Biodegradation of poly-aromatic hydrocarbons by Aureobasidium pullulans var. melanogenum

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 contain two or more fused benzene rings and are mainly produced as byproducts of incomplete combustion, such as from fossil fuel burning, forest fires, coal fires or vehicle emissions. Currently, PAHsincreasingly cause major environmental problems because of continuing industrial development. Biodegradation by microbes is the major natural mechanism for PAH 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, Aureobasidiumpullulans 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 thatlaccaseproduction was induced with 2 mMguaiacoland 0.5 M CuSO₄in the yeast malt (YM)growth medium. Laccase was then lyophilized and stored in capsule form. The subsequent ability to degrade naphthalene, anthracene, pyrene and benzo[a]pyrenewas determinedusing high performance liquid chromatography. The results revealed that the laccase activity of one capsule (0.16 g) of lyophilized laccase was 711 U/mL(4.4 U/mg) and could degrade a mixture of benzo[a]pyrene (37mg/mL), anthracene (7.5mg/mL), pyrene (99 mg/mL) and naphthalene (90 mg/mL) by 45.9, 37.3, 27.3and 24.4% respectively.