A Novel Propane Monooxygenase Initiating Degradation of 1,4-Dioxane by Mycobacterium dioxanotrophicus PH-06

Monitored natural attenuation and bioremediation are cost-efficient and eco-friendly approaches to mitigating prevalent 1,4-dioxane (dioxane) plumes. Unfortunately, their field applications have been greatly undermined given our scarce knowledge of the diversity of dioxane biodegradation pathways and associated key enzymes. At present, only tetrahydrofuran monooxygenases (THF MOs) are known to initiate dioxane degradation in dioxane metabolizers. In this study, we deciphered the essential catalytic role of a novel propane MO (encoded by the prmABCD gene cluster) in dioxane metabolism by Mycobacterium dioxanotrophicus PH-06. This propane MO is phylogenetically distinct from THF MOs on the basis of the low levels of amino acid sequence identity (<40% for α subunits). Reverse transcription polymerase chain reaction (RT-PCR) analysis revealed that the prmABCD gene cluster is an intact transcription unit that can be induced by dioxane, THF, or propane. In addition, the biotransformation activity of this propane MO toward dioxane, THF, and propane was confirmed using heterologous expression. Detection of 2-hydroxyethoxyacetic acid (HEAA) in the expression clones proves that this propane MO catalyzes dioxane decomposition via α-hydroxylation. This first enzymological identification of the propane MO in PH-06 expands our understanding of dioxane metabolic pathways and unequivocally enables the development of molecular tools for improving the assessment of natural attenuation and bioremediation at dioxane-impacted sites.