Cometabolic Biodegradation of 1,4-Dioxane and Co-occurring Chlorinated Aliphatic Hydrocarbons by Psychrophilic Propanotrophs Enriched with a New Cluster of Group-6 Soluble Di-iron Monooxygenases

Commingled contamination of 1,4-dioxane (dioxane) and chlorinated aliphatic hydrocarbons (CAHs) is prevalent in groundwater at impacted sites. Here, we enriched and characterized two psychrophilic consortia that can degrade dioxane and a wide spectrum of CAHs (e.g., trichloroethene, 1,1-dichloroethene, 1,2-cis-dichloroethene, and vinyl chloride) under an aquifer-relevant temperature (14 °C) when fed with propane. Functional gene-targeted sequencing revealed the dominance (>70%) of group-6 soluble di-iron monooxygenases (SDIMOs) in both consortia, crucial for concurrent propane consumption and co-oxidation of dioxane and CAHs. Sequence data mining and phylogenetic analysis uncovered three distinct clusters (I, II, and III) within group-6 SDIMOs, with the most abundant SDIMO (48-59%) in cluster III, sharing partial sequence identity with the α subunit of a group-6 SDIMO in a propanotroph Mycobacterium sp. ENV421. Sequence comparison highlighted the divergence of group-6 cluster-III SDIMOs, exhibiting amino acid features (e.g., proline avoidance and glycine substitution) in proximity of the active sites that can be relevant to their psychrophilicity, emphasizing the necessity to characterize their catalytic behaviors and develop sensitive biomarkers for field assessment. This research sheds light on the unique adaptations of psychrophilic consortia and their potential for remediation strategies in cold groundwater environments with a commingled contamination of dioxane and CAHs.