Isolation and characterization of pure cultures for metabolizing 1,4-dioxane in oligotrophic environments

1,4-Dioxane concentration in most contaminated water is much less than 1 mg/L, which cannot sustain the growth of most reported 1,4-dioxane-metabolizing pure cultures. These pure cultures were isolated following enrichment of mixed cultures at high concentrations (20 to 1,000 mg/L). This study is based on a different strategy: 1,4-dioxane-metabolizing mixed cultures were enriched by periodically spiking 1,4-dioxane at low concentrations (≤1 mg/L). Five 1,4-dioxane-metabolizing pure strains LCD6B, LCD6D, WC10G, WCD6H, and WD4H were isolated and characterized. The partial 16S rRNA gene sequencing showed that the five bacterial strains were related to Dokdonella sp. (98.3%), Acinetobacter sp. (99.0%), Afipia sp. (99.2%), Nitrobacter sp. (97.9%), and Pseudonocardia sp. (99.4%), respectively. Nitrobacter sp. WCD6H is the first reported 1,4-dioxane-metabolizing bacterium in the genus of Nitrobacter. The net specific growth rates of these five cultures are consistently higher than those reported in the literature at 1,4-dioxane concentrations <0.5 mg/L. Compared to the literature, our newly discovered strains have lower half-maximum-rate concentrations (1.8 to 8.2 mg-dioxane/L), lower maximum specific 1,4-dioxane utilization rates (0.24 to 0.47 mg-dioxane/(mg-protein ⋅ d)), higher biomass yields (0.29 to 0.38 mg-protein/mg-dioxane), and lower decay coefficients (0.01 to 0.02 d^-1). These are characteristics of microorganisms living in oligotrophic environments.