Theme: 14. Emerging Contaminants

Topic Area: 14b. Advances in 1,4-Dioxane Biological Treatment Technologies

Formatted Title:

Phylogenetic and Functional Gene Analysis during 1,4-Dioxane Biodegradation in Soil, Wetland and Sediment Samples

Background/Objectives:

1,4-Dioxane is a probable human carcinogen, was commonly used as a stabilizer in 1,1,1-trichloroethane formulations and is now frequently detected at sites where the chlorinated solvents are present. A major challenge in addressing 1,4-dioxane contamination concerns chemical characteristics that result in migration and persistence.

Given the limitations associated with traditional remediation methods, interest has turned to bioremediation to address 1,4-dioxane contamination. Although many isolates capable of 1,4-dioxane biodegradation have been characterized, less is known about the microorganisms responsible for biodegradation in mixed community samples. In this study, the impact of yeast extract additions on 1,4-dioxane biodegradation rates was examined in three mixed microbial community samples. Further, the microorganisms responsible for uptake from 1,4-dioxane were identified and the functional genes associated with contaminant biodegradation were investigated.

Approach/Activities:

For each treatment, triplicate laboratory microcosms were inoculated with agricultural soil, wetland soil and sediment from an impacted site. 1,4-Dioxane concentrations were monitored over time using a triple quadrupole GC/MS system (Agilent 7010B) equipped for solid phase microextraction. Extracted DNA was subject to stable isotope probing (SIP), involving ultracentrifugation, fractionation and 16S rRNA gene sequencing (Illumina). The ultracentrifugation fractions were subject to amplicon sequencing to investigate the functional genes associated with 1,4-dioxane biodegradation. Additionally, the 16S rRNA gene sequencing data were subject to a predictive approach to determine the phylotypes associated with propane monooxygenase, soluble methane monooxygenase, toluene monooxygenases and ammonia monooxygenase.

Results/Lessons Learned:

1,4-Dioxane removal rates were positively impacted by the presence of the additional amendments. Biodegradation rates varied between the three microbial communities. Limited removal was noted in the abiotic controls. The SIP analysis indicated different phylotypes were responsible for the uptake of carbon in each set of samples. In the wetland samples, Gemmatimonas, Alphaproteobacteria, Massilia and Rhizobiales were enriched in the heavy SIP fractions compared to the light SIP fractions. In the soil communities, RB4, Udaeobacter, Solirubrobacter and Pseudonocardia were dominant in the SIP heavy fractions. In the impacted sediments, Burkholderiaceae, OC32 and Gemmatimonas were enriched in the heavy fractions. Interestingly, a group of phylotypes were both enriched in the heavy fractions and were also predicted to be associated with one or more monooxygenases. For example, Pseudonocardia and Solirubrobacter were both associated with propane monooxygenases and Burkholderiaceae was associated with toluene monooxygenase. The results of the functional gene amplicon sequencing is still ongoing.

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Zheng Li