A giant virus found in a Bradford cooling tower and stored in a Shipley scientist's freezer for years has sparked a global debate on the origins of life.

Researchers have just finished mapping the genetic blueprint of "Mimivirus" and the results have caused a furore among the world's foremost scientists.

They recently discovered Mimivirus was several times larger than any other virus - and bigger than many bacteria.

Now scientists are starting to question why a virus would need to be so big - with some believing it forces us to question the origin and evolution of life itself.

Shipley microbiologist Dr Tim Rowbotham, 56, was working for Leeds Public Health Laboratory in 1992, when he first found unusual material in a small industrial cooling tower during a Legionnaires' disease scare in Bradford.

He named the infected cells Bradford coccus and saved them in his freezer for six years before sending them to French researchers on his retirement.

Now working as an ironmonger, Dr Rowbotham said: "The Mimivirus is a giant virus which people are now thinking could be a new branch on the tree of life. This currently leads from virus to bacteria to plant to animal.

"It is so unusual because it is more than a virus but less than a bacteria."

One of the defining characteristics of viruses is that they cannot make proteins independently. Instead they have to harness the genes of the host they infect.

But, mysteriously, Mimivirus contains a number of genes for protein translation. It also features genes for DNA repair enzymes, "heat shock" proteins that respond to stress and trademarks of cellular life.

In all, about half of Mimivirus's genes are new to science. In another viral first, Mimivirus boasts some genes from the "universal core genome", the 60 or so genes common to every bacterium, plant and animal that has been sequenced.

Scientists, led by Didier Raoult of the CNRS research facility at the University of the Mediterranean in Marseilles, wrote in the journal Science: "The size and complexity of the Mimivirus genome challenges the established frontier between viruses and parasitic cellular organisms."

A second American scientist added: "Mimivirus breaks the boundary that used to be considered sacred - the boundary between viruses and cellular life forms."

Molecular evolutionist Jean-Michel Claverie, also based at the University of the Mediterranean, has gone even further.

He believes Mimivirus is growing and should be categorised not as a DNA virus, but as a "girus" - or giant virus.

Controversially, Claverie thinks giruses should be placed outside the three established domains of life - bacteria, archaea and eukaryotes.

In layman's terms, that could make it a pre-cursor to all life on earth - not bad for a bug from Bradford!

Dr Rowbotham admits to feeling a little envious of the scientists now breaking new ground with the viral beast he discovered.

"It does make me a little envious that I am not working with the French to isolate it," he added.

"I knew it was something special. I had never seen anything like it before.

"I gave it to the French so they could continue the work and they have done a great job."

Since Mimivirus was found, scientists have undertaken pioneering research in laboratories around the world to see if known viruses have any other surprises waiting to be discovered.