1,4-Dioxane (dioxane) is a groundwater contaminant of emerging concern with human carcinogen potential. Removal of dioxane is usually challenging due to its relative recalcitrance to biodegradation and high migration potential with low tendency to be retarded by sorption. Among different remediation strategies, biodegradation approaches are more economical and environmentally friendly. A number of strains capable of degrading dioxane have been isolated. However, nearly all of these strains were isolated from wastewater treatment plants or dioxane-impacted sites. However, the potential for encountering dioxane degraders in uncontaminated environments, which is important to assess the distribution and potential ubiquity of dioxane degraders and the associated natural attenuation potential, has not been reported in the literature. In my study, two dioxane degrading consortia with similar dioxane degradation rates as archetype degraders were enriched from garden soils with no previous exposure to dioxane. Mycobacterim is the dorminant genus and groups 5 and 6 SDIMOs (soluble diiron monooxygenases) are the genes most likely involved in dioxane degradation. Furthermore, an archetype degraderMycobacterium dioxanotrophicus PH-06 was selected for genetic study because of its higher affinity for dioxane and greater cell yield. Whole genome sequencing of PH-06 identified only one SDIMO gene cluster located in a plasmid. This SDIMO gene cluster has four subunits (a hydroxylase with large and small subunits, a coupling protein, and a reductase) and a total size of approximately 4kb. Because of its high similarity with propane monooxygenase, it was named as prmABCD. RNA-seq and RT-qPCR demonstrated the upregulation ofprmABCD by dioxane. prmABCD is the first identified group-6 SDIMO associated with dioxane degradation. A primer/probe set (prmA) targeting the hydroxylase subunit of prmABCD is very selective and sensitive. The abundance of prmA is significantly correlated with the degradation activity of enriched consortia. These results would broaden the test range of genes involved in dioxane degradation and minimize false negatives. It is important for decisions to accept or reject bioremediation and monitored natural attenuation (MNA) and assess their performances.

Isolation of novel 1,4-dioxane degraders and investigation of responsible catabolic genes

256th National Meeting (2018)

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