Polycyclic aromatic hydrocarbon metabolism by white rot fungi and oxidation by Coriolopsis gallica UAMH 8260 laccase

We studied the metabolism of polycyclic aromatic hydrocarbons (PAHs) by usi ng white rot fungi previously identified as organisms that metabolize polyc hlorinated biphenyls. Bran flakes medium, which has been shown to support p roduction of high levels of laccase and manganese peroxidase, was used as t he growth medium. Ten fungi grown for 5 days in this medium in the presence of anthracene, pyrene, or phenanthrene, each at a concentration of 5 mu g/ ml could metabolize these PAHs, We studied the oxidation of 10 PAHs by usin g laccase purified from Coriolopsis gallica, The reaction mixtures containe d 20 mu M PAH, 15% acetonitrile in 60 mM phosphate buffer (pH 6), 1 mM 2,2' -azinobis-(3-ethylbenzthiazoline-6-sulfonate) (ABTS), and 5 U of laccase, L accase exhibited 91% of its maximum activity in the absence of acetonitrile . The following seven PAHs were oxidized by laccase: benzo[a]pyrene, 9-meth ylanthracene, 2-methylanthracene, anthracene, biphenylene, acenaphthene, an d phenanthrene. There was no clear relationship between the ionization pote ntial of the substrate and the first-order rate constant (k) for substrate loss in vitro in the presence of ABTS, The effects of mediating substrates were examined further by using anthracene as the substrate. Hydroxybenzotri azole (HBT) (1 mM) supported approximately one-half the anthracene oxidatio n rate (k = 2.4 h(-1)) that ABTS (1 mM) supported (k = 5.2 h(-1)), but 1 mM HBT plus 1 mM ABTS increased the oxidation rate ninefold compared with the oxidation rate in the presence of ABTS, to 45 h(-1). Laccase purified from Pleurotus ostreatus had an activity similar to that of C. gallica laccase with HBT alone, with ABTS alone, and with 1 mM HBT plus 1 mM ABTS, Mass spe ctra of products obtained from oxidation of anthracene and acenaphthene rev ealed that the dione derivatives of these compounds were present.