- A strange life form has been identified in Bradford.
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- Genetic analysis reveals that the organism is so bizarre
and unlike anything else seen by scientists that perhaps it should be placed
in its own category of living things.
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- The creature, first discovered in a small industrial
cooling tower on the outskirts of the city, could qualify for a new "domain"
in the tree of life - where a domain is a bigger category than a kingdom
or a phylum.
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- The "giant virus", dubbed the Mimivirus, or
"mimicking microbe", because it was first mistaken for a bacterium,
inhabits amoebae and is more than twice as big as any other virus so far
found. At about half a millionth of a metre across - around the size of
a small bacterium - it is one of the few that can be seen under a light
microscope.
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- Two research teams in the Marseille School of Medicine,
led by Prof Didier Raoult and Prof Jean-Michel Claverie, have "read"
the genetic code of the organism and found a number of genes previously
thought to belong only to more complex life forms.
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- The size and complexity of the Mimivirus genetic code
- which is 1.2 million "letters" long, at least 10 times larger
than the code of a typical virus - "challenges the established frontier
between viruses and parasitic cellular organisms", they report today
in the journal Science.
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- One of the defining characteristics of a virus is that
it is unable to make proteins independently, instead relying on the cells
it infects to manufacture its proteins and thus reproduce. But the Mimivirus
contains a number of genes for protein translation.
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- It also contains genes for DNA repair enzymes and other
proteins, all typically thought to be trademarks of cellular organisms.
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- The Mimivirus - which so far has only been found in Bradford
- appears to represent a new family of "nucleocytoplasmic" large
DNA viruses that emerged with the first life on Earth some four billion
years ago, said Prof Raoult. After much debate among his team, "for
the first time we have enough genetic information to conclude that there
is a fourth domain of life", he said. "If this is true, this
is revolutionary."
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- The other three domains of life are the eukaryotes, which
have cells that contain a nucleus, and the prokaryotes, unicellular organisms
that are divided into the bacteria and archaea.
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- The family tree drawn up by Prof Claverie shows that
the Mimivirus is no more related to the eukaryotes as it is to bacteria.
'This organism is as old as all the rest of living organisms," he
said.
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- However, Dr Dave Roberts, head of microbiology at the
Natural History Museum, London, was "deeply sceptical" that the
Mimivirus deserves to be placed in its own domain, though he agreed that
it did mark a new family.
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- "There are a lots of odd things turning up in the
microbial world all the time," he said.
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- "It is a fascinating paper and very exciting. The
virus seems to link to a group prior to the appearance of the three domains
we currently recognise. But we are not convinced that the tree of life
is still a branching structure when you get that deep."
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- The giant virus has not so far been linked with disease.
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- © Copyright of Telegraph Group Limited 2004. http://www.telegraph.co.uk/news/main.jhtml?xml=/news/20
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