Phylogenetical approach to isolation of white-rot fungi capable of degrading polychlorinated dibenzo-p-dioxin

Abstract

A degradation experiment on PCDDs and phylogenetical analyses were carried out on newly isolated 2,7-dichlorodibenzo-p-dioxin (2,7-diCDD)-degrading white-rot fungi, strains BMC3014, BMC9152, and BMC9160. When these fungi were incubated with tri- or tetraCDDs, the substrates were degraded efficiently, and hydroxylated metabolites were detected. On the other hand, 1,3,6,8-tetrachlorodibenzo-p-dioxin was not decreased, and no metabolites were detected. Phylogenetic analysis of internal transcribed spacers (ITSs) containing rRNA gene sequence (ITS-rDNA) clarified that these strains belonged to the genus Phlebia and were closely related to the fungi Phlebia lindtneri, strains MZ-227 and MG-60, which had both been isolated as 2,7-diCDD-degrading fungi in our previous study. Based on this phylogenetical relationship, other Phlebia genera species were used for a degradation experiment on 2,7-diCDD and 1,3,6,8-tetraCDD. Phlebia acerina and Phlebia brevispora degraded 2,7-diCDD about 40 and 80%, respectively, over 14 days of incubation. It became clear that P. brevispora can degrade 1,3,6,8-tetraCDD and transform it to monohydroxy-tetraCDD, monomethoxy-tetraCDD, dimethoxy-tetraCDD, dimethoxy-triCDD, and 3,5-dichlorocatechol in the treatment cultures. In this paper, we could clearly prove for the first time by identifying the metabolites that white-rot fungus P. brevispora could degrade the recalcitrant dioxin, 1,3,6,8-tetraCDD.