCgene cluster fromPseudonocardia tetrahydrofuranoxydansK1.