Comparative biotransformation of pentachlorophenol in soils by solid substrate cultures of Lentinula edodes

Sterilised and non-sterilised soils contaminated with pentachlorophenol (PCP) were inoculated with solid substrate cultures of Lentinula edodes LE2 ("shiitake" mushroom) to simulate monoculture bioremediation treatments and treatments in which the fungus competes with natural microflora. With monocultures of L. edodes, rates of PCP depletion were rapid for the initial 4 weeks and, although thereafter the rate decreased, 99% biotransformation was obtained in 10 weeks. In mixed culture, PCP biotransformation by L. edodes was markedly slower and only 42% of the PCP was depleted after 10 weeks. Maximal rates of PCP transformation, biomass (ergosterol) accumulation and oxidative enzymes (phenol oxidase and manganese-peroxidase) production were observed after 2 weeks of incubation. In monocultures, phenol oxidase activity was 195.5 U g-1 and Mn-peroxidase 138.4 U g-1. In mixed cultures, fungal enzyme activities were markedly lower: 70.33 U g-1 for phenol oxidase and 85.0 g-1 for Mn-peroxidase. Analyses of soil metabolites after 10 weeks revealed that monocultures of L. edodes had eliminated both PCP and pentachloroanisole. Pentachloroanisole, however, was detected in soils with the mixed microflora. Both dechlorination and mineralisation of the xenobiotic compound were effected by L. edodes LE2.