METABOLISM OF HYDROXYDIBENZOFURANS, METHOXYDIBENZOFURANS, ACETOXYDIBENZOFURANS, AND NITRODIBENZOFURANS BY SPHINGOMONAS SP STRAIN HH69

The metabolism of 11 substituted dibenzofurans by the dibenzofuran-deg rading Sphingomonas sp. strain HH69 was investigated. Strain HH69 util izes 2-, 3-, and 4-acetoxydibenzofuran as well as 2-, 3-, and 4-hydrox ydibenzofuran as sole sources of carbon and energy. The degradation of acetoxydibenzofurans ans is initiated by hydrolysis of the ester bond s, yielding the corresponding hydroxydibenzofurans and acetate. Strain HH69 grew on 2-methoxydibenzofuran only after it was adapted to the u tilization of 5-methoxysalicylic acid, whereas 3- and 4-methoxydibenzo furan as well as 2- and 3-nitrodibenzofuran were only cooxidized. Duri ng the breakdown of all eight hydroxy-, methoxy-, and nitrodibenzofura ns studied here, the corresponding substituted salicylic acids accumul ated in the culture broth. In the cases of 2- and 3-hydroxydibenzofura n as well as 2- and 3-nitrodibenzofuran, salicylic acid was also forme d. Those four dibenzofurans which did not serve as carbon sources for strain HH69 were converted to a nonutilizable salicylic acid derivativ e. From turnover experiments with the mutant HH69/II, which is deficie nt in meta-cleavage, 2,2',3,4'-tetrahydroxybiphenyl, 2,2',3-trihydroxy -5'-methoxybiphenyl, 2,2',3-trihydroxy-5'-nitrobiphenyl, and 2,2',3-tr ihydroxy-4'-nitrobiphenyl were isolated as the main products formed fr om 3-hydroxydibenzofuran, 2-methoxydibenzofuran, ind 2- and 3-nitrodib enzofuran, respectively. These results indicate significant regioselec tivity for the dioxygenolytic cleavage of the ether bond of these mono substituted dibenzofurans, with a preference for the nonsubstituted ar omatic nucleus. Substituted trihydroxybiphenyls are converted further by meta-cleavage followed by the removal of the side chain of the resu lting product. A stepwise degradation of this side chain was found to be involved in the metabolism of 2-hydroxydibenzofuran.