DEGRADATION OF FLUORENE BY BREVIBACTERIUM SP STRAIN DPO-1361 - A NOVEL C-C BOND-CLEAVAGE MECHANISM VIA 1,10-DIHYDRO-1,10-DIHYDROXYFLUOREN-9-ONE

Angular dioxygenation has been established as the crucial step in dibe nzofuran degradation by Brevibacterium sp. strain DPO 1361 (V. Strubel , K.H. Engesser, P. Fischer, and H.-J. Knackmuss, J. Bacteriol. 173:19 32-1937, 1991). The same strain utilizes biphenyl and fluorene as sole sources of carbon and energy. The fluorene degradation sequence is pr oposed to be initiated by oxidation of the fluorene methylene group to 9-fluorenol. Cells grown on fluorene exhibit pronounced 9-fluorenol d ehydrogenase activity. Angular dioxygenation of the 9-fluorenone thus formed yields 1,10-dihydro-1,10-dihydroxyfluoren-9-one (DDF). A mechan istic model is presented for the subsequent C-C bond cleavage by an NA D(+)-dependent DDF dehydrogenase, acting on the angular dihydrodiol. T his enzyme was purified and characterized as a tetramer of four identi cal 40-kDa subunits. The following K-m values were determined: 13 mu M for DDF and 65 mu M for 2,3-dihydro-2,3-dihydroxybiphenyl. The enzyme also catalyzes the production of 3-(2'-carboxyphenyl)catechol, which was isolated, and structurally characterized, in the form of the corre sponding lactone, 4-hydroxydibenzo-(b,d)-pyran-6-one. Stoichiometry an alysis unequivocally demonstrates that angular dioxygenation constitut es the principal pathway in Brevibacterium sp. strain DPO 1361.