The metabolism of biphenyl, naphthalene, anthracene, phenanthrene, pyrene and benzo[a]pyrene by Cyclothyrium sp. CBS 109850, a coelomycete isolated for the first time in Brazil from industrially polluted estuarine sediment, was studied. The metabolites were extracted and separated by high performance liquid chromatography (HPLC) and characterized by UV spectral analyses and mass, and proton nuclear magnetic resonance (H-1 NMR) spectrometry. Cyclothyrium sp. transformed biphenyl to 4-hydroxybiphenyl and anthracene to anthracene trans-1,2-dihydrodiol. This isolate metabolized 90% of [9-C-14] phenanthrene, producing phenanthrene trans-9,10-dihydrodiol as a major metabolite, phenanthrene trans-3,4-dihydrodiol, 1-hydroxyphenanthrene, 3-hydroxyphenanthrene, 4-hydroxyphenanthrene, and a novel metabolite, 2-hydroxy-7-methoxyphenanthrene. Circular dichroism spectra analyses indicated that the major enantiomers of phenanthrene trans-9, 10-dihydrodiol, phenanthrene trans-3,4-dihydrodiol and pyrene trans-4,5-dihydrodiol, a pyrene metabolite produced previously by Cyclothyrium sp. CBS 109850, were predominantly in the (R,R) configuration, revealing a high stereoselectivity for initial monooxygenation and enzymatic hydration of phenanthrene and pyrene by Cyclothyrium sp. CBS109850. The results also show a high regioselectivity since the K-regions of phenanthrene and pyrene were the major sites of metabolism. (C) 2004 Elsevier Ltd. All rights reserved.578943952