LOW GRAVITY AND INERTIAL EFFECTS ON THE GROWTH OF ESCHERICHIA-COLI AND BACILLUS-SUBTILIS IN SEMISOLID MEDIA

Background: Several published experimental results have shown that cul tures of suspended bacteria exhibit increased growth in the spacefligh t environment. Hypothesis and Methods: To test whether these differenc es were due to fluid mechanics and not cellular effects, E. coli and B . subtilis were grown on agar cultures under static, agitated, and rot ated conditions in the laboratory, and under low-gravity conditions on four Space Shuttle flights. Growth experiments were terminated with g lutaraldehyde, and individual cells were counted after quantitative el ution from the agar. Results: The spaceflight results, in conjunction with static, rotation, and agitation experiments indicate that E. coli and B. subtilis cultures on agar, unlike their suspension grown count erparts, do not experience heightened final cell concentration when th e inertial environment is changed. Conclusions: This finding points to fluid dynamics and extracellular transport phenomena and not cellular dynamics as the most likely cause of previously reported increases in bacterial growth in microgravity.