Enzymatic mechanisms and detoxification of dry olive-mill residue by Cyclocybe aegerita, Mycetinis alliaceus and Chondrostereum purpureum

Abstract

The detoxification of dry olive-mill residue (DOR), a lignocellulosic by-product, was investigated using three agaric fungi: Cyclocybe aegerita, Mycetinis alliaceus and Chondrostereum purpureum. The lignin-modifying enzymes (LME) secretion pattern of the above-mentioned fungi such as DyP-type peroxidase (DyP), laccase (Lac), unspecific peroxygenase (UPO), and manganese peroxidase (MnP) was determined in presence and absence of DOR. In C. aegerita, a laccase (Lac) and unspecific peroxygenase (UPO) induction was found when DOR was present in the medium. Thus, these enzymes appeared to be responsible for DOR detoxification and, indirectly, its plant-growth-promoting effect. In the experiment performed with M. alliaceus, no differences were found in DyP-type peroxidase (DyP) secretion when the basal barley medium was supplemented with DOR. However, MnP and Lac activities in DOR-barley reached a maximum after 5 weeks of incubation with a concomitant decline in DOR phytotoxicity. C. purpureum completely eliminated DOR phytotoxicity but no significant production of LME was detected in soy or barley fungal media. Other enzymatic mechanisms were also investigated, in relation to hydrolytic enzymes and the intracellular system cytochrome P450 monooxygenase (CYPs). Our results suggest the participation of a complex enzymatic system (intra and extracellular) in C. purpureum for the biotransformation of DOR.