1. Approximately 98% of dibenzothiophene (DBT) was converted to DBT su
lphoxide (86% of total metabolites) and DBT sulphone (14% of total met
abolites) after a 24-h incubation with the filamentous fungus Cunningh
amella elegans (ATCC-36112). 2. DBT sulphoxidation was significantly d
ecreased in incubations with the concomitant additions of metyrapone,
piperonyl butoxide and 1-aminobenzotriazole indicating a P450 monooxyg
enase-catalysed reaction. 3. DBT sulphoxidation was also significantly
decreased by methimazole, but only slightly decreased with a thiourea
addition, suggesting a possible role of a flavin-containing, monooxyg
enase-catalysed activity. 4. The extracellular filtrate of C. elegans
failed to show measurable DBT oxidation, showing that biotransformatio
n is intracellular and is not catalysed by an extracellular process.