The Abundance of Tetrahydrofuran/Dioxane Monooxygenase Genes (thmA/dxmA) and 1,4-Dioxane Degradation Activity Are Significantly Correlated at Various Impacted Aquifers

Abstract

1,4-Dioxane (dioxane) is a cocontaminant of emerging concern at thousands of sites impacted by chlorinated solvents, and there is an urgent need to assess site-specific dioxane biodegradation capabilities. In this study, a primer/probe set was developed to target bacterial genes encoding the large hydroxylase subunit of a putative tetrahydrofuran/dioxane monooxygenase (an enzyme proposed to initiate dioxane catabolism), using TaqMan (5′-nuclease) chemistry. This effort relied on multiple-sequence alignment of the four thmA/dxmA genes available on the National Center for Biotechnology Information database. The probe targets conserved regions surrounding the active site, thus allowing detection of multiple dioxane degraders. Real-time polymerase chain reaction using reference strain genomic DNA demonstrated the high selectivity (no false positives) and sensitivity of this probe (7000–8000 copies/g of soil). Microcosm tests prepared with groundwater samples from 16 monitoring wells at five different dioxane-impacted sites showed that enrichment of this catabolic gene (up to 114-fold) was significantly correlated with the amount of dioxane degraded. A significant correlation was also found between biodegradation rates and the abundance of thmA/dxmA genes. In contrast, 16S rRNA gene copy numbers (a measure of total bacteria) were neither sensitive nor reliable indicators of dioxane biodegradation activity. Overall, these results suggest that this novel catabolic biomarker (thmA/dxmA) has great potential for the rapid assessment of the performance of natural attenuation or bioremediation of dioxane plumes.