CENSUS-Dioxane 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. In the aerobic dioxane utilizing microorganism Pseudonocardia dioxanivorans CB1190, the first step in dioxane metabolism is mediated by a dioxane/tetrahydrofuran monooxygenase (DXMO/THFMO). An aldehyde dehydrogenase (ALDH) is co-expressed with DXMO/THFMO.

Therefore, qPCR assays have been developed to quantify the DXMO/THFMO and ALDH genes to evaluate the potential for dioxane/tetrahydrofuran (co)metabolism in environmental samples (Gedalanga et al. 2014).

Target

MI Code 

  Relevance / Data Interpretation

Dioxane/Tetrahydrofuran Monooxygenase
DXMO/THFMO Initiates aerobic metabolism of 1,4-dioxane by

P. dioxanivorans CB1190. In other organisms, DXMO/THFMO initiates metabolism of tetrahydrofuran and co-oxidation of dioxane.

Aldehyde dehydrogenase ALDH Co-expressed with DXMO/THFMO in P. dioxanivornans CB1190.

 

CENSUS – Dioxane 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. To date, cometabolic transformation of dioxane has been observed for monooxygenase-expressing bacteria utilizing propane and other n-alkanes, tetrahydrofuran, and toluene as growth supporting substrates (Lan et al. 2013; Mahendra and Alvarez-Cohen 2006; Masuda et al. 2012; Vainberg et al. 2006). More specifically, the ability to cometabolize dioxane utilizing toluene as a growth supporting substrate appears to be pathway dependent. Bacterial strains expressing toluene-2- and toluene-4-monooxygenases which attack at the ring structure (ring-hydroxylating monooxygenases [RMO and RDEG]) can co-oxidize dioxane. Conversely, organisms initiating toluene metabolism via toluene dioxygenase (TOD) or side chain oxidation (TOL) do not appear to be capable of dioxane cometabolism (Mahendra and Alvarez-Cohen 2006).

The following table describes individual CENSUS targets and their importance in evaluating aerobic cometabolism as a treatment mechanism.

Propane Monooxygenase PPO With addition of propane as a growth supporting substrate, aerobic propane utilizing bacteria are capable of co-oxidation of dioxane.
Ring Hydroxylating Toluene Monooxygenase RMO When expressed, a group of related toluene monooxygenases (RMO, RDEG) that perform the first and/or second step in aerobic biodegradation of BTEX also co-oxidize dioxane. More specifically, RMO quantifies a subfamily of toluene-3- and toluene-4-monooxygenase genes.
Ring Hydroxylating Toluene Monooxygenase RDEG
RDEG targets groups of toluene-2-monoxygenase genes.

Stable Isotope Probing

Stable Isotope Probing (SIP) may also be a viable option for evaluating biodegradation of dioxane in source areas. SIP is an innovative method to track the environmental fate of a “13C-labeled” contaminant of concern such as dioxane to unambiguously demonstrate biodegradation in the field. The label serves as a tracer which can be detected in the end products of biodegradation (biomass and CO2 or dissolved inorganic carbon).

 References

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.

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.

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.