[M-IS03] Astrobiology

[MIS03-P06] Wet heat sterilization test of microbes for planetary protection

*Riku Takai¹, Kosuke Fujishima^2,3, Shino Suzuki^4,5, Shunta Kimura^4,5 (1.Keio University, 2.Tokyo Institute of Technology, Earth-Life Science Institute, 3.Graduate School of Media and Governance, Keio University, 4.Institute of Space and Astronautical Science , 5.Space Exploration Innovation Hub Center, Japan Aerospace Exploration Agency)

Keywords:planetary protection, bioburden reduction, wet heat sterilization

In space exploration, it is essential to reduce the number of live microbial cells to prevent contamination of Earth's microbes into celestial bodies. Dry heat is one of the most practical method of sterilization for space crafts. However, since some components of space crafts cannot withstand high temperatures, it is necessary to consider sterilization techniques other than dry heat. Wet heat sterilization can be an alternative method to dry heat sterilization because it can be performed at lower temperatures and in a shorter time than dry heat. Although results of wet heat sterilization tests on several microbes have been reported, comparative studies of wet heat resistance of microbes that can survive in space environments have not been conducted. This study aims to compare the wet heat resistance of microbes, which are essential for planetary protection. Bacillus atrophaeus spores, Brevundimonus diminuta, and Deinococcus radiodurans suspended in liquid media were placed in microtubes and exposed to heat on a heat block of 60-120°C. After heat exposure, microbes were applied onto agar medium and incubated for 3 days at 30°C. The number of colonies was counted to evaluate viable cells. B. diminuta and D. radiodurans were quickly sterilized at 80°C. B. atrophaeus spores showed higher resistance than the other two species; it survived exposure to 80°C for 120 minutes but was quickly sterilized at 120°C. Temperature-dependent effects were indicated in wet heat sterilization. It was also confirmed that wet heat could sterilize microbes at lower temperatures and in a shorter time than our other experimental results of dry heat sterilization.