Preliminary examinations for applying a carbazole-degrader, Pseudomonas spstrain CA10, to dioxin-contaminated soil remediation

A method for bioremediation of chlorinated dibenzo-p-dioxins (CDDs) and dib enzofurans (CDFs) by a carbazole-utilizing bacterium. Pseudomonas sp. strai n CA10. was developed. CA10 cells transferred to carbon-and nitrogen-free m ineral medium supplemented with I mg carbazole (CAR)/ml grew rapidly during the first 2 days, and the cells at the end of this rapid growth period sho wed the highest 2,3-dichlorodibenzo-p-dioxin (2,3-Cl2DD)-degrading activity . The CA10 cells pregrown for 2 days efficiently degraded 2,3-Cl2DD in aque ous solution at either 1 ppm or 10 ppm. The effect of inoculum density on t he efficiency of 2,3-Cl2DD degradation was investigated in a soil slurry mi crocosm [ratio of soil:water = 1:5 (w/v)]. The results showed that a single inoculation with CA10 cells at densities of 10(7) CFU/g soil and 10(9) CFU /g soil degraded 46% and 80%, of 2.3-Cl2DD, respectively, during the 7-day incubation. The rate of degradation of each CDD congener, 2-ClDD, 2,3-Cl2DD , and 1,2,3-Cl3DD (1 ppm each) by strain CA10 in the soil slurry system was not significantly influenced by the coexistence of the other congeners. Us ing this soil slurry system, we tried an experimental bioremediation of the actual dioxin-contaminated soil. which contained mainly tetra- to octochlo rinated dioxins. Although the degradation rate of total CDD and CDF congene rs by a single inoculation with CA10 cells was 8.3% after a 7-day incubatio n. It was shown that strain CA10 had a potential to degrade tetra- to hepta -chlorinated congeners including the most toxic compound, 2,3,7,8-tetrachlo rinated dibenzo-p-dioxin.