Study on the effects of cosmic environment on the recovery from radiation damages of bacteria

An experiment to elucidate the effects of space environment such as microgravity on the recovery from radiation damages in Deinococcus radiodurans, a bacterium highly resistant to radiation was designed and performed in the second international microgravity laboratory (IML-2). After exposure to 6OCo (2 - 12 kGy) on the ground, the bacteria were loaded to a space shuttle and under microgravity on the orbit the culture medium was added to the bacteria to allow the DNA-repairing reactions. The survival rate of such bacteria was compared to the rate for those left on the ground. The survival rate of the flight subjects were an order of magnitude larger than those of the control subjects left on the ground under the condition of 7 kGy or more of radiation dose, showing this result is inconsistent to the previous data. These results suggest that the repair reaction of radiation damages in D. radiodurans occurs more effectively in the space environment that on the ground. However, the stimulation of the DNA repair reaction under the microgravity was thought to be specific the radiation resistant bacteria, since the previous studies showing cooperative effects of radiation and cosmic ray on the repair of radiation damages were conducted using more complicated organisms, such as insects and plants. (M.N.)