Liquid nitrogen storage of yeast cultures. I. Survival, and literature review of the perservation of fungi at ultralow temperatures.

All 20 yeast strains of 17 species tested survived 75 days (the length of the experimental period) in liquid nitrogen at -196 C. The components of the more protective of the two freezing media used were (w/v) malt extract 2.5%, yeast extract 0.25%, peptone 0.5%, calf serum 15% (v/v) and dimethyl sulfoxide 10% (v/v). Viability of the cells in this medium after rapid uncontrolled freezing and thawing in selaed plastic ampoules ranged from 2% to 98% (average 67%) compared with the viability of the cultures before freezing. In only 4 strains was survival lower than 50%. (90 references).