糖心视频

(糖心视频Org.com) -- A common group of bacteria found in acid bogs and sewage treatment plants has provided scientists with evidence of a 鈥榤issing link鈥� in one of the most important steps in the evolution of life on earth - the emergence of cells with a nucleus containing DNA (eukaryotic cells).

For billions of years, bacteria (single celled organisms without a nucleus) were the only cellular life form on earth. Then, about 1.6 鈥� 2.1 billion years ago, eukaryotic cells emerged. These cells (with a nucleus) heralded the evolution of multi-cellular life on earth including: plants, insects, animals and humans.

Until now scientists have been unable to identify an 鈥榓ncestral cell鈥� linking the early prokaryotes with the later eukaryotes, so fusion theory - where two cells merge to form a new cell 鈥� is often put forward to explain the appearance of these new cell types.

But new findings by scientists from University College Dublin and the European Molecular Biology Laboratory in Heidelberg, Germany, published in the journal Science (26 November 2010), have put paid to the fusion theory explanation, and suggest that an intermediate or 鈥榤issing link鈥� cell did exist all those billions of years ago.

鈥淥ur discovery means that the appearance of eukaryotic cells on earth can be explained by Darwinian evolution over billions of years rather than a 鈥榖ig bang鈥� fusion theory,鈥� says cell biologist Dr Emmanuel Reynaud, from the UCD School of Biology and Environmental Science, University College Dublin, one of the co-authors of the scientific paper.

鈥淥ur analysis shows that PVC [Planctomycetes, Verrucomicrobiae, Chlamydiae] bacteria, members of which are commonly found in today鈥檚 sewage treatment plants or acid bogs, represent an intermediate type of cell structure. They are slightly bigger than other known bacteria, and they also divide more slowly.鈥�

鈥淭he structure of PVC suggests that it is an ancestor of a 鈥榤issing link鈥� cell which connected prokaryotic to eukaryotic cells along an evolutionary path all those billions of years ago,鈥� says Dr Damien P Devos, European Molecular Biology Laboratory, Heidelberg, Germany, the other scientist involved in the findings.