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Fourth variety of life found by US scientist

world Updated: Apr 06, 2011 01:19 IST

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.

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.

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.