Effects of space flight factors at the cellular level: results of the Cytos experiment.

Paramecium tetraurelia was cultivated aboard the Soviet orbital station Salyut 6. Each culture included one cell, bacterized culture medium, and two small glass tubes filled with a fixative. Cultures were kept at a low temperature before Soyouz-Salyut docking. Cultures were maintained at 25 degrees +/- 0.1 degree C in orbit and were fixed every 12 h. The space flight resulted in an increase in cell growth rate and in cell volume. Measurements of cell dry weight and total protein content favour a higher cell water content. Respective roles of cosmic rays and microgravity are discussed. Cytos results are compared to those of previous space experiments.