Se-Enriched Mycelia of Pleurotus ostreatus: Distribution of Selenium in Cell Walls and Cell Membranes/Cytosol

The incorporation of Se to fungi has been studied, focusing on element distribution among different cellular compartments and, in particular, polysaccharide structures contained in cell walls. Se-enriched mycelia of Pleurotus ostreatus were obtained in submerged cultures. The incorporation of selenium from the growth medium to mycelia was observed with the relative distribution between cytosol plus cell membranes fraction (CCM) and cell walls fraction (CW) of about 44 and 56%, respectively. CCM fractions were analyzed by size exclusion chromatography with on-line UV (280 nm) and ICP-MS detection (80Se). The results obtained showed selenium binding to components of different molecular masses (about 24% of total selenium coeluted with the compounds of molecular mass > 10 kDa). A polysaccharide-containing fraction of mycelia was treated alternatively with Tris-HCl at pH 7.5 or with chitinase. Better solubility and increased contribution of low molecular mass compounds were observed in chitinase extracts (UV detection), confirming the degradation of polysacharides by the enzyme. The total area under the ICP-MS chromatogram of chitinase extract was 2 times higher with respect to the area for Tris-HCl extract. Furthermore, the relative contribution of selenium in the low molecular mass fraction (molecular mass < 1 kDa) in chitinase extract was 72% as compared to 45% in Tris-HCl extract (based on peak area measurements with respect to total area under the chromatogram). The results obtained suggest selenium binding to chitin-containing polysaccharide structures in fungi cell walls.