Biodegradation of benzo(a)pyrene by fungi

Abstract

Biodegradation of Benzo(a)pyrene (BaP) by fungi which isolated from leaves and barks of Pterocarpus macrocarpus Kurz. long exposed to the heavy traffic smoke. Fifty three fungi were obtained in total. The fungi isolated from leaves could be classified as 40 epiphytic fungi and 7 endophytic fungi, while 6 fungal isolates were obtained from barks. These fungal isolates were tested for their ability to degrade 100 ppm. BaP (0.4 mM) on solid medium. There were 13 fungal isolates which have the positive response towards BaP. These isolates were then tested in liquid medium in order to investigate BaP biodegradation ability. Three fungal isolates were finally obtained having relatively high BaP degradation ability when grown on glucose- containing medium supplemented with 100 ppm. BaP (0.4 mM) at 32°c, with 120 rpm- shaking conditions. These three fungal isolates were identified morphologically and genetically to be Aspergillus niger N003, Aspergillus niger B002 and Fusariu moxysporum E033. Then, for each three isolates, BaP degradation kinetics, factors affecting the biodegradation as well as the biodegradation intermediates formed during the biodegradation process were investigated. A sp erg illu s n ig er N003, Aspergillus niger B002 and Fusariu m oxysporum E033 exhibited 80%, 70% and 65% BaP biodegradation efficiency, respectively. To all fungal isolates, when the aeration rate was increased, the fungal biomass was increased as well as their biodegradation. Higher concentrations of BaP (up to 300 ppm) become toxic to cells; however, they maintained to have BaP biodegradability, although with less efficiency. Higher glucose concentration (50 mM) promoted fungal biomass, but the biodegradation was significantly repressed. Ethanol or methanol was supplemented as an alternative carbon source and to enhance BaP bioavailability in liquid medium. They were successfully increased fungal biomass, but had adverse effect to BaP biodegradation. The intermediates from BaP biodegradation of each fungal isolate were revealed using liquid chromatography and mass spectrometry. Aspergillus niger N003 and Aspergillus niger B002 biotransformed BaP to dihydroxy-dihydrodiol, whereas Fusarium oxysporum E033 biotransformed BaP via 2 different pathways forming different biodegradation intermediates. While the extra-cellular BaP biodegradation by Fusarium oxysporum E033 yielded BaP quinone, BaP dihydrodiol and BaP diol epoxide were detected via intra-cellular BaP biodegradation.