Polycyclic Aromatic Hydrocarbon Metabolism by White Rot Fungi and Oxidation by Coriolopsis gallica UAMH 8260 Laccase

Abstract

We studied the metabolism of polycyclic aromatic hydrocarbons (PAHs) by using white rot fungi previously identified as organisms that metabolize polychlorinated biphenyls. Bran flakes medium, which has been shown to support production of high levels of laccase and manganese peroxidase, was used as the 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 μg/ml could metabolize these PAHs. We studied the oxidation of 10 PAHs by using laccase purified from Coriolopsis gallica. The reaction mixtures contained 20 μM 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. Laccase exhibited 91% of its maximum activity in the absence of acetonitrile. The following seven PAHs were oxidized by laccase: benzo[a]pyrene, 9-methylanthracene, 2-methylanthracene, anthracene, biphenylene, acenaphthene, and phenanthrene. There was no clear relationship between the ionization potential 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. Hydroxybenzotriazole (HBT) (1 mM) supported approximately one-half the anthracene oxidation 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 ofC. gallica laccase with HBT alone, with ABTS alone, and with 1 mM HBT plus 1 mM ABTS. Mass spectra of products obtained from oxidation of anthracene and acenaphthene revealed that the dione derivatives of these compounds were present.

Biodegradation of polycyclic aromatic hydrocarbons (PAHs) by Cladosporium sphaerospermum isolated from an aged PAH contaminated soil

“…Thus, a clear correlation between laccase activity and BaP disappearance in fungal cultures was not observed, as reported for the white rot fungus Pleurotus ostreatus [39]. Nevertheless, we cannot exclude the possible role of laccases from C. sphaerospermum, involving an indirect mechanism, as described for white rot fungi [40][41][42]. This metabolic pathway involves the participation of an oxidation mediator -a cooxidant -which could catalyze the initial oxidation of benzo(a)pyrene.…”

Kinetic differences of purified laccases from six Pleurotus ostreatus strains

“…One of the most important aspects of using organic solvents in the reaction medium is the improved solubility of certain substrates. In the case of laccases, the presence of a certain amount of organic solvent is required for the oxidation of hydrophobic substrates such as the polycyclic aromatic hydrocarbons (Pickard et al 1999a). The effect of increasing concentrations of a water-miscible organic solvent (acetonitrile) on syringaldazine oxidation was determined for the different fungal laccases (Fig.…”

“…Laccases catalyse the one-electron oxidation of a wide range of phenolic and aromatic amines (Thurston 1994). The use of laccasemediator systems are promising alternatives for environmental biotechnological processes such as pulp-bleaching (Bourbonnais et al 1995;Li et al 1998), textile dye decolorization (Reyes et al 1999;Rodriguez et al 1999) and oxidation of polycyclic aromatic hydrocarbons (Bohmer et al 1998;Pickard et al 1999a).…”

Biodegradation of high-molecular-weight polycyclic aromatic hydrocarbons by a wood-degrading consortium at low temperatures

“…The lack of specificity and the high oxidant activity of these enzymes make them able to degrade different PAHs (e.g. Pickard et al, 1999). For this reason, Bacillus, Pseudomonas and, in particular, Ralstonia identified within consortium BOS08 and typical of decomposing wood systems have also been previously identified as degraders of aromatic compounds (Zhuang et al, 2002;Chauhan et al, 2008;Luo et al, 2009).…”