In a recent study, researchers from Rice University identified a novel group-6 propane monooxygenase gene cluster (prmABCD) in Mycobacterium dioxanotrophicus PH-06, which is a bacterium with superior dioxane degradation kinetics compared with CB1190. Whole genome sequencing of PH-06 revealed the existence of a single soluble di-iron monooxygenase (SDIMO). RNA sequencing and reverse transcription quantitative PCR (RT-qPCR) subsequently confirmed that all four components of this gene cluster are upregulated when PH-06 is grown on dioxane compared with growth on acetate or glucose as negative controls. This first characterization of a group-6 SDIMO associated with dioxane biodegradation suggests that dioxane-degrading genes may be more diverse than previously appreciated. A primer/probe set designed to target the large hydroxylase subunit of this gene cluster exhibited high selectivity (no false positives) and high sensitivity (detection limit = 3000–4000 gene copies/mL culture), which may be useful to help assess the presence of dioxane degraders at contaminated sites and minimize false negatives.
Neighbor-joining tree showing the phylogenetic relationship of the large hydroxylase subunit of prmABCD with other SDIMOs. The tree was generated on TreeGraph2 based on the alignment of amino acid sequences. Only the strains marked with a red diamond or a blue triangle are confirmed to degrade dioxane metabolically or cometabolically, respectively. The scale bar indicates the average number of amino acid substitutions per site. Group numbers to which these SDIMOs belong to are indicated on the right.