Although remaining a focus of continued research, early evidence indicates that compound specific isotope analysis (CSIA) can be a useful monitoring tool when assessing aerobic biodegradation of the emerging contaminant 1,4-dioxane.
- Aerobic Metabolism: An increasing number of microorganisms have been isolated that utilize dioxane as a growth supporting substrate under aerobic conditions suggesting biodegradation is a viable attenuation mechanism. Recently, the Mahendra lab reported a carbon isotope enrichment factor of -1.73‰ during the aerobic metabolism of dioxane by Pseudonocardia dioxanivorans CB1190 (Pornwongthong et al. 2011).
- Aerobic Cometabolism: Under aerobic conditions, dioxane is also amenable to cometabolism by several groups of organisms expressing monooxygenase genes for the metabolism of a variety of primary substrates including methane, propane and other n-alkanes, tetrahydrofuran, and toluene (Lan et al. 2013; Mahendra and Alvarez-Cohen 2006; Masuda et al. 2012; Vainberg et al. 2006).
To date, carbon isotope enrichment factors have not been reported for aerobic cometabolism of dioxane. However, like aerobic metabolism of dioxane, cometabolic degradation is initiated by monooxygenases. Moreover, the same major intermediate was identified during cometabolic dioxane degradation as observed in dioxane metabolism by CB1190 (Mahendra et al. 2007). While an enrichment factor has not yet been reported in the literature, the similarity of pathways for aerobic metabolism and cometabolism at least suggests that carbon isotope fractionation may be observed during cometabolic degradation of dioxane as was reported for dioxane metabolism.
Also Consider Stable Isotope Probing: Stable isotope probing (SIP) is an innovative method to track the environmental fate of a 13C “labeled” contaminant like benzene to conclusively determine if biodegradation is occurring. The 13C label serves much like a tracer. If biodegradation is occurring the 13C label will be detected in the end products of biodegradation – biomass and dissolved inorganic carbon (CO2). CSIA on the other hand is based on analysis of the 13C/12C ratio of the contaminant itself.
Also Consider CENSUS qPCR: CSIA can be performed in conjunction with qPCR to quantify functional genes involved in the aerobic metabolism and cometabolism of dioxane. In aerobic dioxane utilizing bacteria including Pseudonocardia dioxanivorans CB1190, the first step in dioxane metabolism is mediated by a dioxane monooxygenase (DXMO) and a key downstream step is mediated by an aldehyde dehydrogenase enzyme (ALDH). Therefore, qPCR assays have been developed to quantify the DXMO and ALDH genes to evaluate the potential for dioxane metabolism in environmental samples (Gedalanga et al. 2014). Microbial Insights also offers qPCR assays to quantify functional genes encoding enzymes capable of dioxane cometabolism including soluble methane monooxygenase (sMMO), propane monooxygenase (PPO) and aromatic monooxygenases (RMO, RDEG, PHE).
Gedalanga, P.B., P. Pornwongthong, R. Mora, S.-Y.D. Chiang, B. Baldwin, D. Ogles, and S. Mahendra. 2014. Identification of Biomarker Genes To Predict Biodegradation of 1,4-Dioxane. Applied and Environmental Microbiology 80 no. 10: 3209-3218.
Lan, R.S., C.A. Smith, and M.R. Hyman. 2013. Oxidation of Cyclic Ethers by Alkane-Grown Mycobacterium vaccae JOB5. Remediation Journal 23 no. 4: 23-42.
Mahendra, S., and L. Alvarez-Cohen. 2006. Kinetics of 1,4-Dioxane Biodegradation by Monooxygenase-Expressing Bacteria. Environmental Science & Technology 40 no. 17: 5435-5442.
Mahendra, S., C.J. Petzold, E.E. Baidoo, J.D. Keasling, and L. Alvarez-Cohen. 2007. Identification of the Intermediates of in Vivo Oxidation of 1,4-Dioxane by Monooxygenase-Containing Bacteria. Environmental Science & Technology 41 no. 21: 7330-7336.
Masuda, H., K. McClay, R.J. Steffan, and G.J. Zylstra. 2012. Biodegradation of Tetrahydrofuran and 1,4-Dioxane by Soluble Diiron Monooxygenase in <b><i>Pseudonocardia</i></b> sp. Strain ENV478. Journal of Molecular Microbiology and Biotechnology 22 no. 5: 312-316.
Pornwongthong, P., G.L. Paradis, and S. Mahendra. 2011. Stable Carbon Isotope Fractionation During 1,4-Dioxane Biodegradation. Proceedings of the Water Environment Federation 2011 no. 18: 111-116.
Vainberg, S., K. McClay, H. Masuda, D. Root, C. Condee, G.J. Zylstra, and R.J. Steffan. 2006. Biodegradation of Ether Pollutants by Pseudonocardia sp. Strain ENV478. Applied and Environmental Microbiology 72 no. 8: 5218-5224.