Optimization of freshwater microalgae (Scenedesmaceae, Chlorophyta) fixation method for primary taxonomic identification by scanning electron microscopy

Abstract

On the example of green microalgae of the family Scenedesmaceae Coelastrella rubescens, Coelastrella sp., Coelastrella aeroterrestrica, Pseudospongiococcum protocols and Desmodesmus sp. different fixation methods were tested for scanning electron microscopy in order to obtain images of taxonomically relevant cell surface structures (ribs, poles, spines, warts, etc.). Depending on the physiological state of the cells (young, actively dividing or at the secondary carotenogenesis stage), 0.5–2.5% glutaraldehyde in 0.15 M PBS, as well as in 5 and 6.67 mM phosphate buffer, were used for fixation. The pH range of the fixing reagent was 6,8–7,4. Dehydration was performed in graduated ethanol (20–100%). It was concluded that the SEM method is highly informative for the identification of Scenedesmaceae with a structured cell wall.