Bowers Karen J, Mesbah Noha M, Wiegel Juergen
Department of Microbiology, University of Georgia, Athens, GA, USA.
Saline Syst. 2009 Nov 23;5:9. doi: 10.1186/1746-1448-5-9.
Bacterial microorganisms that grow optimally at Na+ concentrations of 1.7 M, or the equivalent of 10% (w/v) NaCl, and greater are considered to be extreme halophiles. This review focuses on the correlation between the extent of alkaline pH and elevated temperature optima and the extent of salt tolerance of extremely halophilic eubacteria; the focus is on those with alkaline pH optima, above 8.5, and elevated temperature optima, above 50 degrees C. If all three conditions are required for optimal growth, these microorganisms are termed "poly-extremophiles". However, only a very few extreme halophiles able to grow optimally under alkaline conditions as well as at elevated temperatures have been isolated so far. Therefore the question is: do the combined extreme growth conditions of the recently isolated poly-extremophiles, i.e., anaerobic halophilic alkalithermophiles, approach a physico-chemical boundary for life? These poly-extremophiles are of interest, as their adaptive mechanisms give insight into organisms' abilities to survive in environments which were previously considered prohibitive to life, as well as to possible properties of early evolutionary and extraterrestrial life forms.
在1.7M Na+浓度（相当于10%（w/v）NaCl）及更高浓度下生长最佳的细菌微生物被认为是极端嗜盐菌。本综述重点关注碱性pH值范围和最佳温度升高程度与极端嗜盐真细菌耐盐程度之间的相关性；重点关注那些最佳pH值高于8.5且最佳温度高于50摄氏度的嗜盐菌。如果最佳生长需要所有这三个条件，这些微生物就被称为“多极端嗜极菌”。然而，到目前为止，仅分离出极少数能够在碱性条件以及高温下最佳生长的极端嗜盐菌。因此问题是：最近分离出的多极端嗜极菌，即厌氧嗜盐碱热菌，其组合的极端生长条件是否接近生命的物理化学边界？这些多极端嗜极菌很有趣，因为它们的适应机制有助于深入了解生物体在以前被认为不适宜生命存在的环境中生存的能力，以及早期进化和外星生命形式的可能特性。
