Distribution of Dibenzofuran-Degrading Bacteria in Soils Polluted with Different Levels of Polychlorinated Dioxins

Abstract

Aerobic chemoorganotrophic bacteria in soils polluted with different levels of polychlorinated dioxins (6.8 to 4,600 pg-TEQ g-1 dry weight) were isolated by the quantitative agar-plating method and tested for their ability to degrade dibenzofuran (DF) using DF-overlaid agar and DF-containing liquid media. For comparison, bacteria isolated from river sediments were also tested. Out of the 5,069 strains thus isolated, 23 strains were found to be able to degrade DF, and the majority produced soluble yellow metabolites during the degradation. A higher isolation frequency for DF degraders was obtained with samples containing higher concentrations of polychlorinated dioxins. Most of the DF-degrading isolates were identified as members of the class Actinobacteria, particularly of the genera Nocardioides and Rhodococcus. These results suggest that particular actinobacterial species constitute the major populations of culturable DF-degrading bacteria in dioxin-polluted environments.