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Simple Technique for Drying Yeast for Long-Term Ambient Storage. D.S. Yu1, B. Girten2 and J. Cohen3. 1Lockheed Martin Space Operations, 2NASA Headquarters, 3Univsersities Space Research Association-NASA headquarters, NASA Ames Research Center, Life Sciences Division, Moffett Field, CA.

   In preparation for potential long-term yeast space flight opportunities, a procedure was developed to obtain viable yeast after storage in a dried state at ambient temperature for several months on-orbit.  Optimization of this procedure examined three variables: 1) procedure used to process yeast prior to drying (culture media), 2) yeast drying substrate (filter type) and 3) medium for yeast dry down (chemical protective agents).  Yeast was cultured for 1 to 2 days, resuspended in different mixtures of chemical protectants, spotted on a filter and air dried in a BioSafety Hood prior to storage in a sterile microcentrifuge tube at ambient temperature.  At specific time points, samples were eluted with yeast: peptone: dextrose (YPD) media, spread on YPD plate and incubated to determine the percent survivability of the yeast sample.  The data suggests that yeast cultured in sporulation media survived the drying process better than those cultured in YPD.  Among the selected chemical protectants tested, it was determined that yeast dried in a mixture of skim milk and trehalose had a higher percent survivability when compared to skim milk or trehalose alone.  In the optimized procedure, the percent viability of the yeast sample after storage at ambient temperature for 84 days is 92+32.1%.  At 153 days, viability was at 54.6+13.4% and appeared to stabilize at 242 days where viability was 54.9+23.4%.  Overall, the proposed yeast ambient temperature technique is quick, inexpensive and does not require specialized equipment.  This technique may be useful for any future long-term flight payloads that require storage of yeast for several months prior to activation.