Study of marine DNA finds new branches on the tree of life


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It seems the debate about the possibility of a fourth domain of life refuses to die down, with a US scientist claiming to have discovered a whole new branch of the tree of life. Living things are currently split into three domains — eukaryotes or complex-celled organisms like animals, plants and humans; bacteria; and archaea, the last two being simple- celled microorganisms.

Microbial life in a sample of seawater. The geneticist Craig Venter claims to have found a whole new domain of life in a similar sample [Credit: PA]

Now, Professor Jonathan Eisen, an evolutionary biologist at the University of California, claims he may have discovered a fourth.

He has used complicated gene sequencing techniques to look at DNA collected by maverick researcher Dr Craig Venter on a round the world yachting trip. He found that some of the genes did not fit into the three domains and that he could possibly have stumbled on a whole new domain.

Trying to classify the new DNA has proved impossible and so Prof Eisen has published his findings in the ‘Public Library of Science’ journal in the hope others can help.

“The question is, what are they from? They could represent an unusual virus, which is interesting enough. More interestingly still, they could represent a totally new branch in the tree of life.

“Even though we did not have the story completely pinned down, we decided to finally write up the paper to get other people to think about this issue,” Prof Eisen was quoted by ‘The Daily Telegraph’ as saying.

One of the difficulties of trying to study novel genes is that it is hard to culture them to such a quantity to make them easily readable. But Prof Eisen used methods honed by Dr Venter in his successful attempt to read human genetic code.

They have dubbed the technique as “metagenomics” and it involves breaking down the DNA to sizeable chunks, decoding them and then reassembling in the correct order. The science benefits greatly from ever more powerful and cheaper computers. The team applied the technique to seawater samples collected between 2003 and 2007 from the world’s oceans by Dr Venter on his yacht, Sorcerer II.

Prof Eisen stumbled on variations of two genes called RecA and RpoB, both of which are old and abundant, which had different characteristics to anything in the public genetic databases.

Research into classifying the findings go on but one of the problems is that it is not known where the genes come from — they’re simply taken from samples of seawater. 

Source: Deccan Herald [April 05, 2011]


  1. I am thrilled to have the press covering some details of my recent work (I am the senior author on the paper that is being discussed). There are a few things in this story that are a bit inaccurate and I am writing here to clarify some details.

    1. We actually did not claim to find a new domain of life as the headline suggests. The main article here is more accurate (perhaps the headline was written by someone other than the author of this article). What we said in our paper was that there were many possible explanations for the unusual bits of DNA that we found – and that a new domain of life was one of what we thought were two plausible explanations. We said a another (and possibly more likely) explanation is that the unusual pieces of DNA we found came from previously uncharacterized viruses. (Viruses are currently not considered by most scientists to be true organisms and thus are not normally places onto the "Tree of Life).

    2. We did not invent the metagenomics method that we used. This has been developed by many people and we did not invent the name either. However, Venter (my collaborator) did do the first large scale metagenomic study which was in part where the data we used came from.

    3. We did not stumble upon the unusual RecA and RpoB genes. The whole point of our study is that we set out to see if we could find unusual RecA or RpoB genes … We did a lot of stumbling mind you in the course of this project but not in that aspect.

    Jonathan Eisen
    Prof. University of California, Davis, USA



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