Toward the bioremediation of dioxin-polluted soil: structural and functional analyses of in situ microbial populations by quinone profiling and culture-dependent methods

In order to obtain basic information toward the bioremediation of dioxin-po lluted soil, microbial communities in farmland soils polluted with high con centrations of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinate d dibenzofurans (PCDFs) were studied by quinone profiling as well as conven tional microbiological methods. The concentration of PCDD/Fs in the pollute d soils ranged from 36 to 4,980 pg toxicity equivalent quality (TEQ) g(-1) dry weight of soil. There was an inverse relationship between the levels of PCDD/Fs and microbial biomass as measured by direct cell counting and quin one profiling. The most abundant quinone type detected was either MK-6 or Q -10. In addition, MK-8, MK-8(H-2), and MK-9(H-8) were detected in significa nt amounts. Numerical analysis of quinone profiles showed that the heavily polluted soils (greater than or equal to1,430 pg TEQ g(-1)) contained diffe rent community structures from lightly polluted soils (less than or equal t o 56 pg TEQ g(-1)). Cultivation of the microbial populations in the heavily polluted soils with dibenzofuran or 2-chlorodibenzofuran resulted in enric hment of Q-10-containing bacteria. When the heavily polluted soil was incub ated in static bottles with autoclaved compost as an organic nutrient addit ive, the concentrations of PCDD/Fs in the soil were decreased by 22% after 3 months of incubation. These results indicate that dioxin pollution exerte d a significant effect on microbial populations in soil in terms of quantit y, quality, and activity. The in situ microbial populations in the dioxin-p olluted soil were suggested to have a potential for the transformation of P CDD/Fs and oxidative degradation of the lower chlorinated ones thus produce d.