Bioremediation potential of soil contaminated with highly substituted polychlorinated dibenzo-p-dioxins and dibenzofurans: Microcosm study and microbial community analysis

Highly chlorinated dibenzo-p-dioxins/dibenzofurans (DD/Fs) are main hazardous dioxins, and ubiquitously distributed in the environment. To study the feasibility of bioremediation for remedying contamination of highly chlorinated dioxins, closed microcosms were constructed with soil from a chronological site under oxygen-stimulated conditions. The results showed that high levels of near-fully and fully chlorinated DD/Fs, particularly octachlorodibenzofuran were effectually reduced without accumulation of less substituted congeners. The clone library analysis of PCR-amplified 16S rRNA gene from the octachlorodibenzofuran-degrading consortia showed that 98.3% of the detected sequences were affiliated with Proteobacteria. The obtained strains with putative aromatic dioxygenase genes and abilities to repetitively grow in octachlorodibenzofuran-containing agars were closely related to members within Actinobacteria, Firmicutes, and Proteobacteria. Among them, certain Rhodococcus, Micrococcus, Mesorhizobium and Bacillus isolates could degrade octachlorodibenzofuran with efficiencies of 26-43% within 21 days. Hierarchical oligonucleotide primer extension analysis further showed that Micrococcus, Rhizobium, Pseudoxanthomonas, and Brevudimonas populations increased largely when high concentrations of octachlorodibenzofuran were reduced. Overall, our results suggest that a distinctive microbial composition and population dynamic could be required for the enhanced degradation of highly chlorinated DD/Fs in the batch microcosm and highlight a potential of bioremediation technologies in remedying polychlorinated dioxins in the polluted sites.