Optimization of cryopreservation conditions for the unicellular red alga Cyanidioschyzon merolae

Cryopreservation is essential for maintaining stable stocks of organisms. We report the development of a method for cryopreservation of the unicellular red alga Cyanidioschyzon merolae, a model organism for the investigation of the basic architecture of photosynthetic eukaryotes. Glycerol, dimethyl sulfoxide and methanol were examined for their ability to protect the cell from cryoinjury and/or cytotoxicity. It was found that methanol was the most effective as a cryoprotectant for C. merolae. After the optimized setting of parameters such as working concentration of cryoprotectant and the period of slow cooling, cultures were supplemented with 5% (v/v) methanol and frozen by slow cooling using a passive-freezing unit, followed by plunging into liquid nitrogen. We found C. merolae cells retained greater than 80% viability for at least 83 days in storage.