Microbes are widely assumed to be capable of colonizing even the most challenging terrestrial surface environments on Earth given enough time. We would not expect to find surface soils uninhabited by microbes as soils typically harbor diverse microbial communities and viable microbes have been detected in soils exposed to even the most inhospitable conditions. However, if uninhabited soils do exist, we might expect to find them in Antarctica. We analyzed 204 ice-free soils collected from across a remote valley in the Transantarctic Mountains (84–85°S, 174–177°W) and were able to identify a potential limit of microbial habitability. While most of the soils we tested contained diverse microbial communities, with fungi being particularly ubiquitous, microbes could not be detected in many of the driest, higher elevation soils—results that were confirmed using cultivation-dependent, cultivation-independent, and metabolic assays. While we cannot confirm that this subset of soils is completely sterile and devoid of microbial life, our results suggest that microbial life is severely restricted in the coldest, driest, and saltiest Antarctic soils. Constant exposure to these conditions for thousands of years has limited microbial communities so that their presence and activity is below detectable limits using a variety of standard methods. Such soils are unlikely to be unique to the studied region with this work supporting previous hypotheses that microbial habitability is constrained by near-continuous exposure to cold, dry, and salty conditions, establishing the environmental conditions that limit microbial life in terrestrial surface soils.

中文翻译：

---

探索土壤中微生物宜居性的边界

人们普遍认为，只要有足够的时间，微生物甚至能够在地球上最具挑战性的陆地表面环境中定居。我们不希望找到没有微生物栖息的表层土壤，因为土壤通常含有多种微生物群落，并且在暴露于最恶劣条件的土壤中也检测到了活微生物。然而，如果无人居住的土壤确实存在，我们可能希望在南极洲找到它们。我们分析了从横贯南极山脉（84-85°S，174-177°W）的偏远山谷收集的 204 种无冰土壤，并能够确定微生物宜居性的潜在限制。虽然我们测试的大多数土壤都含有不同的微生物群落，真菌尤其普遍存在，但在许多最干燥的土壤中无法检测到微生物，高海拔土壤——使用依赖栽培、不依赖栽培和代谢测定法证实的结果。虽然我们无法确认这部分土壤是完全无菌的并且没有微生物生命，但我们的结果表明，微生物生命在最冷、最干燥和最咸的南极土壤中受到严重限制。数千年来持续暴露于这些条件限制了微生物群落，因此它们的存在和活动低于使用各种标准方法可检测到的限度。这种土壤不太可能是研究区域所独有的，这项工作支持了之前的假设，即微生物的宜居性受到近乎连续暴露于寒冷、干燥和咸条件的限制，从而建立了限制陆地表层土壤微生物生命的环境条件。