Abstract
Benzo[a]pyrene is considered as a priority pollutant because of its carcinogenic, teratogenic and mutagenic effects. The highly recalcitrant nature of Benzo[a]pyrene poses a major problem for its degradation. White-rot fungi such as Pleurotus ostreatus can degrade Benzo[a]pyrene by enzymes like laccase and manganese peroxidase. The present investigation was carried out to determine the extent of Benzo[a]pyrene degradation by the PO-3, a native isolate of P. ostreatus, in the presence of heavy metals and ligninolytic enzyme mediators. Modified mineral salt medium was supplemented with 5 mM concentration of different heavy metal salts and ethylenediaminetetraacetic acid. Vanillin and 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (1 and 5 mM) were used to study the effect of mediators. Results indicated that P. ostreatus PO-3 degraded 71.2 % of Benzo[a]pyrene in the presence of copper ions. Moderate degradation was observed in the presence of zinc and manganese. Both biomass formation and degradation were severely affected in the presence of all other heavy metal salts used in the study. Copper at 15 mM concentration supported the best degradation (74.2 %), beyond which the degradation progressively reduced. Among the mediators, 1 mM 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonate) supported 78.7 % degradation and 83.6 % degradation was observed under the influence of 5 mM vanillin. Thus, metal ion like copper is essential for better biodegradation of Benzo[a]pyrene. Compared to synthetic laccase mediator like 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonate), natural mediator such as vanillin may play a significant role in the degradation of aromatic compounds by white-rot fungi.
Highlights
Benzo[a]pyrene (BaP), a representative of high molecular weight polycyclic aromatic hydrocarbon (HMW PAH), consists of five fused benzene rings and is of environmental concern since it behaves as a potent teratogen, mutagen and carcinogen
P. ostreatus is a whiterot basidiomycete fungus whose ligninolytic enzyme machinery consists of laccase and manganese peroxidase
The results showed varied levels of BaP degradation in the presence of heavy metals
Summary
Benzo[a]pyrene (BaP), a representative of high molecular weight polycyclic aromatic hydrocarbon (HMW PAH), consists of five fused benzene rings and is of environmental concern since it behaves as a potent teratogen, mutagen and carcinogen. Different strategies for removal of BaP and other highly recalcitrant compounds from contaminated sites include chemical oxidation, photolysis and biodegradation. Among all these clean up strategies, involvement of microorganisms is a subject of intense research and gains a cutting. Bacteria are capable of degrading the low molecular weight PAH, such as naphthalene, acenaphthene and phenanthrene and relatively few genera have been observed to degrade the HMW PAHs, such as BaP (Juhasz and Naidu 2000). Several white-rot fungi (Phanerochaete chrysosporium, Coriolus versicolor, Stropharia coronilla, Pleurotus ostreatus, Irpex lacteus and Bjerkandera adusta) that synthesizes extracellular lignin modifying enzymes like lignin peroxidases (LiP), manganese peroxidases (MnP), laccases and other oxidases can oxidize BaP and similar HMW PAHs with up to six aromatic rings (Pointing 2001)
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