Development of thermal treatment for the extraction of extracellular polymeric substances from Microcystis: Evaluating extraction efficiency and cell integrity

Extracellular polymeric substances (EPS) play a crucial role in processes associated with the growth and survival of microorganisms, such as in colony formation of cyanobacterium Microcystis. Thermal treatment is an effective method for EPS extraction. However, intracellular materials, however, often contaminate EPS extracts, possibly owing to cell lysis during thermal extraction. In this study, EPS samples were extracted using boric acid buffer under different temperatures (45-75 degrees C) and extraction periods (15-30 min), and evaluated with respect to both extraction efficiency and cell integrity. Moreover, the method developed in this study was compared to two widely employed methods (thermal extraction with 0.05% NaCl or NaOH (pH = 10)) with respect to EPS yield and composition, cell integrity or the release of cellular inclusions, and changes in cell size and morphology. Results indicated that thermal extraction with the boric acid buffer achieved the highest EPS yield and the lowest cell lysis. The optimal results were achieved by treatment at 65 degrees C for 30 min. However, a large quantity of cell debris and released cellular inclusions were detected when the other thermal methods were used, which suggests that stabilizing the cellular osmotic pressure and pH can effectively improve EPS yield and minimize cell lysis during thermal extraction. The findings of this study improve the EPS extraction from Microcystis, which can foster further investigations on the functions of these substances in the formation of Microcystis blooms.