[BAO01-P08] Survivability and DNA damage of Deinococcus spp. in cell-aggregates exposed to space in Tanpopo mission
Keywords:Tanpopo mission, Surviving fraction, DNA damage
[Method] Dried deinococcal cell-aggregates in wells of aluminum plates were exposed to space for about one year. The dried cells were resuspended in phosphate buffer and recovered from wells. The cell suspension was inoculated to mTGE agar and incubated at 30ºC before enumerating colonies. The surviving fraction was calculated as the number of viable cells after exposure divided by the number of viable cells without exposure.
[Result and Conclusion] Although the D. radiodurans R1 cell-aggregates with less than 100 μm- thickness exhibited a low survival rate, those with more than 500 μm-thickness was well-survived (Fig. 1). It was suggested that DNA damage in the cell-aggregates with more than 500 μm-thickness are readily repaired by homologous recombination and excision repair systems. The surviving fractions of the ground control and the space exposed cell-aggregates with 1000 μm-thickness were comparable. The result might reflect intracellular moisture content that was removed by a long-time space exposure. Low moisture content will help cells to survive in space. From these results, we concluded that the deinococcal cell-aggregate with 500 μm-thickness is sufficient to shield UV, thus surviving for more than one year in space. DNA damage caused in space was mainly base damage such as pyrimidine dimer caused by UV irradiation and double strand breaks.
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