POTENTIAL OF LACCASE PRODUCED FROM MICROFUNGUS, AUREOBASIDIUM PULLULANS VAR. MELANOGENUM, TO DEGRADE POLY-AROMATIC HYDROCARBONS

Abstract

Poly-aromatic hydrocarbons (PAHs) are a group of persistent organic pollutants that are resistant to degradation and can remain in the environment for a long time. PAHs are mainly produced as by-products of incomplete combustion, such as from fossil fuel burning, forest fires, coal fires or vehicle emissions. Currently, PAHs increasingly cause major environmental problems because of continuing industrial development. Biodegradation by microbes is the major natural mechanism for PAHs removal from the environment. The main objective of this research was to study the biodegradation of four types of PAHs (naphthalene, anthracene, pyrene and benzo[a]pyrene) by laccase produced from the lipolytic yeast, Aureobasidium pullulans var. melanogenum , screened from Sichang Island (Thailand). The optimal condition for growing A. pullulans var. melanogenum and its laccase production was first evaluated, and revealed that laccase production could be induced with 2 mM guaiacol and 0.5 M CuSO 4 in the yeast malt (YM) growth medium. Laccase was then lyophilized and stored in capsule form at +4oC to maintain enzymatic activity. The subsequent ability to degrade naphthalene, anthracene, pyrene and benzo[a]pyrenewas determined using high performance liquid chromatography. The results revealed that the laccase activity of one capsule (0.16 g) of lyophilized laccase was 711 U mL -1 (4.4 U mg -1 ) and could degrade a mixture of benzo[a]pyrene (37 µg mL -1 ), anthracene (7.5 µg mL -1 ), pyrene (99 µg mL -1 ) and naphthalene (90 µg mL -1 ) by 45.33, 38.16, 25.38 and 24.35% after 48 hours incubation respectively. Furthermore, the result also revealed that laccase (5 g) from A. pullulans can degrade naphthalene and anthracene in soil samples by 51.34 and 85.06% respectively, after incubation for 9 days.