Cryopreservation of eukaryotic algae : a review of methodologies

Since pioneering work in the early 1960s, there has been growing interest and numerous experimental investigations into the cryopreservation of algal material. Mostly, these studies relate to the requirement for long term preservation and storage of algal material contained in culture collections or used in the seaweed mariculture industry. The present review deals with techniques used in the cryopreservation of biological samples and their application to both micro- and macroalgae. Methods for the prevention of cell damage and freezing injury during the cooling and low-temperature storage of algal material are discussed with reference to the effect on viability of such variables as cooling rates, final temperatures attained, the use of various types and concentrations of cryoprotectants, thawing rates, and storage times and temperatures. Some consideration is also given to the various methods used for increasing cell viability, including the induction of freezing tolerance. Cryopreservation protocols employed by numerous workers in this field are detailed, and concluding remarks are made on those techniques and conditions providing optimum viability of cryopreserved algae.