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

Abstract

The bacterium Pseudonocardia dioxanivorans CB1190 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 of thmADBC occurs during growth on the dioxane metabolite ␤-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 in Rhodococcus jostii RHA1 cells heterologously expressing the CB1190 thmADBC gene cluster. Interestingly, these thmADBC expression 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 the thmADBC gene cluster from Pseudonocardia tetrahydrofuranoxydans K1.

Identification of Biomarker Genes To Predict Biodegradation of 1,4-Dioxane

“…Despite the increased expression after dioxane was removed below the detection limit, our study determined statistically significant inverse relationships between dioxane concentrations and both DXMO and ALDH (Table 3). A number of factors may contribute to the observed expression of DXMO and ALDH in the absence of dioxane, including induction by daughter products of dioxane metabolism as determined in previous studies (29,55). Continued expression upon depletion of inducing substrate has also been shown for reductive dehalogenase-encoding genes.…”

A Multiple Lines of Evidence Framework to Evaluate Intrinsic Biodegradation of 1,4‐Dioxane

“…It should also be noted that 1,4‐dioxane is comingled with THF at this site. THF can serve as a primary substrate for bacteria during cometabolism of 1,4‐dioxane for several microorganisms (Sales et al., ; Sei et al., ; Sun et al., ; Vainberg et al., ). Historical trends indicate that THF and 1,4‐dioxane levels within the plume have decreased concomitantly; though, following the THF plume collapse, decreases in 1,4‐dioxane concentrations at most monitoring locations in the plume since 2013 were more evident (Exhibit ).…”

“…and other environmental isolates (Bernhardt & Diekmann, 1991). Additional studies have linked 1,4-dioxane cometabolism with the presence of a structural analog, tetrahydrofuran (THF) (Masuda et al, 2012;Sales et al, 2013;Sei et al, 2010;Sun et al, 2011). In this situation, 1,4-dioxane biodegradation fortuitously occurs after induction of the necessary enzymes by THF.…”

1,4‐Dioxane‐degrading consortia can be enriched from uncontaminated soils: prevalence of Mycobacterium and soluble di‐iron monooxygenase genes

“…For example, cyclic ethers containing 5‐ and 6‐membered rings are widespread in nature and are used in the biosynthesis of certain antibiotics (Rutkowski and Brzezinski, ; Martín et al ., ), and the capacity to degrade these antibiotics may serve a protective role (Topp et al ., ). Additionally, lactones, which can be intermediates of both dioxane and THF biodegradation (Bernhardt and Diekmann, ; Sales et al ., ) (Fig. S2), are also commonly encountered in nature as chemical signals for bacterial communication (i.e.…”