Selenium stress in Ganoderma lucidum: A scanning electron microscopy appraisal

The present investigation explores the effect of selenium supplementation on radial growth and ultrastructural alterations in the hyphae and spores of Ganoderma lucidum. A concentration dependent decrease in radial growth was observed on culturing G. lucidum on sodium selenate supplemented mushroom minimal agar post 24 h. However, in comparison to control, selenium supplementation slightly increased diameter of radial growth till 10 ppm after 48 h. The Scanning Electron Microscopy (SEM) studies of radial growth showed selenium concentration dependent gradual decrease in hyphal diameter suggesting thinning and extensive branching of mycelia in response to increased Se supplementation. Moreover, SE micrographs also depict selenium concentration dependent decrease in number of spores and spore size. A significant decrease in spore diameter was recorded for mushroom minimal agar supplemented with 20 and 25 ppm (5.64 and 1.26 μm, respectively) as compared to control (10.04 μm). The spore were morphologically altered from spherical to oval or oblong and inflated to constrict deformed on increasing selenium concentration. SEM-energy dispersive X-ray spectroscopy (SEM-EDS) studies of intact mycelia showed no traces of selenium. However, crushed mycelia samples exhibited Se signals probably due to presence of selenium as integral component of cytosolic moieties like selenoproteins. Atomic absorption spectroscopy (AAS) of mycelia showed an increasing trend in the uptake of selenium with increased selenium supplementation. Percentage absorption was found to be in range of 7.2 - 9.9% with maximum absorption at concentrations of 15 and 25 ppm. Hence, sodium selenate supplementation at 10 ppm (with maximum 15 ppm) can be used for Se fortification as Ganoderma can grow rapidly without significant alteration in structure and morphology to enhance its biomedicinal properties.