Ligninolytic enzymes production during polycyclic aromatic hydrocarbons degradation: effect of soil pH, soil amendments and fungal co-cultivation.

Soil microorganisms play an important role in the degradation of PAHs and use various metabolic pathways for this process. The effect of soil pH, different soil amendments and the co-cultivation of fungi on the degradation of PAHs in soil and on the activity of ligninolytic enzymes was evaluated. For that purpose, three fungi were studied: Trichoderma viride, Penicillium chrysogenum and Agrocybe aegerita. Biodegradation assays with a mixture of 200 ppm PAHs (fluorene, pyrene, chrysene, and benzo[a]pyrene-50 ppm each) were set up at room temperature for 8 weeks. The maximum laccase activity by solid state fermentation-SSF (7.43 U/g) was obtained by A. aegerita on kiwi peels with 2 weeks and the highest manganese peroxidase activity (7.21 U/g) was reached in 4 weeks, both at pH 7. Fluorene, pyrene, and benzo[a]pyrene achieved higher degradation rates in soil at pH 5, while chrysene was more degradable at pH 7. About 85-90% of the PAHs were degraded by fungal remediation. The highest degradation of fluorene was achieved by co-cultivation of A. aegerita and P. chrysogenum, remaining 14% undegradable. Around 13% of pyrene stay undegradable by A. aegerita and T. viride and by A. aegerita and P. chrysogenum, both systems supported in kiwi peels, while 11% of chrysene remained in soil by the co-cultivation of these fungi, supported by peanut shells. Regarding benzo[a]pyrene, 13% remained in soil after treatment with A. aegerita. Despite the increase in degradation of some PAHs with co-cultivation, higher enzyme production during degradation was observed when fungi were cultivated alone.