Characterization and genetic analyses of a carbazole-degrading gram-positive marine isolate, Janibacter sp. strain OC11

The potential application of carbazole-degrading bacteria for dioxin bioremediation

Extensive research has been conducted over the years on the bacterial degradation of dioxins and their related compounds including carbazole, because these chemicals are highly toxic and has been widely distributed in the environment. There is a pressing need to explore and develop more bacterial strains with unique catabolic features to effectively remediate dioxin-polluted sites. Carbazole has a chemical structure similar to dioxins, and the degradation pathways of these two chemicals are highly homologous. Some carbazole-degrading bacterial strains have been demonstrated to have the ability to degrade dioxins, such as Pseudomonas sp. strain CA10 và Sphingomonas sp. KA1. The introduction of strain KA1 into dioxin-contaminated model soil resulted in the degradation of 96% and 70% of 2-chlorodibenzo-p-dioxin (2-CDD) and 2,3-dichlorodibenzo-p-dioxin (2,3-DCDD), respectively, after 7-day incubation period. These degradation rates were similar to those achieved with strain CA10, which removed 96% of 2-CDD and 80% of 2,3-DCDD from the same model soil. Therefore, carbazole-degrading bacteria hold significant promise as potential candidates for dioxin bioremediation. This paper overviews the connection between the bacterial degradation of dioxins and carbazole, highlighting the potential for dioxin biodegradation by carbazole-degrading bacterial strains.

Purification and partial characterization of the extradiol dioxygenase, 2′-carboxy-2,3-dihydroxybiphenyl 1,2-dioxygenase, in the fluorene degradation pathway from Rhodococcus sp. strain DFA3

Type II extradiol dioxygenase, 2′-carboxy-2,3-dihydroxybiphenyl 1,2-dioxygenase (FlnD1D2) involved in the fluorene degradation pathway of Rhodococcus sp. DFA3 was purified to homogeneity from a heterologously expressing Escherichia coli. Gel filtration chromatography and SDS-PAGE suggested that FlnD1D2 is an α4β4 heterooctamer and that the molecular masses of these subunits are 30 and 9.9 kDa, respectively. The optimum pH and temperature for enzyme activity were 8.0 and 30 °C, respectively. Assessment of metal ion effects suggested that exogenously supplied Fe2+ increases enzyme activity 3.2-fold. FlnD1D2 catalyzed meta-cleavage of 2′-carboxy-2,3-dihydroxybiphenyl homologous compounds, but not single-ring catecholic compounds. The Km and kcat/Km values of FlnD1D2 for 2,3-dihidroxybiphenyl were 97.2 μM and 1.5 × 10−2 μM−1sec−1, and for 2,2′,3-trihydroxybiphenyl, they were 168.0 μM and 0.5 × 10−2 μM−1sec−1, respectively. A phylogenetic tree of the large and small subunits of type II extradiol dioxygenases suggested that FlnD1D2 constitutes a novel subgroup among heterooligomeric type II extradiol dioxygenases.