Cryopreservation of Marine Unicellular Algae. I. A. Survey of Algae with Regard to Size, Culture, Age, Photosynthetic Activity and Chlorophyll-to-Cell Ratio

Abstract

About a dozen species of marine unicellular algae were cultivated under constant growth conditions and tested for their ability to survive freezing in liquid nitrogen. All species survived uncontrolled direct freezing in liquid nitrogen poorly; however, the addition of a cryoprotective agent, dimethylsulfoxide (DMSO), and the application of a two-step cooling procedure enhanced the freezing resistance of most algae. Optimal conditions for two-step cooling were initial cooling in 5 '/o dimethylsul- foxide to -30 "C, then freezing in liquid nitrogen, and finally thawing at 30 OC. Freezing tolerance of viable algae was not related to culture age, photosynthetic activity or chlorophyll-to-cell ratio, but rather was specifically related to the algal species, and in a few cases to the algal size and to the specific growth rate. These observations indicate that the cryopreservation capability of unicellular marine algae is closely related to the intrinsic characteristics of the algae and to certain cellular properties of the cell. chrysophytes.