PARENT SESSION
TA5 Biodegradation and biotransformation: routes and pathways
9:00 AM to 12:30 PM, Tuesday, 08 May 2001
Session Chair: K. Solomon
Room 5

(182) Degradation of polycylicaromatic hydrocarbons by a pyrene-degrading baterium.

Grifoll, Magdalena¹, Vila, Joaquim¹, López, Zaira¹, Sabaté, Jordi¹, Solanas, Anna¹, Minguillón, Cristina¹, ¹

ABSTRACT- Strain AP1, a Gram-positive aerobic rod currently being identified, is able to utilize pyrene as a sole source of carbon and energy. Pyrene assimilation into cell biomass was estimated to be approximately 10%. Washed-cell incubations of strain AP1 accumulated five major metabolites from pyrene. Four of these metabolites were identified (HPLC, GC-MS) as 4,5-dihydropyrene-4,5-diol (4,5-PyrDHD), 4,5-phenanthrenedicarboxylic acid (4,5-PheDCA), 4-phenanthrenecarboxylic acid (4-PheCA) and phthalic acid (PhA). In addition to those metabolites a previously undescribed metabolite resulting from double ring cleavage was identified as 6,6'-dihydroxy-2,2'-biphenyldicarboxylic acid (6,6'-DH-2,2'-BphDCA) by NMR techniques. The accumulated products suggest a branched metabolic pathway for the oxidation of pyrene by strain AP1. This pathway involves dioxygenation on positions C-4, C-5 to give 4,5-PyrDHD, which after dehydrogenation and intradiolic cleavage yields 4,5-PheDCA. A decarboxylation of the latter product would produce 4-PheCA, which by further ring-cleavages initiated in the carboxylated ring would lead to PhA formation. An alternative degradative pathway includes dioxygenation on C-4, C-5 and C-9, C-10 positions and cleavage of both oxygenated rings to give the novel metabolite 6,6'-DH-2,2'-BphDCA. The salient features of this pathway are: i) an ortho cleavage of the central aromatic ring, atypical in the initial steps of PAHs degradation, ii) C1 loss by aryl decarboxylation, and iii) consecutive cleavage of the central aromatic rings to give the novel biphenyl derivative. Strain AP1 is also able to use phenanthrene, fluoranthene and the alkane hexadecane for growth, and transforms acenaphthene, dibenzothiophene, fluorene, and napththalene. Some of the actions of the strain in those compounds include monooxygenation of benzylic methylenic groups, sulfoxidation, and ortho cleavage of naphthalene and phenanthrene to give the uncommon metabolites 2-carboxycinnamic acid and 2,2'-biphenyldicarboxylic acid, repectively. These and other reactions and their effects on the degradation of PAH mixtures are discussed.

Key words: polycyclic aromatic hydrocarbons, biodegradation, pyrene, biotransformation