In connection with planetary quarantine, we are studying how terrestrial microorganisms can survive in the cosmic environments. If comon terrestrial microorganisms can not survive in the space even for a short period, we can reduce the cost for sterilizing space probes. The interstellar environments has been simulated by using ultra low temperature high vacuum ( 77 K, 10^-6 torr ) improved crynostat and ptoton irradiation from Van de Graaff genarator in the Tokyo Institute of Technology. Various species of terrestrial microorganisms, virus, bacteria, actinomycetes, yeast and fungi were tested quantitatively inactivity under simulated space conditions. After exposing a barrage of the protons corresponding to 250 years irradiation in Space, it was shown that spores of Bacillus subtilis and Aspergillus niger and tabaco mosaic virus can survive about 45%. 25% and 82%, respectively. The results are consistent to report by Weber and Greenberg that spore of B. subtiIis survived 10% under simulated conditions after UV irradiation corresponding to 500 years exposure in space. It might be presumed that the survived terrestrial microorganisms come back to mother earth in future as pathogenic mutants by irradiation of cosmic rays.

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Development of fish eggs (Oryzias latipes) will be studied in a small unmanned space platform SFU (Space Flyer Unit) launched by Japan around 1993. In such experiments, to assess the microgravity effects justly, radiation effects on the fish embryos should be investigated beforehand. We irradiated the fish embryos (at the developmental stage 11 of this species) with proton beams (5.7 MeV) generated by a tandem-type Van der Graaff accelerator. The relationship between the dose delivered by protons and the percentage of hatching fry was established. The energy loss of protons after passing Mylar foil of different thickness was measured. More embryos survived when they were irradiated with protons after a thick Mylar foil. From consideration of the geometry of the fish eggs, it was supposed that embryos received proton energy at a plateau portion before the Bragg peak.

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We are irradiated with cosmic rays at about 280 uSv a year as natural background on the earth. It has been calculated on trial that the irradiation dose by cosmic rays presumably increase to be about 40 mSv when we stay in space station for 6 months, which is higher than 50 mSv a year, the dose limit for radiation workers. Radiation produces a wide range of different types of damages of DNA and induces mutation. Mutation is the result of error in the process of repair and replication of DNA. Mechanism of mutation induction has been studied in detail in Escherichia coli. Genes such as uvrA, B and C, and umuC/D express in the cells inducing SOS response, resulting in enhancement of repair capacity and of mutagenesis. Although enhancement of the capacity of DNA repair is observed in UV- or radiation-irradiated mammalian cells, it dose not presumably associate enhancement of mutagenesis. Mechanism of mutation induction in mammalian cells may be different from that in bacterial cells. Base substitution mutations are predominantly detected in plasmid or phage DNA replcating in E. coli. GC to AT transition is most frequent base substitution. Large deletion of DNA fragment in addition to base substitution and frameshift are observed in irradiated mammalian cell. Further studies should be performed on radiation-induced mutagenesis at molecular level.

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Treatment of Escherichia coli and Salmonella typhimurium cells with a low dose of hydrogen peroxide induces expression of a large number of genes, and confers the cells resistance to oxidative stresses. The oxyR gene encodes a positive regulatory protein for a subset of these genes involved in the defense against the oxidative damage. We cloned a DNA fragment that contains the E. coli oxyR region on a plasmid vector, and analyzed the nucleotide sequence of the gene. The amino acid sequence of OxyR protein shows an high degree of homology to the sequence of a number of bacterial protein including LysR, IlvY, MetR and NodD. OxyR protein specifically bound to the upstream regulatory regions of the oxyR and katG genes as demonstrated by the gel-retardation assay and the DNase I footprinting experiment. Experiments with gene fusion indicate that OxyR protein functions as a repressor for oxyR, in addition to its known function as a transcriptional activator for the genes in the oxyR regulon.

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