Anaerobic 1,4-dioxane biodegradation and microbial community analysis in microcosms using various electron acceptorss

1,4-dioxane, a probable human carcinogen, is a co-contaminant at many chlorinated solvent contaminated sites. Although numerous 1,4-dioxane degrading aerobic bacteria have been isolated, almost no information exists on the microorganisms able to degrade this chemical under anaerobic conditions. Here, the potential for 1,4-dioxane biodegradation was examined using multiple inocula and electron acceptor amendments. The inocula included uncontaminated agricultural soils and river sediments as well as sediments from two 1,4-dioxane contaminated sites. Compound specific isotope analysis (CSIA) was used to further investigate biodegradation in a subset of the microcosms. Also, DNA was extracted from microcosms exhibiting 1,4-dioxane biodegradation for microbial community analysis using 16S rRNA gene amplicon high throughput sequencing.Given the long incubation periods, it is likely that electron acceptor depletion occurred and methanogenic conditions eventually dominated. The iron/EDTA/humic acid or sulfate amendments did not result in 1,4-dioxane biodegradation in the majority of cases. 1,4-dioxane biodegradation was most commonly observed in the nitrate amended and no electron acceptor treatments. Notably, both contaminated site sediments illustrated removal in the samples compared to the abiotic controls in the no electron acceptor treatment. However, it is important to note that the degradation was slow (with concentration reductions occurring over approximately one year). In two of the three cases examined, CSIA provided additional evidence for 1,4-dioxane biodegradation. In one case, the reduction in 1,4-dioxane in the samples compared the controls was likely too low for the method to detect a significant 13C/12C enrichment. Further research is required to determine the value of measuring 2H/1H for generating evidence for the biodegradation of this chemical.The microbial community analysis indicated the phylotypes unclassified Comamonadaceae and 3 genus incertae sedis were more abundant in 1,4-dioxane degrading microcosms compared to the live controls (no 1,4-dioxane) in microcosms inoculated with contaminated and uncontaminated sediment, respectively. The relative abundance of known 1,4-dioxane degraders was also investigated at the genus level. The soil microcosms were dominated primarily by Rhodanobacter with lower relative abundance values for Pseudomonas, Mycobacterium and Acinetobacter. The sediment communities were dominated by Pseudomonas and Rhodanobacter. Overall, the current study indicates 1,4-dioxane biodegradation under anaerobic, and likely methanogenic conditions, is feasible. Therefore, natural attenuation may be an appropriate clean-up technology at sites where time is not a limitation.