Structural and molecular genetic analyses of the bacterial carbazole degradation system

Carbazole degradation by several bacterial strains, including Pseudomonas resinovorans CA10, has been investigated over the last two decades. As the initial reaction in degradation pathways, carbazole is commonly oxygenated at angular (C9a) and adjacent (C1) carbons as two hydroxyl groups in a cis configuration. This type of dioxygenation is termed "angular dioxygenation," and is catalyzed by carbazole 1,9a-dioxygenase (CARDO), consisting of terminal oxygenase, ferredoxin, and ferredoxin reductase components. The crystal structures of all components and the electron transfer complex between terminal oxygenase and ferredoxin indicate substrate recognition mechanisms suitable for angular dioxygenation and specific electron transfer among the three components. In contrast, the carbazole degradative car operon of CA10 is located on IncP-7 conjugative plasmid pCAR1. Together with conventional molecular genetic and biochemical investigations, recent genome sequencing and RNA mapping studies have clarified that transcriptional cross-regulation via nucleoid-associated proteins is established between pCAR1 and the host chromosome.