NASA John F. Kennedy Space Center , Surface Systems Office, Kennedy Space Center, Florida.
Astrobiology. 2013 Oct;13(10):981-90. doi: 10.1089/ast.2013.1074. Epub 2013 Oct 9.
Microbial taxa from every major biological lineage have been detected in Earth's upper atmosphere. The goal of this review is to communicate (1) relevant astrobiology questions that can be addressed with upper atmosphere microbiology studies and (2) available sampling methods for collecting microbes at extreme altitudes. Precipitation, mountain stations, airplanes, balloons, rockets, and satellites are all feasible routes for conducting aerobiology research. However, more efficient air samplers are needed, and contamination is also a pervasive problem in the field. Measuring microbial signatures without false positives in the upper atmosphere might contribute to sterilization and bioburden reduction methods for proposed astrobiology missions. Intriguingly, environmental conditions in the upper atmosphere resemble the surface conditions of Mars (extreme cold, hypobaria, desiccation, and irradiation). Whether terrestrial microbes are active in the upper atmosphere is an area of intense research interest. If, in fact, microbial metabolism, growth, or replication is achievable independent of Earth's surface, then the search for habitable zones on other worlds should be broadened to include atmospheres (e.g., the high-altitude clouds of Venus). Furthermore, viable cells in the heavily irradiated upper atmosphere of Earth could help identify microbial genes or enzymes that bestow radiation resistance. Compelling astrobiology questions on the origin of life (if the atmosphere synthesized organic aerosols), evolution (if airborne transport influenced microbial mutation rates and speciation), and panspermia (outbound or inbound) are also testable in Earth's upper atmosphere.
从每个主要生物谱系中都检测到了地球高层大气中的微生物类群。本综述的目的是交流（1）可以通过高层大气微生物学研究解决的相关天体生物学问题，以及（2）在极端海拔收集微生物的可用采样方法。降水、山区站、飞机、气球、火箭和卫星都是进行空气生物学研究的可行途径。然而，需要更有效的空气采样器，而且污染也是该领域普遍存在的问题。在高层大气中测量微生物特征而不出现假阳性可能有助于为拟议的天体生物学任务提供灭菌和生物负荷降低方法。有趣的是，高层大气的环境条件类似于火星的表面条件（极冷、低气压、干燥和辐射）。陆地微生物是否在高层大气中活跃是一个研究兴趣浓厚的领域。如果事实上微生物的代谢、生长或复制可以独立于地球表面进行，那么在其他星球上寻找宜居带的范围应该扩大到包括大气层（例如，金星的高空云层）。此外，地球强辐射高层大气中的存活细胞可以帮助确定赋予辐射抗性的微生物基因或酶。有关生命起源（如果大气合成有机气溶胶）、进化（如果空气传播影响微生物突变率和物种形成）和泛种论（向外或向内）的引人注目的天体生物学问题也可以在地球高层大气中进行测试。
