Induction of lysogenic bacteria in the space environment

摘要

The Biosatellite 2 experiment using the lysogenic bacterium Salmonella typhimurium was designed to test the hypotheses that weightlessness, both with and without gamma irradiation, would affect bacterial cell growth or induction of bacterial prophage. The bacterial data were analyzed by three methods: analysis of variance, t tests between flight and earth control data (where t is the percentage difference between experiment and control sets), and graphic presentation. The data on bacterial growth led to rejection of the hypotheses; space flight produced both increased density of Salmonella typhimurium when grown in liquid medium and interaction to give greater resistance to gamma irradiation at levels between 265 and 1648 R total dose (17 and 103 R per average cell generation). Tests of other variables eliminated all but weightlessness in accounting for the difference. On the basis of the t tests there was no difference in the free phage per bacterium produced under conditions of control and those of flight. The induced bacteriophage per viable bacterium showed significant differences between flight and control at two radiation levels (265 and 645 R). The flight set had consistently lower yields at all levels of radiation.