Tolerance limits of methanogenic life in terrestrial permafrost

地球上生命的进化早在3.8亿年前就开始了，当时火星上的生活条件与早期地球上的生活条件相似。假设两颗行星上的最初生命都是由复杂的微生物群落决定的，那么火星上的生命必须适应急剧变化的环境条件，否则就会再次灭绝。火星原始生命存活的一种可能是地下岩石自养生态系统。类似的环境存在于地球上的永久冻土区。因此，陆地永久冻土被认为是地外模拟研究的一个模型。计划项目的主要目的是研究来自西伯利亚永久冻土的岩石自养微生物的容忍极限。除了表现出各种适应策略的硝化细菌外，主要是产甲烷的古细菌，它们对早期地球的氧气和有机自由环境表现出特定的适应。微生物在自然土壤和纯细菌培养物中的耐受性将根据不同的胁迫因素进行测试。将分析受极端温度、干燥、饥饿和盐浓度增加影响的生长边界。比较系统研究将有助于了解现代火星冰冻圈和其他地外永久冻土栖息地。这些知识是搜索和了解地外生命的重要基础，如果存在的话，特别是关于目前火星上可能受保护的壁龛。

The evolution of life on Earth had already started 3.8 Ga ago, when living conditions on Mars were similar to those on early Earth. Assuming that first life on both planets was determined by complex microbial communities, the Martian life must have adapted to drastically changing environmental conditions or become extinct again. One possibility for survival of Martian primitive life might be subsurface lithoautotrophic ecosystems. Comparable environments exist in permafrost regions on Earth. Thus, terrestrial permafrost is considered to be a model for extraterrestrial analogue studies. The main objective of the planed project is to study tolerance limits of lithoautotrophic microorganisms derived from Siberian permafrost. Beside nitrifying bacteria, which show various adaptation strategies, primarily methanogenic archaea will be used, which show specific adaptations to the oxygen and organic free environment of early Earth. Tolerances of microbes within natural soils as well as pure bacterial cultures will be tested with regard to different stress factors. The borders of growth influenced by temperature extremes, desiccation, starvation and increased salt concentrations will be analyzed. The comparative system studies will serve to understand the modern Mars cryosphere and other extraterrestrial permafrost habitats. This knowledge represents an essential basis for searching and understanding of extraterrestrial life, if present, especially concerning possible protected niches on present Mars.