[8]

Coupled Effects of Temperature and Simulated Microgravity (Clinostat) on E. coli Population. F.N. Ahmed, H.N. Howard and D.M. Klaus, University of Colorado, Boulder, CO 80309

   In an attempt to reproduce previous results from Brown et al. (2002) describing the effect of simulated microgravity (using clinorotation) on E. coli population growth, our initial outcomes were inexplicably inconsistent. Upon further analysis, however, an interesting trend was identified between the temperature at which the cultures were grown and the corresponding response to clinorotation that occurred. It was consequently hypothesized that E. coli cell size and growth rate concomitantly contributed to the net effect of simulated microgravity. Lewis and Trueba (1981, 1982) showed that the temperature at which E. coli are grown influences their size. Additionally, Woldringh and Kubitschek (1981, 1984) showed that cell density and shape stay relatively constant despite the changes in size with temperature. These relationships imply that larger cells will sediment faster, hence, should exhibit a greater response when sedimentation is prevented by clinorotation. In subsequent experiments over a range of temperatures, we found that non-motile E. coli cells grown on a clinostat experienced maximal final population differences at 30ºC relative to static controls. These findings suggest that E. coli cell size, as a function of temperature-dependent growth rate, plays an important role in the overall influence of gravity on cell population. Studies are now aimed at correlating sedimentation to clinostat results. (Supported by UROP and BioServe)