Pyrene is metabolized to bound residues by Penicillium janthinellum SFU403

We have previously shown that the filamentous fungus, Penicillium janthinellum SFU403 (SFU403) oxidizes pyrene to pyrene 1,6- and 1,8-quinones and that the level of pyrenequinones (PQs) subsequently declines suggesting that PQs are not terminal metabolites. The purpose of this study was to determine the fate of PQs in SFU403. First, we compared the fate of 14C-pyrene in SFU403 and a non-pyrene-oxidizing fungus, a Paecilomyces sp.. After 7 days of incubation, more than 80% of the radioactivity was cell-associated in both fungi; however, while 90% of the 14C could be extracted from the Paecilomyces sp. as unmetabolized pyrene, 65-80% of the bound radioactivity remained inextractable from SFU403. Further evidence that pyrene oxidation to PQs was required for irreversible binding was obtained by comparing the extent of 14C bound to SFU403 when it was grown for 21 days under conditions that resulted in differing amounts of 14C-pyrene oxidation. The results showed that approximately 40% of the inextractable products were bound residues derived from pyrene metabolites. The balance (60%) could be attributed to strong sorption of unreacted pyrene. We used electron paramagnetic resonance spectroscopy and oxygen consumption studies to demonstrate that both NADPH and glutathione can reduce PQs by one electron to their corresponding semiquinone anion radicals in vitro. These studies demonstrate that PQs are metabolized by SFU403 to bound residues, possibly via semiquinone intermediates.