Hopton Cassie M, Nienow Peter, Cockell Charles S
UK Centre for Astrobiology, School of Physics and Astronomy, University of Edinburgh, James Clerk Maxwell Building, Peter Guthrie Tait Road, Edinburgh, EH9 3FD, UK.
School of Geosciences, University of Edinburgh, Drummond St, Edinburgh, EH8 9XP, UK.
Sci Rep. 2025 Jun 4;15(1):19549. doi: 10.1038/s41598-025-03858-z.
The subsurface oceans of icy moons, expected to retain appreciable concentrations of ammonia, are of significant interest to astrobiology. On Earth, ammonia is released in large quantities, primarily through anthropogenic activities. Ammonia is toxic to many forms of life at high concentrations, and thus it is necessary to understand the habitability impact of ammonia on these environments. The survival limits and physiological response of aerobic bacteria in ammonia, and whether ammonia toxicity is distinct from toxicity by high pH, is poorly understood. Here, we investigate the survival thresholds, growth kinetics, and metabolomic response of Halomonas meridiana in ammonia-water solutions and pH-matched sodium hydroxide solutions. Using closed- and open-air systems to mimic environments with NH retention or dispersion, we found complete and partial cell death above 0.05 M ammonia, respectively. In open-air systems, a sub-set of cells survived up to 0.25 M ammonia; metabolomics revealed unique physiological responses to ammonia, including elevation of cyclic compounds and Coenzyme A metabolites, suggesting mechanisms of ammonia toxicity and adaptation. Ammonia and high pH toxicity were found to be distinct. These findings show that ammonia can impose a distinct geobiological limit, potentially constraining the habitability of ammonia-rich terrestrial and extraterrestrial environments.
冰卫星的地下海洋有望保留可观浓度的氨，这对天体生物学具有重大意义。在地球上，氨主要通过人为活动大量释放。高浓度的氨对多种生命形式有毒，因此有必要了解氨对这些环境宜居性的影响。人们对需氧细菌在氨中的生存极限和生理反应，以及氨毒性是否与高pH值毒性不同知之甚少。在此，我们研究了嗜盐嗜碱菌在氨水溶液和pH值匹配的氢氧化钠溶液中的生存阈值、生长动力学和代谢组学反应。使用封闭和开放空气系统模拟氨保留或扩散的环境，我们分别发现氨浓度高于0.05 M时细胞完全死亡和部分死亡。在开放空气系统中，一部分细胞在高达0.25 M的氨浓度下存活；代谢组学揭示了对氨的独特生理反应，包括环状化合物和辅酶A代谢物的升高，这表明了氨毒性和适应性的机制。研究发现氨毒性和高pH值毒性是不同的。这些发现表明，氨可能会施加一个独特的地球生物学限制，潜在地限制富含氨的地球和外星环境的宜居性。
