Degradation of polycyclic aromatic hydrocarbons by selected white-rot fungi and the influence of lignin peroxidase

The white-rot fungi Phanerochaete chrysosporium ATCC 24725, Pleurotus ostreatus ATCC 32783, Lentinus edodes ATCC 24462, and Trametes versicolor ATCC 42530 were studied for their ability to degrade lignin, phenanthrene, and anthracene. Lignin in rice-straw was degraded by 14.4, 28.73, and 33.88% by P. chrysosporium, T. versicolor, and P. ostreatus, respectively. Approximately 12% and 83% of phenanthrene was degraded in 1 and 5 days, respectively, when the pre-grown mycellium matrix of P. ostreatus was incubated with 10 ppm of phenanthrene in modified Kirk's medium (nitrogen limited) at 25°C. Approximately 2% and 61% of phenanthrene was degraded when the phenanthrene concentration was increased to 30 ppm. Similar trends were observed with phenanthrene using P. chrysosporium. Mycelial growth of T. versicolor was less inhibited at 30 ppm phenanthrene than for P. ostreatus and P. chrysosporium. Better degradation of phenanthrene by T. versicolor may be attributed to better mycelium growth. One hundred percent of 15 ppm anthracene was degraded in 10 days by both P. chrysosporium and T versicolor. 40 ppm anthracene inhibited the mycelial growth of P. chrysosporium. Lignin peroxidase activity, which was previously reported to be involved in initial phenanthrene oxidation, was also detected from the culture broth of the strains tested. The rates of lignin peroxidase production in the cultures were not consistant with the rate of PAH hydrolysis during incubation.