Screening of strains of Lentinula edodes grown on model olive mill wastewater in solid and liquid state culture for polyphenol biodegradation

In Morocco, the olive industry produces great amounts of olive mill wastewater (OMW) yearly in a short period (250 000 m 3 of liquid wastes in four months, November–February). Phenolic compounds are largely responsible for the phytotoxicity and antimicrobial effects of OMW. Several studies have been carried out on biological and enzymatic treatments of OMW. However, the use of OMW to produce value-added products, e.g. mushroom cultivation, are less explored. This research aimed to select shiitake mushroom strains capable of growing on OMW, involving decolorization, removal of total phenol, and high production of mycelial biomass. Sixteen strains of Lentinula edodes were evaluated for their tolerance to OMW, apical growth rate, and biomass production on agar media. The highest biomass yields were recorded in four strains (Le118, Le119, Le121, Le122) grown in the presence of 20% (v/v) OMW. The ability of these pre-selected strains to decolorize and to remove total phenol from OMW was then assessed in liquid culture, without nutritional supplements. The strain Le119 of L. edodes showed 65% decolorization, and 75% elimination of total phenol according to the Folin–Ciocalteu assay. Laccase production was the main lignolytic activity observed, and one of its isoforms stained on native PAGE with p-phenylenediamine as substrate at pH 5.0.