Genes of enzymes involved in the biodegradation of carbazole, dibenzofuran, fluorene, and dibenzo-p-dioxin by bacteria

Abstract

Pseudomonas sp. CA10, which can grow on carbazole (CAR) as the sole source of carbon, nitrogen and energy, was isolated from an activated sludge sample. The metabolic intermediates were detected in the culture broth of strain CA10, and the degradation pathway of CAR by strain CA10 was proposed. The degradation pathway consisted of the initial oxidation of an angular position of CAR, a meta-cleavage pathway of 2′-aminobiphenyl-2,3-diol, and the further degradation of anthranilic acid via ortho-cleavage of catechol. Strain TE1, one of the Tn5-mutants of strain CA10, accumulated cis,cis-muconic acid in the presence of CAR. Nucleotide sequence analysis of the flanking region of the Tn5-insertion site revealed that catBC genes encoding the enzymes involved in cis,cis-muconate metabolism and and catR gene encoding the positive regulator of catBC genes were transcribed divergently in strain CA10, and that Tn5 was inserted into catR gene. A bacterial strain DBF63, which can grow on either dibenzofuran (DBF) or fluorene (FN) as the sole source of carbon and energy, was also isolated from soil in Japan. The metabolic intermediates were detected in the culture broth of strain DBF63 grown on DBF or FN, and the degradation pathways of DBF and FN in strain DBF63 were proposed: DBF was subjected to initial oxygenation, meta-cleavage and hydrolysis into salicylate, and further metabolized. The oxygenation of dibenzo-p-dioxin (DD) in a resting cell reaction using the DBF-grown cells of strain DBF63 was observed. In attempt to clone the genes involved in DBF metabolism, two genes encoding extradiol dioxygenases were isolated from strain DBF63. Nucleotide sequence analysis revealed that one of the genes belonged to catechol 2,3-dioxygenase family and another showed significant homology to the β-subunit of protocatechuate 4,5-dioxygenase in deduced amino acid sequence.