Lethality of high linear energy transfer cosmic radiation to Escherichia coli DNA repair-deficient mutants during the 'SL-J/FMPT' space experiment

We investigated the lethal and mutagenic effects of high linear energy transfer cosmic radiation on 11 strains of Escherichia coli, including DNA repair-deficient mutants, using the Radiation Monitoring Container and Dosimeter in the space shuttle `Endeavour' as part of the `SL-J/FMPT' space experiment, the `Fuwatto '92' project. After the return to earth of the shuttle, we evaluated survival and mutations of samples in space and matched controls. The surviving fractions were determined by means of colony count on broth agar plates, and the mutation frequencies were estimated by appearance of arg⁺ revertants on minimal agar plates. The average of the total equivalent dose rate during this space flight was 0.202 mSv/day as measured by the plastic radiation detectors and the thermoluminescent dosimeters in the Radiation Monitoring Container and Dosimeter. The combined action of DNA polymerase and 3′→5′ exonuclease activities was found to make the greatest contribution to the repair of cosmic radiation-induced DNA damage, 5′→3′ exonuclease and recombination repair enzyme activities made a moderate contribution, whereas UV endonuclease activity was not involved in this DNA repair process.