ROLE OF A LACCASE IN THE DEGRADATION OF PENTACHLOROPHENOL

White rot fungi, which are capable of degrading lignin present in wood , are able to degrade many structurally diverse organic pollutants. Th e organism often used as a model is Phanerochaete chrysosporium, altho ugh the ability of Trametes (Coriolus) versicolor to degrade xenobioti c chemicals has also been investigated. The ability to mineralize orga nic pollutants in vitro is generally enhanced under culture conditions favorable to the mineralization of the lignin model compounds which s uggests that the lignin-degrading system may be involved in the transf ormation of anthropogenic compounds (Bumpus and Aust 1986). Fungal ext racellular enzymes, including lignin peroxidases (LiPs) and laccases, are implicated in the degradation of lignin. Researchers have proposed that the LiPs of P. chrysosporium are key enzymes in the fungal degra dation of xenobiotic compounds (Kirk and Shimada 1985). Sanglard et al . (1986) demonstrated that LiPs catalyzed the initial oxidation of ben zo(a)pyrene [B(a)P] by this fungus. Hammel et al. (1992) suggested tha t anthraquinone, produced in an LiP-catalyzed reaction, was an interme diate in the mineralization of anthracene by P. chrysosporium. Both la ccases and lignin peroxidases act via a nonspecific free radical mecha nism, are secreted extracellularly, and are implicated in lignin degra dation. Although LiPs have been considered as catalysts in the mineral ization of xenobiotic compounds by white rot fungi, the laccases have not. The oxidation of many o-and p-diphenols and of some m-diphenols a nd monophenols is catalyzed by laccases (Bendall and Gregory 1963). An isolated laccase of T. versicolor oxidized PCP, producing the benzoqu inones, p-chloranil and o-chloranil (Konishi and Inoue 1972). Although the purified laccases and lignin peroxidases oxidize a variety of che micals, it remains uncertain whether they are integral catalysts in th e mineralization pathways of xenobiotics by white rot fungi. An attemp t was made in the present investigation to clarify the role of laccase in the transformation of PCP during growth of a fungus, T. versicolor . The temporal relationship between the mineralization of C-14-PCP and the formation of extracellular laccase by the fungus was determined. The ability of an isolated extracellular laccase to increase the rate of PCP mineralization by T. versicolor was assessed. Finally, products resulting from the transformation of PCP by the fungal cultures and b y the isolated laccase were characterized and compared.