By Dr David Whitehouse BBC News Online science editor

Some have raised the possibility that terrorists could take publicly available data on harmful microbes and use new genetic engineering techniques to turn the information into lethal bio-weapons.

This frightening prospect has led to calls for the classification of the genome data of harmful organisms.

We have to keep our databases open - to promote research that can increase our level of preparedness Dr Claire Fraser, Tigr

But a leading scientist in the field has told BBC News Online that potential bioterrorists would not be able to manufacture genetically modified killer viruses or bacteria using the databases.

Genome pioneer Dr Claire Fraser, of The Institute for Genomic Research (Tigr), says that although the genetic data of human pathogens is public, no one knows enough to turn this information into bioweapons.

She adds that making genomes secret would merely harm science - just what the terrorists would want.

Science or science fiction?

In 1995, the nerve gas Sarin was released on the Tokyo underground. In 2001, Anthrax was sent in the post in the US, and just a few days ago traces of the poison Ricin were found in a London flat.

All of these substances are frightening and are part of the terrorist's arsenal.

Dr Claire Fraser: Many myths

But some people fear these materials may be mild compared with what terrorists, armed with freely available modern genetic engineering techniques, could do if they produced a self-replicating bioweapon that was infectious and deadly.

A fear of this happening has led to calls that the genomes - genetic blueprints - of some dangerous organisms be classified. But is this the stuff of science fiction, or is it a possibility?

The US National Academies and the Center for Strategic and International Studies has held a conference to discuss the so-called weaponisation of genomes.

Soviet experiments

As well as Dr Claire Fraser, on the panel was George Poste, chair of the US Department of Defense Task Force against Bioterrorism.

He outlined in graphic detail what some fear might happen in the future.

He described tailor-made microbes that produce powerful toxins, evade antibiotics and even produce "stealth viral vectors" that can integrate pathogenic DNA directly into an individual's genome.

Anthrax caused a scare in the US in 2001

Perhaps microbes could be modified to evade detection by diagnostics and by the human immune system. At a later time, these fatal infections could be activated by treatments for other, themselves non-life-threatening, diseases.

Yet still more malevolent microbes might turn the human immune system against itself, causing severe toxic shock, similar to Ebola's biological meltdown.

"These aren't science fiction," said Dr Poste. "The now defunct Soviet bioweapon programme brought many of them to life."

'Debunk the myth'

"In light of these pathogenic possibilities," asked Dr Fraser, "should genome-sequence information be kept under lock and key by government regulation?"

She said it was not an academic question. At Tigr, scientists have sequenced nearly 20 pathogens, including those that cause cholera, pneumonia, anthrax, meningitis, and syphilis.

The institute was also involved in identifying the anthrax strain used in 2001's poison letters.

However, in spite of this, or perhaps because of it, Dr Fraser believes that such DNA sequences should remain public.

Sarin was used in Tokyo in 1995

She told BBC News Online: "I want to debunk the myth that genomics has delivered a fully annotated set of virulence and pathogenicity genes to potential terrorists.

"I have heard some describe genome databases as bioterror catalogues where one could order an antibiotic-resistance gene from organism one, a toxin from organism two, and a cell-adhesion molecule from organism three, and quickly engineer a super pathogen.

"This just isn't the case."

Although scientists have a lot of genetic information about bacteria and viruses that could, in principle, be used to generate superbugs, Dr Fraser said there was so much we did not understand about gene function that such information would be of no practical use to a bioterrorist.

She said the benefits of keeping the data freely available were clear.

"We have to keep our databases open - to promote research that can increase our level of preparedness and as a corollary, perhaps serve as a deterrent."