DNA-REPAIR IN MICROGRAVITY - STUDIES ON BACTERIA AND MAMMALIAN-CELLS IN THE EXPERIMENTS REPAIR AND KINETICS

The impact of microgravity on cellular repair processes was tested in the space experiments REPAIR and KINETICS, which were performed during the IML-2 mission in the Biorack of ESA: (a) survival of spores of Ba cillus subtilis HA101 after UV-irradiation (up to 340 J m(-2)) in the experiment REPAIR; (b) in the experiment KINETICS the kinetics of DNA repair in three different test systems: rejoining of X-ray-induced DNA strand breaks (B1) in cells of Escherichia coli B/r (120 Gy) and (B2) in human fibroblasts (5 and 10 Gy) as well as (B3) induction of the S OS response after gamma-irradiation (300 Cy) of cells of Escherichia c oli PQ37. Cells were irradiated prior to the space mission and were ke pt in a non-metabolic state (metabolically inactive spores of B. subti lis on membrane filters, frozen cells of E. coli and human fibroblasts ) until incubation in orbit. Germination and growth of B. subtilis wer e initiated by humidification, E. coli and fibroblasts were thawed up and incubated at 37 degrees C for defined repair periods (up to 4.5 h) , thereafter they were frozen again for laboratory analysis. Relevant controls were performed in-flight (1 x g reference centrifuge) and on ground (1 x g and 1.4 x g). The results show no significant difference s between the microgravity samples and the corresponding controls neit her in the survival curves nor in the kinetics of DNA strand break rej oining and induction of the SOS response (proven by Student's t-test, 2 P = 0.05). These observations provide evidence that in the micrograv ity environment cells are able to repair radiation-induced DNA damage close to normality. The results suggest that a disturbance of cellular repair processes in the microgravity environment might not be the exp lanation for the reported synergism of radiation and microgravity.