Metabolism of hydroxydibenzofurans, methoxydibenzofurans, acetoxydibenzofurans, and nitrodibenzofurans by Sphingomonas sp. strain HH69

Abstract

The metabolism of 11 substituted dibenzofurans by the dibenzofuran- degrading Sphingomonas sp. strain HH69 was investigated. Strain HH69 utilizes 2-, 3-, and 4-acetoxydibenzofuran as well as 2-, 3-, and 4- hydroxydibenzofuran as sole sources of carbon and energy. The degradation of acetoxydibenzofurans is initiated by hydrolysis of the ester bonds, yielding the corresponding hydroxydibenzofurans and acetate. Strain HH69 grew on 2- methoxydibenzofuran only after it was adapted to the utilization of 5- methoxysalicylic acid, whereas 3- and 4-methoxydibenzofuran as well as 2- and 3-nitrodibenzofuran were only cooxidized. During the breakdown of all eight hydroxy-, methoxy-, and nitrodibenzofurans studied here, the corresponding substituted salicylic acids accumulated in the culture broth. In the cases of 2- and 3-hydroxydibenzofuran as well as 2- and 3-nitrodibenzofuran, salicylic acid was also formed. Those four dibenzofurans which did not serve as carbon sources for strain HH69 were converted to a nonutilizable salicylic acid derivative. From turnover experiments with the mutant HH69/II, which is deficient in meta-cleavage, 2,2',3,4'-tetrahydroxybiphenyl, 2,2',3- trihydroxy-5'-methoxybiphenyl, 2,2',3-trihydroxy-5'-nitrobiphenyl, and 2,2',3-trihydroxy-4'-nitrobiphenyl were isolated as the main products formed from 3-hydroxydibenzofuran, 2-methoxydibenzofuran, and 2- and 3- nitrodibenzofuran, respectively. These results indicate significant regioselectivity for the dioxygenolytic cleavage of the ether bond of these monosubstituted dibenzofurans, with a preference for the nonsubstituted aromatic nucleus. Substituted trihydroxybiphenyls are converted further by meta-cleavage followed by the removal of the side chain of the resulting product. A stepwise degradation of this side chain was found to be involved in the metabolism of 2-hydroxydibenzofuran.