Metabolism of Dibenzofuran by Pseudomonas Sp. Strain HH69 and the Mixed Culture HH27

A Pseudomonas sp. strain, HH69, and a mixed culture, designated HH27, were isolated by selective enrichment from soil samples. The pure strain and the mixed culture grew aerobically on dibenzofuran as the sole source of carbon and energy. Degradation proceeded via salicylic acid which was branched into the gentisic acid and the catechol pathway. Both salicylic acid and gentisic acid accumulated in the culture medium of strain HH69. The acids were slowly metabolized after growth ceased. The enzymes responsible for their metabolism showed relatively low activities. Besides the above-mentioned acids, 2-hydroxyacetophenone, benzopyran-4-one (chromone), several 2-substituted chroman-4-ones, and traces of the four isomeric monohydroxydiben-zofurans were identified in the culture medium. 2,2',3-Trihydroxybiphenyl was isolated from the medium of a dibenzofuran-converting mutant derived from parent strain HH69, which can no longer grow on dibenzofuran. This gives evidence for a novel type of dioxygenases responsible for the attack on the biarylether structure of the dibenzofuran molecule. A meta-fission mechanism for cleavage of the dihydroxylated aromatic nucleus of 2,2',3-trihydroxybiphenyl is suggested as the next enzymatic step in the degradative pathway.