**ASGSB 2003 Annual Meeting Abstracts**

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SPECIFIC
GRAVITY OF *SACCHAROMYCES CEREVISIAE *USING STOKES LAW.
J.P.Kizito^{1}, K.L. Barlow^{1}, E.S. Nelson^{2},
F.M.Donovan^{3}, N.D. Searby^{4}, D. Vandendriesche^{4}.
^{
1}National
Center for Microgravity Research for Fluids and Combustion, and ^{2}NASA
Glenn Research Center, Cleveland, OH; ^{3}Lockheed Martin and ^{4}NASA
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 Pa×s,
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)