INHIBITION IN A MICROGRAVITY ENVIRONMENT OF THE RECOVERY OF ESCHERICHIA-COLI-CELLS DAMAGED BY HEAVY-ION BEAMS DURING THE NASDA ISS PHASE-I PROGRAM OF NASA SHUTTLE MIR MISSION NO.-6

We participated in a space experiment, part of the National Space Deve lopment Agency of Japan (NASDA) Phase I Space Radiation Environment Me asurement Program, conducted during the National Aeronautics and Space Administration (NASA) Shuttle/Mir Mission No. 6 (S/MM-6) project. The aim of our study was to investigate the effects of microgravity on th e DNA repair processes of living organisms in the 'Realtime Radiation Monitoring Device III (RRMD III)' in orbit. Heavy ion beam radiation- or gamma-irradiation-damaged biological samples of Escherichia coli an d the radioresistant bacterium Deinococcus radiodurans were prepared a nd placed in a biospecimen box, which was loaded into the RRMD III sen sor unit of the Space Shuttle 'Atlantis'. Two identical sets of sample s were left in the SPACEHAB'S Payload Processing Facility (SPPF) in Fl orida, USA, as a control. 'Atlantis' (flight No. STS-84) was launched from NASA John F. Kennedy Space Center (KSC) in Florida, USA, on May 1 5, 1997. The mission duration was 9.22 days. An astronaut activated th e biological samples in the biospecimen box in the SPACEHAB during orb it in order to start repair of the DNA damaged by heavy ion beams or g amma-irradiation and the samples were incubated for 19 h 35 min at abo ut 22 degrees C, the cabin temperature. The control specimens in the S PPF were subjected to the same treatment under terrestrial gravity. Af ter 'Atlantis' returned to earth, we investigated cell recovery by com paring the repair of the radiation-damaged DNA of E. coli and D. radio durans in the microgravity environment in space with that on Earth. Th e results indicated that the DNA repair process of E. coli, but not of D. radiodurans, cells was inhibited in a microgravity environment.