Mycoremediation of polluting substances by basidiomycetes.

Mycoremediation is a form of bioremediation that uses fungal mycelia to return an environment contaminated by pollutants to a less contaminated state. One of the primary role of fungi in the ecosystem is decomposition which is performed by the mycelium. White-rot fungi secrete extracellular enzymes and acids that breakdown lignin and cellulose, the two main building blocks of plant fiber. The ligninolytic enzymes have low substrate specificity and that permits them the degradation of organic xenobiotic compounds with different origin, scarcely susceptible to bacterial attack. The key to mycoremediation is determining the right fungal species to target a specific pollutant. In IBAF laboratories a fungal germplasm bank is present (International Bank of Edible Saprophytic Mushrooms), containing about 530 samples of wood-degrading fungi, mainly Pleurotus. Fungi belonging to Pleurotus genus have been used for the treatment of polluted waste for many years. In particular, olive mill waste waters were used as growth medium for P. ostreatus, with the result of an abundant mycelium growth and the decrease of COD and phenols in the waste waters. P. ostreatus was able to grow in a mixture containing wood treated with creosote (CTW) and wheat straw, totally degrading phenols and reducing the 65-70% of polycyclic aromatic hydrocarbons and heterocyclic compounds. To clarify the degradation of polyciclic aromatic hydrocarbons (PAH), a study was performed in batch on fluoranthene, one of the principal PAH contained in creosote. The results pointed out that this compound was totally absorbed by the mycelium (15 days) and then degraded by 50% in 40 days. Also the antibiotic Oxytetracycline, that enters the environmental compartments as a consequence of animal waste disposal, disappeared in P. ostreatus culture medium as early as the third day of exposure onwards, with an almost complete removal after 14 days.