Cultivation of Saccharomyces cerevisiae in a bioreactor in microgravity.

Yeast cells were cultured for 8 d in a newly developed bioreactor during the Spacelab IML-2 mission. Two bioreactors, one stirred and one without stirring, were installed in the Biorack facility in space. Two control units were installed in the Biorack module at the Kennedy Space Center. Samples were drawn on mission day 3, 5, 6, 7 and 8 and preserved either by freezing or chemically fixed for post-flight analysis. The values of pH, pH regulation, temperature and redox potential were transmitted on-line to the ground station throughout the mission. The performance of the bioreactor was satisfactory except for a partial failure of the medium micropump. Despite the failure of the pump, the data support the following conclusions: There is a significant difference in the distribution of the bud scars between cells cultured at 0 x g and at 1 x g. The percentage of randomly distributed bud scars was significantly higher in the flight (17%) than in the ground control cells (5%). No remarkable differences were noted in the cell cycle, ultrastructure, cell proliferation, cell volume, ethanol production and glucose consumption.