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COMPUTATIONAL MODELING OF EXTRACELLULAR MASS TRANSPORT.  M.R. Benoit¹, D.M. Klaus¹, and E.S. Nelson².  ¹Dept of Aerospace Engineering Sciences, University of Colorado at Boulder.  ²Computational Microgravity Laboratory, NASA Glenn Research Center, Cleveland, OH.

   Spaceflight has been shown to induce various alterations in the growth kinetics of bacterial cultures, including shortened lag phase and higher final cell population density.  The specific causal mechanisms for the differences between flight and ground control samples, however, have yet to be positively determined.  It has been proposed that changes in the fluid environment immediately surrounding the cell (as a consequence of altered mass transport processes similar to those governing protein crystal growth) may be indirectly responsible for the unique microbial responses observed to occur in space.
   The objective of the present study is to establish a mathematical model incorporating the essential relationships influencing extracellular mass transport that are thought to affect microbial metabolism. The model should predict specified parameters relevant to altered growth kinetics under varying levels of gravity. The linear momentum equation and species concentration equations for nutrients and byproducts that govern mass transport have been applied to a test case of E. coli cultured in minimal growth media.  Solutions have been obtained using the continuum mechanics solver COMET™.
   The model currently generates a buoyant plume of less dense metabolic byproducts in a 1g simulation. The velocity of the plume compares favorably to previous experimental and quantitative theoretical work. Initial results suggest that numerical analysis can serve as a valid tool for studying the complex interplay of forces and resultant mass transport phenomena that act on growing cells.
   Future plans include incorporation of multiple interacting microbes, extending the problem to 3-D, increasing sophistication of the metabolic model, and adding microbial movement, including Brownian motion, sedimentation and random (swimming) motility.

(Supported by NASA: NGT5-52386)