Use of the edible mushrooms of the genus Pleurotus and their enzymes for bioremediation of mycotoxin-contaminated commodities.

Mycotoxins are toxic secondary metabolites produced by fungi which contaminate staple food commodities such as grains, fruits, seeds and spices (Logrieco et al., 2002) Mycotoxin contamination is a major and concerning health problem worldwide since they exert toxic effects on humans and animals. In 2012 aflatoxin B1 (AFB1) was classified by the International Agency on Research on Cancer (IARC) as carcinogenic, while aflatoxin M1 (AFM1), fumonisin B1 and Ochratoxin A were enlisted as possible carcinogenic, due to limited data about their toxicity on humans (IARC, 2012). Several approaches have been experimented for the removal of mycotoxins from contaminated agricultural commodities, including biological degradation. The application of microorganisms and enzymes allows to use mild conditions, to avoid the use harmful chemicals and to counteract the loss of the nutritional value or palatability of the decontaminated materials. The microbial degradation of mycotoxins is achived by activity of enzymes able to metabolize, or destroy or deactivate toxins into stable, less toxic, up to harmless compounds. Among fungi, the genus of Pleurotus is known to possess a very efficient ligninolytiuc enzyme system consisting of extracellular oxido-reductase, which have been proven to be involved in mycotoxins degradations (Alberts et al., 2009, Banu et al., 2014; Loi et al., 2016). The aim of this study was to investigate the capability of the edible and cultivated mushroom Pleurotus spp. to degrade AFB1 and identify which enzyme was directly responsible for the degradation. To this purpose, different isolates of P. eryngii were grown on liquid (malt extract broth) agar media (malt extract-agar supplemented with corn flour and wheat, MEASM) and a laboratory-scale mushroom cultivation. All media were supplemented with AFB1. After 30 days of growth at 30 ?1 °C culture media were processed and analyzed for AFB1 by ultra performance liquid chromatography (UPLC/FLD). In the liquid medium all the isolates ompletely removed AFB1 while in the solid medium the degradation ranged from 65 to 84%. In laboratory-scale mushroom cultivation P. eryngii degraded up to 86% of the AFB1, with no significant reduction of either biological efficiency or mushroom yield. In order to evaluate if laccase was truly responsible for mycotoxin degradation, in vitro degradation assays were then performed on AFB1, as well as other mycotoxins, with a purified laccase from P. eryngii. In vitro degradation assays were performed in buffer solution by incubating laccase and the toxin for 72 hours at 25°C. The effect of redox mediators was evaluated as well, by adding to the reaction natural and artificial compounds. A significant reduction of all tested mycotoxins was measured in presence of a redox mediator, with degrading efficacies of 100% for AFM1 and ZEN, of 90% for AFB1 and of 40% for T2 toxin and FB1. These findings make a contribution towards the development of a novel green and effective technology for the bioremediation of mycotoxins contaminated commodities through the exploitation of the degradative capability of P. eryngii due to laccase activity.