Factors affecting the degradation of polyaromatic hydrocarbons in soil by white-rot fungi

In tests it was found that white-rot (lignin-degrading) fungi (WRF) growing in soil did not degrade significant amounts of polyaromatic hydrocarbons (PAHs), although they did degrade some other organopollutants. However, in liquid culture they degraded many PAHs. Experiments using 14C-labelled benzo(a)pyrene [14C(B(a)P)] as a representative PAH were carried out in both liquid and soil culture to determine what factors might limit the PAH-degrading activity of WRF in the soil. Trametes (Coriolus) versicolor (L.:Fr.) Pilat was used as the test WRF. In liquid culture, the fungus formed a range of unidentified polar metabolites from the 14C B(a)P. 14CO2 production (mineralization) was significant, but low. Addition of soil, sawdust or ground alfalfa (substances present in the tests that had been carried out in the soil) inhibited formation of the polar metabolites, but had little effect on mineralization. In contrast, addition of nitrogen sources had little effect on formation of polar metabolites, but inhibited mineralization. When the radiolabelled polar metabolites were added to soil, they were mineralized much more rapidly by the soil microbial community than 14C B(a)P. Degradation of 14C B(a)P by WRF in liquid medium was faster by fungi that had been exposed to PAHs, suggesting that the degradative system was inducible. Degradation in soil was increased by some surfactants, these increasing the B(a)P concentration in the soil moisture. The increased degradation may have been due to increased accessibility of the B(a)P to the degradative system, or to induction of the WRF degradative system.