Identification of new selenium compounds produced by edible mushrooms

The ability of two common edible mushroom species, Pleurotus ostreatus and Hericium coralloides, to metabolize selenium when grown in the presence of selenite (Se(IV)) and selenate (Se(VI)) was investigated. The efficiency of selenium absorption was 4-8 times higher when Se(IV) was used as selenium source. Anion-exchange HPLC-ICP-MS showed complete (>98.5 %) metabolization of Se(IV) to organic forms, while non-metabolized Se(VI) reached 8-18 %, depending on the species. Metabolized selenium was principally (>40 %) recovered as water-soluble species, followed by ∼20 % in water-insoluble polysaccharides and ∼ 10 % in water-insoluble proteins. Selenomethionine was the most abundant species in P. ostreatus, accounting for over 45 % of absorbed selenium and much less abundant (15-18 %) in H. coralloides. The water-soluble selenometabolome, accounting for 40-60 % of selenium in the samples, was characterized by HILIC with ESI-MS, revealing the presence of ten additional metabolites. These included several selenoneine derivatives and vinyl-selenocysteine-containing dipeptides, suggesting previously unreported pathways for selenium metabolism in mushrooms.