By Paul Rincon
BBC News science reporter
Experts have deciphered the complete DNA sequence for one of the most infectious germs known to science.
Just 10 of the bacteria can cause disease in humans
The Francisella tularensis bacterium is a candidate bioterror weapon, as it takes just 10 microbes to bring on disease in humans.
The genome sequencing work is already speeding up the search for a vaccine against the potentially deadly bug.
An international team, including UK Ministry of Defence scientists, report their findings in Nature Genetics.
"There aren't any [other pathogens] I can think of that are more infectious," said co-author Professor Richard Titball, of the Defence Science and Technology Laboratory (DSTL) at Porton Down, UK.
"There are a couple that are in the same ballpark and they are also candidate bioweapons."
The bacterium causes a disease called tularemia - or "rabbit fever" - in humans and animals. It is high on the watch-list of biological agents experts fear might be used in terror attacks.
"Until recently, there wouldn't have been much interest in terms of UK public health because [F. tularensis] doesn't cause many cases of disease in the British population," said Professor Bill Keevil, a microbiologist at the University of Southampton, UK.
"But obviously, with the terrorism angle, there's more interest now."
Natural cases of tularemia occur across North America, Europe and Asia. Humans can catch the disease either from tick, fly and mosquito bites or by inhaling airborne particles (aerosols).
One outbreak in Martha's Vineyard, US, in 2000 was probably triggered by someone running over a rabbit carcass while mowing a lawn. The airborne bacteria infected two people.
On guard: Tularemia is a candidate bioweapon
The World Health Organization estimates that airborne dispersal of 50kg of F. tularensis over an urban area with 5 million inhabitants would kill 19,000 people and incapacitate a further 250,000.
"Even people who don't die are chronically sick for weeks or months. This is a disease that makes you really ill," Professor Titball told the BBC News website.
It is hoped the sequencing work, which took five years to complete, will kickstart a worldwide bio-defence programme for F. tularensis, leading to the development of new vaccines and diagnostic tools.
The researchers from UK, US and Swedish institutes say they have already picked out protein targets useful for creating a vaccine.
They also found an unusual cluster of genes thought to be involved in causing illness.
Intriguingly, these genes have never been seen in another living organism. Scientists do not yet know how F. tularensis acquired them or how they work.
But according to Professor Titball, their presence may suggest the microbe has hitherto unknown ways of causing disease.
Did the Soviets use tularemia at the battle of Stalingrad?
Tularemia was first described as a plague-like disease of rodents in 1911 and as a potentially fatal disease in humans shortly afterwards.
The Japanese were first to study its candidacy as a germ warfare agent, in a programme lasting from 1932 to 1945.
Ken Alibek, a former Soviet bioweapons scientist, has suggested the Red Army may have used tularemia deliberately against German forces on the eastern European front during World War II - but the outbreak could also have been entirely natural.
The US military weaponised the bacterium during the 1950s and 1960s. A parallel Soviet effort allegedly continued into the early 1990s. It is not known whether former states of the USSR continue to hold stocks.