Degradation of chlorinated dibenzofurans and dibenzo-p-dioxins by two types of bacteria having angular dioxygenases with different features

Abstract

Two kinds of bacteria having different-structured angular dioxygenases-a dibenzofuran (DF)-utilizing bacterium, Terrabacter sp. strain DBF63, and a carbazole (CAR)-utilizing bacterium, Pseudomonas sp. strain CA10-were investigated for their ability to degrade some chlorinated dibenzofurans (CDFs) and chlorinated dibenzo-p-dioxins (CDDs) (or, together, CDF/Ds) using either wild-type strains or recombinant Escherichia coli strains. First, it was shown that CAR 1,9a-dioxygenase (CARDO) catalyzed angular dioxygenation of all mono- to triCDF/Ds investigated in this study, but DF 4,4a-dioxygenase (DFDO) did not degrade 2,7-diCDD. Secondly, degradation of CDF/Ds by the sets of three enzymes (angular dioxygenase, extradiol dioxygenase, and meta-cleavage compound hydrolase) was examined, showing that these enzymes in both strains were able to convert 2-CDF to 5-chlorosalicylic acid but not other tested substrates to the corresponding chlorosalicylic acid (CSA) or chlorocatechol (CC). Finally, we tested the potential of both wild-type strains for cooxidation of CDF/Ds and demonstrated that both strains degraded 2-CDF, 2-CDD, and 2,3-diCDD to the corresponding CSA and CC. We investigated the sites for the attack of angular dioxygenases in each CDF/D congener, suggesting the possibility that the angular dioxygenation of 2-CDF, 2-CDD, 2,3-diCDD, and 1,2,3-triCDD (10 ppm each) by both DFDO and CARDO occurred mainly on the nonsubstituted aromatic nuclei.

FIG. 1

Conversion of DD and DF by DFDO from Terrabacter sp. strain DBF63 and by CARDO from Pseudomonas sp. strain CA10.

FIG. 2

Proposed initial dioxygenolytic attack on the tested CDFs and CDDs by DFDO and CARDO. Panel 1, 2-CDF, 5′-chloro-2,2′,3-THB (reaction A) and 5-chloro-2,2′,3-THB (reaction B); panel 2, 2,8-DCDF, 5,5′-dichloro-2,2′,3-THB (reaction A); panel 3, 2-CDD, 5′-chloro-2,2′,3-THDE (reaction A), 4′-chloro-2,2′,3-THDE (reaction A′), 5-chloro-2,2′,3-THDE (reaction B), and 4-chloro-2,2′,3-THDE (reaction B′); panel 4, 2,3-DCDD, 4′,5′-dichloro-2,2′,3-THDE (reaction A) and 4,5-dichloro-2,2′,3-THDE (reaction B); panel 5, 2,7-DCDD, 4,5′-dichloro-2,2′,3-THDE (reaction A) and 4′,5-dichloro-2,2′,3-THDE (reaction B); panel 6, 1,2,3-TCDD, 4′,5′,6′-trichloro-2,2′,3-THDE (reaction A), 3′,4′,5′-trichloro-2,2′,3-THDE (reaction A′), and 4,5,6-trichloro-2,2′,3-THDE (reaction B). Possible sites attacked by angular dioxygenases are indicated by A or A′ on the nonsubstituted rings and by B or B′ on the halogen-substituted rings, with the exception of those in panels 2 and 5. ND, not detected.