The effects of germanium and selenium on growth, metalloid accumulation and ergosterol content in mushrooms: experimental study in Pleurotus ostreatus and Ganoderma lucidum

Abstract

The aim of this study was to examine the effects of substrate supplementation with germanium (Ge) and selenium (Se), alone or combined, on the growth, element accumulation and ergosterol content in the fruiting bodies of the mushroom species Ganoderma lucidum and Pleurotus ostreatus. Both species were grown in four independent experimental systems with different concentrations of germanium powder (1, 5 and 10 mM), selenite [Se(IV)] and selenate [Se(VI)] (0.1, 0.4 and 0.8 mM of each Se species). Se supplementation caused no observable changes to morphology while the addition of Ge induced changes in size and/or colour, especially for P. ostreatus. A synergistic effect of Ge supplementation on Se accumulation in fruiting bodies of G. lucidum was observed only at the two highest levels of supplementation with both elements. Even though inorganic Se was used to enrich the experimental substrates, organic Se compounds dominated in the fruiting bodies. Increasing levels of Ge in the substrates elevated the content of organic selenium in the fruiting bodies of G. lucidum. No such trend was recorded in P. ostreatus. The maximum mean Ge levels in P. ostreatus and G. lucidum reached up to 70 and 80 mg kg−1, respectively. However, the bioaccessibility of this element was low, in the range 5.4–6.6% (P. ostreatus) and 0.4–7.6% (G. lucidum). Ergosterol content in the fruiting bodies of both species displayed the highest values in all the experimental systems supplemented with Se. The addition of Ge and Se + Ge resulted in losses of ergosterol content in comparison to cultivation with Se supplementation and control. The obtained results show the significant role of Ge–Se interaction in the accumulation of these elements in the studied mushroom species.