Botryococcus braunii Kützing, a green colonial microalga, occurs worldwide in both freshwater and brackish water environments. Despite considerable attention to B. braunii as a potential source of renewable fuel, many ecophysiological properties of this alga remain unknown. Here, we examined the desiccation and temperature tolerances of B. braunii using two newly isolated strains BOD-NG17 and BOD-GJ2. Both strains survived through 6- and 8-month desiccation treatments but not through a 12-month treatment. Interestingly, the desiccation-treated cells of B. braunii gained tolerance to extreme temperature shifts, i.e., high temperature (40 °C) and freezing (-20 °C). Both strains survived for at least 4 and 10 days at 40 and -20 °C, respectively, while the untreated cells barely survived at these temperatures. These traits would enable long-distance dispersal of B. braunii cells and may account for the worldwide distribution of this algal species. Extracellular substances such as polysaccharides and hydrocarbons seem to confer the desiccation tolerance.
Keywords: Algal dispersal; Botryococcus braunii; Desiccation tolerance; Polysaccharide; Temperature tolerance.