The influence of microgravity on repair of radiation-induced DNA damage in bacteria and human fibroblasts.

The influence of the space flight environment, above all microgravity, on the repair of radiation-induced DNA damage was examined during the Spacelab mission IML-2 as (1) rejoining of DNA strand breaks induced by X irradiation in cells of Escherichia coli B/r (120 Gy) and (2) in human fibroblasts (5 and 10 Gy); (3) induction of the SOS response after gamma irradiation (300 Gy) of cells of Escherichia coli PQ37; and (4) survival of spores of Bacillus subtilis HA 101 after UV irradiation (up to 340 J m(-2)). Cells were irradiated prior to the space mission and were kept frozen (E. coli and fibroblasts) until incubation for defined periods (up to 4.5 h) in orbit; thereafter they were frozen again for laboratory analysis. Germination and growth of spores of B. subtilis on membrane filters was initiated by humidification in orbit. Controls were performed in-flight (1g reference centrifuge) and on the ground (1g and 1.4g). We found no significant differences between the microgravity samples and the corresponding controls in the kinetics of DNA strand break rejoining and of the induction of the SOS response as well as in the survival curves (as proven by Student's t test, P < or = 0.1). These observations provide evidence that in the microgravity environment cells are able to repair radiation-induced DNA damage almost normally. The results suggest that a disturbance of cellular repair processes in the microgravity environment might not be the explanation for the reported synergism of radiation and microgravity.