Deal P H, Souza K A, Mack H M
Orig Life. 1975 Oct;6(4):561-73. doi: 10.1007/BF00928904.
Jovian plants have enviroments apparently suitable for the evolution of life, but nevertheless, present severe challenges to organisms. One such challenge arises from the presence of ammonia. Ammonia is an efficient biocide, its effect being dependent on pH as well as on concentration. The effects of pH and ammonia concentration were studied separately, where possible, on a variety of organisms, including some isolated from natural enviornments of high pH and/or ammonia concentration. Escherichia coli and Bacillus subtilis are both extremely sensitive to ammonia. An aerobic organism (growth up to pH 11.4) from an alkaline spring is more resistant, but exhibits a toxic response to ammonia at a pH much lower than its maximum for growth. The greatest ammonia resistance has been found in an unidentified organism growing at near neutral pH. Even in this case, however, survival at ammonia concentrations reasonably expected on the Jovian planets is measured in hours. This is, nevertheless, two to three orders of magnitude longer than for E. coli. Our data support the tentative conclusion that contamination of the Jovian planets with terrestrial organisms that can grow is unlikely. However, the range of toxic response noted, coupled with the observation that terrestrial life has not been exposed to high ammonia concentrations for millions of years, suggests that adaptation to greater ammonia tolerance may be possible.
类木行星的环境显然适合生命进化，但尽管如此，仍对生物体构成严峻挑战。其中一个挑战源于氨的存在。氨是一种有效的杀菌剂，其效果取决于pH值和浓度。在可能的情况下，分别研究了pH值和氨浓度对多种生物体的影响，包括一些从高pH值和/或高氨浓度的自然环境中分离出来的生物体。大肠杆菌和枯草芽孢杆菌对氨都极其敏感。一种来自碱性泉水的需氧生物（可在pH值高达11.4的环境中生长）更具抗性，但在远低于其生长最高pH值时就对氨表现出毒性反应。在一种生长于接近中性pH值环境中的不明生物体中发现了最强的耐氨性。然而，即便如此，在类木行星上合理预期的氨浓度下，该生物体的存活时间也以小时计。不过，这仍比大肠杆菌的存活时间长两到三个数量级。我们的数据支持这一初步结论：类木行星被能够生长的地球生物污染的可能性不大。然而，所观察到的毒性反应范围，再加上地球上的生命数百万年来未曾接触过高氨浓度这一情况，表明有可能适应更强的耐氨性。
