Many unicellular microalgae and cyanobacteria are successfully cryopreserved by snap-freezing in liquid nitrogen. However, high survival rates have not been obtained for most filamentous multicellular microalgae and cyanobacteria. This study was conducted to attain high survival rates of Spirulina (Arthrospira) platensis NIES-46 after snap-freezing in liquid nitrogen by establishing a simple and reliable cryopreservation method. To this end, we investigated the dependence of the survival rate on trichome morphology and recovery from damage during preculture. The survival rate was estimated in the presence of 5% v/v dimethyl sulfoxide. The rate was higher for S. platensis NIES-46 with loosely coiled trichomes than for those with tightly coiled trichomes, and was higher for mutant with straight trichomes than with coiled trichomes. Although trichomes were damaged by agitation during preculture, the survival rate after cryopreservation by snap-freezing was improved by stationary culture before freezing. Ultimately, a high survival rate of approximately 80% was obtained for S. platensis NIES-46 after cryopreservation by snap-freezing in liquid nitrogen by considering trichome morphology.
