TOLERANCE OF 6 MARINE MICROALGAE TO THE CRYOPROTECTANTS DIMETHYL-SULFOXIDE AND METHANOL

Knowledge of tolerance to cryoprotectants is important in determining viability after biobogical freezing of algae. Six taxonomically divers e marine microalgae were evaluated for their tolerance to the widely u sed cryoprotectants dimethyl sulfoxide (DMSO) and methanol. Tetraselmi s chuii Butcher survived exposure to 30% (v/v) DMSO and 25% methanol f or periods of up to 4 h. AIL other species were more sensitive to high concentrations of these cryoprotectants. DMSO was lethal at 25% after a 15-min exposure of Rhodomonas baltica Karsten, Isochrysis aff. galb ana (strain T-ISO) Parke, and Nannochloropsis gaditana Lubian. Nannoch loris atomus Butcher could tolerate only a I-min exposure at this conc entration; Chaetoceros gracilis Schutt completely lost viability when exposed to 20% for 60 min. Safe concentrations for DMSO incubations we re similar (about 5% lower) to lethal thresholds. Methanol incubations did not significantly decrease cell viability at concentrations of 5% (1 min)for R. baltica, 25% (up to 60 min) for T. chuii, 15% (up to 12 0 min) for I, galbana, 5% (up to GO min) for N. gaditana, 15% (up to 2 40 min) for Ch. gracilis, and 15% (up to 120 min) for N. atomus. Nanno chloris atomus has the potential to be cryopreserved without the need for any cryoprotectant. The other five species were clearly dependent on a 15% DMSO preincubation to achieve a growth response after thawing from -196 degrees C. Only N. atomus and N. gaditana could be grown af ter being cryopreserved in the presence of 5% methanol.