嗜热和非嗜热Crenarchaeota的生物多样性及演化意义

Crenarchaeota,Euryarchaeata和Korarchaeota组成古菌中3个领域. Euryarchaeota是原核生物中重要的种群,得到了很好的研究,而Crenarchaeota和Korarchaeota直到最近才逐渐受到关注.古菌的生态和演化研究都属于Crenarchaeota领域.一个很重要的观点就是Crenarchaeota的所有独立种群都是极端嗜热的,非嗜热Crenarchaeota目前为止还没有分离出来.嗜热Crenarchaeota主要是在深海热烟囱和陆地热泉中发现的,特征是高温(>80℃)和低pH值(<6).多种嗜热Crenarchaeota化能自养可以利用还原性无机化合物,例如H2和还原性硫.这个特性连同生命树群的深入分支说明生命最后共同的祖先可能是在热液体系中的嗜热自养生物.非嗜热Crenarchaeota和嗜热Crenarchaeota有很近似的系统关系.尽管一般情况下非嗜热Crenarchaeota是不可以培养的,但是其对敞开体系海相、陆相土壤、湖泊和地下的中低温环境的适应性日益增强.这主要取决于独立培养分子学技术的发展,例如16SrRNA基因序列.此外,海洋和土壤中非嗜热Crenarchaeota的研究还表明,非嗜热Crenarchaeota确定组成在碳循环的生物地球化学循环中起着非常重要的作用.

Diversity and Evolutionary Implications of Thermophilic and Non-thermophilic Crenarchaeota

Crenarchaeota are of the three Kingdoms in Archaea with the other two Kingdoms being Euryarchaeota and Korarchaeota. While Euryarchaeota have long been recognized as an important group of the prokaryotes and have been well studied, Crenarchaeota and Korarchaeota have received increasing attention only recently. This review focuses on Crenarchaeota because recent advances in ecological and evolutionary studies of Archaea have mostly occurred in this kingdom. One important observation is that all isolated species of Crenarcheota are extremely thermophilic, whereas non-thermophilic Crenarchaeota have so far resisted attempts of isolation. Thermophilic Crenarchaeota are mostly found in deep sea hydrothermal vents and terrestrial hot springs, which are characterized by growth at high temperature (>80 ℃) and low pH (<6). A variety of thermophilic Crenarchaeota can use reduced inorganic chemicals such as H2 and reduced sulfur for chemoautotrophic growth. This trait, along with the group's deep branching in the tree of life, has lead to the belief that the last common ancestor of life may be a thermophilic autotroph growing in a hydrothermal system. Non-thermophilic Crenarchaeota have a very close phylogenetic relationship to the thermophilic Crenarchaeota. Although currently unculturable, non-thermophilic Crenarchaeota have been increasingly recovered from low- to moderate-temperature environments, which range from open marine to terrestrial soils, lakes, and subsurface. This is largely due to the development of the culture-independent molecular techniques, such as sequencing of the 16S rRNA genes. Furthermore, studies of non-thermophilic Crenarchaeota in oceans and soil suggest that certain members of the non-thermophilic Crenarchaeota may have very important roles in the biogeochemical cycling of carbon.