科學(xué)家認(rèn)為,，地球上的所有生物———從人類到細(xì)菌，從藍(lán)鈴花到藍(lán)鯨———都源自同一種實(shí)體,，一種30億年或40億年前漂浮在“原始湯”周圍的原胞,。這種實(shí)體是什么樣子呢？它又是如何生活,，以及生活在哪里呢,？在最新一期Nature上面，法國(guó)的科學(xué)家為我們揭開(kāi)了謎團(tuán),。
這種實(shí)體被稱為“露卡(LUCA)”,，也就是“第一個(gè)基本的共同祖先”之意，它沒(méi)有留下任何已知的化石,，也沒(méi)有其他物理線索可揭示其身份,，所以尋找“LUCA”的人們依靠間接證據(jù)來(lái)獲取關(guān)于“LUCA”的生物信息及環(huán)境信息。
根據(jù)來(lái)自現(xiàn)存基因組的基因證據(jù)對(duì)先祖蛋白序列所做重建表明,，“LUCA”所處環(huán)境很熱,，“LUCA”是嗜熱生物。但核糖體RNA（rRNA）序列過(guò)去被認(rèn)為與一個(gè)溫度較低的環(huán)境相一致,。一種新的“分子溫度計(jì)”方法可能已經(jīng)解決了這一明顯的偏差,。利用關(guān)于分子演化的最新數(shù)學(xué)模型對(duì)來(lái)自數(shù)百種現(xiàn)代物種的rRNA及蛋白序列所做分析表明，存在兩個(gè)環(huán)境溫度變化階段,。后來(lái)變成“LUCA”的生物先是嗜中溫的,，生活在大約60°C的水中,，然后適應(yīng)了較高的溫度（高于70°C），產(chǎn)生了一個(gè)嗜熱的共同祖先,。隨著之后海洋溫度降低,，細(xì)菌（Bacteria）和古細(xì)菌-真核生物（Archaea-Eukaryota）發(fā)生分化,。（生物谷Bioon.com）
生物谷推薦原始出處：
Nature 456, 942-945 (18 December 2008) | doi:10.1038/nature07393
Parallel adaptations to high temperatures in the Archaean eon
Bastien Boussau1,3, Samuel Blanquart2,3, Anamaria Necsulea1, Nicolas Lartillot2,4 & Manolo Gouy1
1 Laboratoire de Biométrie et Biologie Evolutive, CNRS, Université de Lyon, Université Lyon I, 43 Boulevard du 11 Novembre, 69622 Villeurbanne, France
2 LIRMM, CNRS, 161 rue Ada, 34392 Montpellier, France
3 These authors contributed equally to this work.
4 Present address: Département de Biochimie, Université de Montréal, C.P. 6128, succursale Centre-Ville, Montréal QC H3C3J7, Canada.
Fossils of organisms dating from the origin and diversification of cellular life are scant and difficult to interpret1, for this reason alternative means to investigate the ecology of the last universal common ancestor (LUCA) and of the ancestors of the three domains of life are of great scientific value. It was recently recognized that the effects of temperature on ancestral organisms left 'genetic footprints' that could be uncovered in extant genomes2, 3, 4. Accordingly, analyses of resurrected proteins predicted that the bacterial ancestor was thermophilic and that Bacteria subsequently adapted to lower temperatures3, 4. As the archaeal ancestor is also thought to have been thermophilic5, the LUCA was parsimoniously inferred as thermophilic too. However, an analysis of ribosomal RNAs supported the hypothesis of a non-hyperthermophilic LUCA2. Here we show that both rRNA and protein sequences analysed with advanced, realistic models of molecular evolution6, 7 provide independent support for two environmental-temperature-related phases during the evolutionary history of the tree of life. In the first period, thermotolerance increased from a mesophilic LUCA to thermophilic ancestors of Bacteria and of Archaea–Eukaryota; in the second period, it decreased. Therefore, the two lineages descending from the LUCA and leading to the ancestors of Bacteria and Archaea–Eukaryota convergently adapted to high temperatures, possibly in response to a climate change of the early Earth1, 8, 9, and/or aided by the transition from an RNA genome in the LUCA to organisms with more thermostable DNA genomes10, 11. This analysis unifies apparently contradictory results2, 3, 4 into a coherent depiction of the evolution of an ecological trait over the entire tree of life.
