Cryopreservation: fundamentals, mechanisms of damage on freezing/thawing and application in culture collections.

A variety of approaches including drying, freeze- drying/lyophilization and cryopreservation have been utilized for the long-term maintenance of microalgal and cyanobacterial cultures, however, only cryopreservation, the storage of material at ultra-low temperatures, has the potential to guarantee long-term stability of the preserved algae. The process of cryopreservation is intrinsically injurious and optimization requires the balancing of "solution" stresses encountered during slow cooling and intracellular ice formation on rapid cooling. This paper outlines the various strategies that may be employed to preserve algae, the effects of ultra- low temperatures on algae and briefly introduces some novel approaches that may widen the applicability of cryopreservation to currently freeze-recalcitrant taxa.