Distinct Catalytic Behaviors between Two 1,4-Dioxane-Degrading Monooxygenases: Kinetics, Inhibition, and Substrate Range

Abstract

Monitored natural attenuation (MNA) and engineered bioremediation have been recognized as effective and cost-efficient in situ treatments to mitigate 1,4-dioxane (dioxane) contamination. Dioxane metabolism can be initiated by two catabolic enzymes, propane monooxygenase (PRM) and tetrahydrofuran monooxygenase (THM), belonging to the group-6 and 5 of soluble di-iron monooxygenase family, respectively. In this study, we comprehensively compared catalytic behaviors of PRM and THM when individually expressed in the heterologous host, Mycobacterium smegmatis mc 2 -155. Kinetic results revealed a half-saturation coefficient (K m ) of 53.0 ± 13.1 mg/L for PRM, nearly 4 times lower than that of THM (235.8 ± 61.6 mg/L), suggesting that PRM has a higher affinity to dioxane. Exposure with three common co-contaminants (1,1dichloroethene, trichloroethene, and 1,1,1-trichloroethane) demonstrated that PRM was also more resistant to their inhibition than THM. Thus, dioxane degraders expressing PRM may be more physiologically and ecologically advantageous than those with THM at impacted sites, where dioxane concentration is relatively low (e.g., 250 to 1000 μg/L) with co-occurrence of chlorinated solvents (e.g., 0.5 to 8 mg/L), underscoring the need of surveying both PRM and THM-encoding genes for MNA potential assessment. PRM is also highly versatile, which breaks down cyclic molecules (dioxane, tetrahydrofuran, and cyclohexane), as well as chlorinated and aromatic pollutants, including vinyl chloride, 1,2-dichloroethane, benzene, and toluene. This is the first report regarding the ability of PRM to degrade a variety of short-chain alkanes and ethene in addition to dioxane, unraveling its pivotal role in aerobic biostimulation that utilizes propane, isobutane, or other gaseous alkanes/alkenes (e.g., ethane, butane, and ethene) to select and fuel indigenous microorganisms to tackle the commingled contamination of dioxane and chlorinated compounds.

Acetylene Tunes Microbial Growth During Aerobic Cometabolism of Trichloroethene

“…The continued propane consumption in both cultures after acetylene exposure may be attributed to expression of multiple types of oxygenases, such as copper membrane monooxygenases (CuMMOs), particulate methane membrane-bound monooxygenases (pMMOs), particulate hydrocarbon monooxygenases (pHMOs), soluble cytoplasmic methane monooxygenases (sMMOs), short-chain alkane monooxygenases (SCAM), or soluble di-iron monooxygenases (SDIMOs) . Studies show that the rate of TCE cometabolism mediated by sMMOs and CuMMOs is much higher than by the pMMO counterpart. − pHMO, SCAM, and SDIMO are not considered the primary enzymes responsible for TCE oxidation. ,, Therefore, if expressed, pHMO, SCAM, and SDIMO would have only been involved in the biodegradation of propane.…”

Characterization of 1,4-Dioxane Biodegradation by a Microbial Community

“…The biodegradation potential of 1,4-dioxane was evaluated in different natural bacteria sources, indicating that 1,4-dioxane degrading bacteria are not ubiquitously distributed in natural environment; an interesting conclusion of this study was that 1,4-dioxane degrading bacteria do not always exist in contaminated sources [28]. These studies have demonstrated the existence of 1,4-dioxane degrading bacteria; however, to date, the kinetics of biodegradation by a mixed culture in the sole carbon source of 1,4-dioxane and the effect of extra carbon source on its kinetic coefficients are sparse [29,30].…”

Emerging investigator series: environment-specific auxiliary substrates tailored for effective cometabolic bioremediation of 1,4-dioxane

“…Expression of this TMO appeared inducible by both propane and its primary oxidation product, 1-propanol, implying their potential as auxiliary substrates for cometabolic bioremediation. 30 Furthermore, unlike the majority of dioxane degrading actinomycetes, 31 DD4 has the tmo gene on its chromosome. 29 This is important as it precludes the loss of the essential dioxane degradation genes when the culture is fed with liquid alcohols and other non-selective substrates that are readily biodegradable.…”