[60]

SPECIFIC GRAVITY OF SACCHAROMYCES CEREVISIAE USING STOKES LAW.  J.P.Kizito¹, K.L. Barlow¹, E.S. Nelson², F.M.Donovan³, N.D. Searby⁴, D. Vandendriesche⁴.  ¹National Center for Microgravity Research for Fluids and Combustion, and ²NASA Glenn Research Center, Cleveland, OH; ³Lockheed Martin and ⁴NASA Ames Research Center, Moffett Field, CA.

   Saccharomyces cerevisiae is an ideal eukaryotic micro-organism for biological studies with well defined genetic systems.  The properties of S. cerevisiae and its YPD growth media were obtained to analyze the fluid dynamics of the Cell Culture Unit (CCU) being developed by NASA Ames. 
   The media density was collected from mass vs. volume data.  The density of YPD media at 23.5°C and 30.0°C is 1.008 and 0.994 g/mL, respectively, with an error of ±0.005 g/mL. Media viscosity was determined using ASTM standards and, at 23.5°C and 30.0°C, the dynamic viscosity is 1.081 and 0.940 PaЧs, respectively.  Uncertainty in the viscosity data with a 95% confidence interval is ±0.17%.
   Yeast sedimenting through YPD media were used to determine the diameters and velocities of a population of cells.  Stokes law, represented by a force balance of a cell falling through a given fluid, subject to its own weight, buoyant force, and viscous drag, was used to develop an expression for yeast density.  For the population (n = 44), the measured mean cell diameter was 6.74 ± 0.85 m, the mean sedimentation velocity was 5.16 ±1.87 m/s, and the mean density of the cell was 1.22 ± 0.05 g/mL.
   The variances in the diameter and sedimentation velocity represent a real distribution of values in the population which are relatively large standard deviations when compared to the variance of density.  The variance in diameter is expected because yeast cells were at different stages in their growth cycle.  Most importantly, the ultimate density of yeast has a small standard deviation.

(Supported by NASA ARC Cell Culture Unit project)