[Survival conditions of microorganisms under extremely severe environment]

The survival conditions of microorganisms under extremely severe environment are of interest in various areas of biology, sterilization, and space engineering, especially where resistance to microorganisms is concerned. Despite the interest, the resistance to microorganisms under extremely severe environment such as space environment or other planetary environment is not known well. In order to investigate survival conditions of microorganisms under extremely severe environment, surviving fractions for spores and vegetative cells of Bacillus subtilis were surveyed in various chemical species of atmosphere at various pressures and various temperatures, and the dependence on time for surviving fractions was examined. The results show: (i) Surviving fractions depend on chemical species of atmosphere. (ii) At high pressure and high temperature, surviving fractions are low and the resistance of spores is stronger than that of vegetative cells. (iii) Surviving fractions decrease as first-order reaction along with time elapsed.