Scanning Electron Microscopy of Algal and Fungal Cells

Scanning electron microscopy (SEM) was used to visualize the algal and fungal cells. The cells were washed with 0.1 M phosphate buffer, pH 7.0, followed by fixation in 4% glutaraldehyde. After 4 h of incubation at room temperature, the cells were washed again in the same buffer, suspended in a 1% OsO₄ solution, and incubated for 30 min. Dehydration was carried out using increasing concentrations of acetone (successively 30%, 50%, 70% and twice 100% for 30 min). The cell suspension was placed on microscope stages covered with carbon discs. The samples were then dried on silica gel in a desiccator for 24 h. The silica gel was previously prepared by incandescence in an oven at 121 °C for 2 h. The surface of the tables with algal cells was gold coated with a K550X sputtering machine (Quorum Technologies, United Kingdom). Samples with algal cells were then analyzed using a Tescan Vega 3 scanning electron microscope (Tescan Orsay Holding, Czech Republic)^{28 (link)}. The A. nordenskioeldii cells were not dried, but when samples immersed in acetone were applied to the carbon discs, they were directly inserted into the vacuum chamber of the Quanta 3D FEG high-resolution scanning electron–ion microscope (FEI Company, Hillsboro, USA) and immediately analyzed to minimize the negative effects of drying.