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

Abstract

A method for bioremediation of chlorinated dibenzo-p-dioxins (CDDs) and dibenzofurans (CDFs) by a carbazole-utilizing bacterium, Pseudomonas sp. strain CA10, was developed. CA10 cells transferred to carbon- and nitrogen-free mineral medium supplemented with 1 mg carbazole (CAR)/ml grew rapidly during the first 2 days; and the cells at the end of this rapid growth period showed 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 aqueous solution at either 1 ppm or 10 ppm. The effect of inoculum density on the efficiency of 2,3-Cl2DD degradation was investigated in a soil slurry microcosm [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. Using this soil slurry system, we tried an experimental bioremediation of the actual dioxin-contaminated soil, which contained mainly tetra- to octochlorinated dioxins. Although the degradation rate of total CDD and CDF congeners by a single inoculation with CA10 cells was 8.3% after a 7-day incubation, 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-tetrachlorinated dibenzo-p-dioxin.

Biodiversity of Dioxin-Degrading Microorganisms and Potential Utilization in Bioremediation.

“…-1 soil resulted in the degradation of 46% and 80% of 2,3-DCDD, respectively, during 7 days of incubation 63) . In this case, the degradation rates for 2-MCDD, 2,3-DCDD and 1,2,3-TrCDD were not significantly influenced by the coexistence of other congeners.…”

“…Cell suspensions of Pseudomonas pseudoalcaligenes strain POB310 cooxidized a DE analogue, 4-carboxybenzophenone, yielding the corresponding angular diol 36,39) . Biodegradation of CAR, a nitrogen-containing DF analogue, via angular dioxygenation has been intensively studied in Pseudomonas resinovorans strain CA10 62,63,117,129,135,137,142,158,159,194) and some other species of Proteobacteria 53,58,84,106,141,142,165) . The metabolic pathway proposed for CAR in Pseudomonas resinovorans strain CA10 is homologous to the degradation route for DF which is initiated by angular dioxygenase attack.…”

Purification and Characterization of Carbazole 1,9a-Dioxygenase, a Three-Component Dioxygenase System of Pseudomonas resinovorans Strain CA10

“…Compared to other degradative reactions for dioxin, angular dioxygenation is one of the attractive degradative mechanisms, because this reaction and subsequent spontaneous ring cleavage result in the destruction of the planar structure from which the toxicity of dioxin derives (27). In fact, strain CA10 expressing CARDO has been found to have the potential of decontaminating dioxin-contaminated soil (12). Therefore, the CARDO enzyme itself and bacteria with CARDO activity could be important tools in the bioremediation of dioxin contamination.…”

Biodegradation of Dibenzofuran by Janibacter terrae Strain XJ-1

“…Physical and chemical treatment procedures seem to be not feasible in the case of large masses of contaminated soil. Recently, bioremediation methods have become widely accepted as an alternative to physical and chemical methods because they can be applied in situ at a relatively low cost [9,12,22]. There have been no reports on microorganisms using PCDDs and PCDFs as the sole source of carbon and energy for growth.…”