Solid state fermentation of olive mill residues by wood- and dung-dwelling Agaricomycetes: effects on peroxidase production, biomass development and phenol phytotoxicity.

The in vivo conversion of dry olive mill residue (DOR) by wood- and dung-dwelling fungi - Auricularia auricula-judae, Bjerkandera adusta and Coprinellus radians - increases peroxidase secretion up to 3.2-3.5-fold (∼1.3, 3.5 and 7.0 Ug(-1) DOR for dye-decolorizing peroxidase, manganese peroxidase and aromatic peroxygenases, respectively). The incubation of DOR with these fungi produced a sharp decrease in total phenolic content (100% within 4 wk), a reduction in phytotoxicity as well as a certain degree of plant growth caused by the stimulating effect of fungal-treated DOR. These findings correlate with a characteristic shift in the fragmentation pattern of water-soluble aromatics (detected at 280 nm) from low (0.2, 1.5 and 2.2 kDa, respectively) to high molecular mass (35 to >200 kDa), which demonstrates the presence of a polymerization process. Phenol-rich agricultural residues are a useful tool for enzyme expression and production studies of peroxidase-producing Agaricomycetes which could make DOR a valuable organic fertilizer.