SCREENING OF WHITE-ROT FUNGI FOR THEIR ABILITY TO MINERALIZE POLYCYCLIC AROMATIC-HYDROCARBONS IN SOIL

Soil samples from an agricultural field contaminated with 10 ppm C-14- benz(a)anthracene in glass tubes were brought into contact with cultur es of wood-rotting fungi, precultivated on wheat straw substrate. Fort y-five strains of white-rot fungi and four brown-rot fungi were tested for their ability to colonize the soil and to mineralize C-14-benz(a) anthracene to (CO2)-C-14 within a 20-week incubation time. Twenty-two white-rot fungi and all brown-rot fungi were unable to colonize the so il. Twenty-three strains of white-rot fungi, all belonging to the genu s Pleurotus, colonized the soil. During the experiment the noncolonizi ng fungi and their substrate disintegrated more and more to a nonstruc tured pulp From which water diffused into the soil. The same phenomeno n was observed in the control which contained only straw without fungu s and contaminated soil. In samples with colonizing fungi the substrat e as well as the mycelia in the soil remained visibly unchanged during the entire experiment. Surprisingly, most samples with fungi not colo nizing the soil and the control without fungus liberated between 40 an d 58 % of the applied radioactivity as (CO2)-C-14 whereas the samples with the colonizing fungi respired only 15-25 % as (CO2)-C-14. This wa s 3-5 times more (CO2)-C-14 than that liberated from the control (4.9 %) which contained only contaminated soil without straw and fungus. A similar result was obtained with selected colonizing and noncolonizing fungi and soil contaminated with 10 ppm C-14-pyrene. However, in pure culture studies in which C-14-pyrene was added to the straw substrate , Pleurotus sp. (P2), as a representative of the colonizing fungi, min eralized 40.3 % of the added radioactivity to (CO2)-C-14 The noncoloni zing fungi Dichomitus squalens and Flammulina velutipes liberated only 17.2 or 1.7 %, respectively, as (CO2)-C-14 These results lead to the hypothesis that the native soil microflora stimulated by the formed pr oducts of straw lysis is responsible for high degradation rates found with noncolonizing fungi.