生物谷：一個國際科學(xué)家研究小組近日發(fā)現(xiàn)了年代超過50萬年的活細菌,，這是迄今為止發(fā)現(xiàn)的最為古老的活有機體,。這一發(fā)現(xiàn)將有助于人們更好地理解細胞老化以及探討火星上存在生命的可能性等,。相關(guān)論文發(fā)表在最新一期的《美國國家科學(xué)院院刊》（PNAS）上,。
科學(xué)家知道,，隨著時間的流逝,，所有的細胞最終都會消亡,。但是有些細胞能更好地延遲老化和死亡的過程,，甚至有些有機體還具有再生能力，可以修復(fù)損傷的細胞,。這些有機體及細胞一直是科學(xué)家感興趣的研究對象,。
在最新的研究中，丹麥哥本哈根大學(xué)的Eske Willerslev教授領(lǐng)導(dǎo)他的國際研究小組從加拿大西北部挖掘出的永久凍結(jié)帶（permafrost）中發(fā)現(xiàn)了這種年代超過50萬年的古老細菌,，它是活的,，包含具有活性的DNA。
隨后,，Willerslev和同事從這種細菌的活細胞中分離出了DNA,，并與大容量的基因文庫（gene-bank）中的DNA作了比較，從而準確確定了該種細菌DNA的進化位置,。
Willerslev表示,，此次研究將幫助人們更好地理解細胞分解、延遲老化以及達爾文進化論等問題，并可為有關(guān)火星生命的討論提供一些借鑒,。不過,，要弄清這些細胞長壽的原因以及循環(huán)進化、新舊DNA混合時間等問題,，還需要更深入的研究,。（科學(xué)網(wǎng) 梅進/編譯）
英文原文:
Source: University of Copenhagen
Date: August 28, 2007
World's Oldest Bacteria Found Living In Permafrost
Science Daily — A research team has for the first time ever discovered DNA from living bacteria that are more than half a million years old. Never before has traces of still living organisms that old been found.
The exceptional discovery can lead to a better understanding of the aging of cells and might even cast light on the question of life on Mars. The discovery was made by Professor Eske Willerslev from the University of Copenhagen and his international research team.
All cells decompose with time. But some cells are better than others to postpone the decomposing and thus delay aging and eventually death. And there are even organisms that are capable of regenerate and thereby repair damaged cells. These cells -- their DNA -- are very interesting to the understanding of the process of how cells break down and age.
The research team, which consists of experts in, among other things, DNA traces in sediments and organisms, have found ancient bacteria that still contains active and living DNA. So far, it is the oldest finding of organisms containing active DNA and thus life on this earth. The discovery was made after excavations of layers of permafrost in the north-western Canada, the north-eastern Siberia and Antarctica.
The project is about examining how bacteria can live after having been frozen down for millions of years. Other researchers has tried to uncover the life of the past and the following evolutionary development by focusing on cells that are in a state of dead-like lethargy. "We, on the other hand, have found a method that makes is possible to extract and isolate DNA traces from cells that are still active. It gives a more precise picture of the past life and the evolution towards the present because we are dealing with cells that still have a metabolistic function -- unlike "dead" cells where that function has ceased," says Eske Wilerslev.
Professor Eske Willerslev collecting soil samples in the permafrost in the Yukon, Canada. Researchers found half million year old bacteria in some of the samples collected. (Credit: Duane Froese)
After the fieldwork and the isolation of the DNA, the researchers compared the DNA to DNA from a worldwide gene-bank in the US to identify the ancient material. Much in the same way the police compares fingerprints from a crime, the researchers were able to place the DNA more precisely and to place it in a context.
There is a very long way, of course, from our basic research towards understanding why some cells can become that old. But it is interesting in this context to look at how cells break down and are restored and thus are kept over a very long period. The researchers' methods and results can be used to determine if there was ever life on Mars the way we perceive life on earth.
And then there is the grand perspective in relation to Darwin's evolution theory. It predicts that life never returns to the same genetic level. "But our findings allows us to post the question: are we dealing with a circular evolution where development, so to speak, bites its own tail if and when ancient DNA are mixed with new?" says Eske Willerslev.
The discovery is being published in the current issue of PNAS (Proceedings of The National Academy of Sciences).
Note: This story has been adapted from a news release issued by University of Copenhagen.
