Biodegradation of 1,4-Dioxane by a Novel Strain and Its Biodegradation Pathway

A Gram-negative strain DD1, which could use 1,4-dioxane as the sole carbon and energy source, was isolated from the mixture of activated sludge obtained from Qige urban sewage treatment plant. According to the Biolog GNIII detection and the 16S ribosomal DNA (rDNA) sequence, DD1 was identified as Acinetobacter baumannii. Cells of A. baumannii DD1 precultured in 1,4-dioxane could completely degrade 100 mg/L 1,4-dioxane in 42 h with a cell yield of 0.414 mg-protein (mg-1,4-dioxane)(-1) and a generation time of 6.75 h, demonstrating that DD1 bears the highest 1,4-dioxane-degrading activity among the described strains. Moreover, DD1 tolerates higher 1,4-dioxane concentration almost up to 1,000 mg/L. The strain could also grow on several benzene homologues including benzene, toluene, ethylbenzene, o-xylene, m-xylene, and phenol. During the degradation process of 1,4-dioxane, the first oxidat ion was initiated by monooxygenase in DD1. However, the main second monooxygenation intermediate 2-hydroxyethoxyacetic acid was not detected. As replacer, 1,4-dioxene was identified, and other intermediates such as ethylene glycol and oxalic acid were also detected. Based on the analysis of degradation products, a partial degradation pathway was proposed.