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Containment Geometry Considerations for Space Flight and Simulated Microgravity Microbiology Experiments.   H.N. Howard and D.M. Klaus, Dept. of Aerospace Engineering Sciences, University of Colorado, Boulder, CO.

   Suspension cultures of non-motile bacteria grown in space flight have been consistently shown to exhibit decreased lag phase durations and increased final population densities compared to ground controls.  Reduced fluid mixing in microgravity, resulting from the absence of sedimentation and convection, is hypothesized to be a primary causal factor of these observed responses.  Ground-based methods used to maintain 1g control cultures might indirectly contribute to the net influence that sedimentation and convection exert on bacterial growth.

   Containment geometry factors, for example, can be shown to affect suspension culture bacterial growth.  This study characterized containment geometry (aspect ratio) effects on E. coli (ATCC 4157) growth under a variety of experimental conditions.  In general, horizontally oriented suspension cultures in sufficiently tall, thin containers were found to reach significantly higher final population densities than otherwise comparable, but vertically oriented cultures.

   Culture orientation can significantly impact microbial growth experiment results and should be carefully considered when designing controls for space flight and ground-based analog experiments.  Controls for clinostat and HARV studies have typically been limited to rotating cultures oriented 90º (i.e., about a vertical axis) with respect to the experimental cultures.  Rotating controls may provide an indicator of rotational shear stress effects, however, containment geometry effects may introduce additional experimental variables that are not appropriately accounted for during comparison of the results.  Inclusion of horizontally and vertically oriented static controls may enable researchers to more clearly distinguish between effects related to shear stress, containment geometry (aspect ratio) and simulated or actual microgravity phenomena.

(Supported by BioServe Space Technologies NASA NCC8-242 and NASA GSRP NNJ04JF86H)