Mesbah Noha M, Wiegel Juergen
Department of Microbiology, University of Georgia, Athens, GA 30602-2605, USA.
Ann N Y Acad Sci. 2008 Mar;1125:44-57. doi: 10.1196/annals.1419.028.
The ability of anaerobic microorganisms to proliferate under extreme conditions is of widespread importance for microbial physiology, remediation, industry, and evolution. The halophilic alkalithermophiles are a novel group of polyextremophiles. Tolerance to alkaline pH, elevated NaCl concentrations, and high temperatures necessitates mechanisms for cytoplasmic pH acidification; permeability control of the cell membrane; and stability of proteins, the cell wall, and other cellular constituents to multiple extreme conditions. Although it is generally assumed that extremophiles growing at more than one extreme combine adaptive mechanisms for each individual extreme, adaptations for individual extremes often counteract each other. However, in alkaline, hypersaline niches heated via intense solar irradiation, culture-independent analyses have revealed the presence of an extensive diversity of aerobic and anaerobic microorganisms belonging to Bacteria and Archaea that survive and grow under multiple harsh conditions. Thus, polyextremophiles must have developed novel adaptive strategies enabling them to grow and proliferate under multiple extreme conditions. The recent isolation of two novel anaerobic, halophilic alkalithermophiles, Natranaerobius thermophilus and Halonatronum saccharophilum, will provide a platform for detailed biochemical, genomic, and proteomic experiments, allowing a greater understanding of the novel adaptive mechanisms undoubtedly employed by polyextremophiles. In this review, we highlight growth characteristics, ecology, and phylogeny of the anaerobic halophilic alkalithermophiles isolated. We also describe the bioenergetic and physiological problems posed by growth at the multiple extreme conditions of alkaline pH, high NaCl concentration, and elevated temperature under anoxic conditions and highlight recent findings and unresolved problems regarding adaptation to multiple extreme conditions.
厌氧微生物在极端条件下增殖的能力对于微生物生理学、修复、工业和进化具有广泛的重要性。嗜盐嗜碱嗜热菌是一类新型的多极端嗜极菌。耐受碱性pH值、升高的NaCl浓度和高温需要细胞质pH值酸化的机制；细胞膜的通透性控制；以及蛋白质、细胞壁和其他细胞成分在多种极端条件下的稳定性。虽然通常认为在多个极端条件下生长的嗜极菌结合了针对每个单独极端条件的适应机制，但针对单个极端条件的适应往往会相互抵消。然而，在通过强烈太阳辐射加热的碱性、高盐生态位中，不依赖培养的分析揭示了存在广泛多样的属于细菌和古菌的需氧和厌氧微生物，它们在多种恶劣条件下生存和生长。因此，多极端嗜极菌必定已经发展出了新颖的适应策略，使它们能够在多种极端条件下生长和增殖。最近分离出的两种新型厌氧嗜盐嗜碱嗜热菌，嗜热嗜盐碱厌氧菌和嗜糖嗜盐碱杆菌，将为详细的生化、基因组和蛋白质组实验提供一个平台，从而能够更深入地了解多极端嗜极菌无疑采用的新型适应机制。在这篇综述中，我们重点介绍了已分离出的厌氧嗜盐嗜碱嗜热菌的生长特性、生态学和系统发育。我们还描述了在碱性pH值、高NaCl浓度和缺氧条件下的高温等多种极端条件下生长所带来的生物能量和生理问题，并重点介绍了关于适应多种极端条件的最新发现和未解决的问题。
