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Wednesday, 2 August, 2000, 19:20 GMT 20:20 UK
Cholera's genetic secrets revealed
Vibrio cholerae bacterium
Vibrio cholerae: Responsible for the deaths of millions
By BBC News Online science editor Dr David Whitehouse

Scientists have decoded the genome of the bacterium Vibrio cholerae, the cause of cholera.

Millions around the world have died because of this microbe. Cholera has been epidemic in southern Asia for over 2,000 years and has spawned seven global pandemics, the last one being in 1911.

It is hoped that the detailed genetic information now available will allow new treatments and vaccines to be developed.

The completed sequence is published in the journal Nature.

Severe diarrhoea

Vibrio cholerae is found in drinking water contaminated with human faeces. The bacterium attacks the gut and patients suffer severe diarrhoea. This leads to a rapid loss of fluid and important body chemicals.

Death can occur as quickly as a few hours after the onset of symptoms. The mortality rate is more than 50% in untreated cases, but falls to less than 1% with proper treatment.

A simple cocktail of electrolytes and water will save the vast majority of sufferers if given soon enough.

In London, in 1854, the physician John Snow traced an outbreak to a water pump in Broad Street. He sealed the well and the outbreak ceased thereby proving that cholera was spread by an infectious agent.

But it was not until 1883 that the German physician and bacteriologist Robert Koch identified Vibrio cholerae as the culprit.

Salt-water estuaries

Decoding the bacterium's genome should aid the development of new vaccines and medicines that can be used against the disease.

Knowledge of the genome may also help scientists understand how the organism can switch lifestyles; it lives in salt-water estuaries between epidemics.

Jennie Hunter-Cevera, president of University of Maryland Biotechnology Institute (UMBI), said: "The sequence provides a molecular window into understanding the life cycle of a bacterium that is naturally occurring in the aquatic environment, and yet often plays havoc as a human pathogen."

V. cholerae DNA is split between two circular chromosomes with one holding about three times more of the double-stranded molecule than the other. Researchers speculate that the smaller chromosome may originally have been a free-living organism that was somehow captured.

The organism's genetic code has a total of 4,033,460 DNA base pairs, or "letters". The vast majority of recognisable genes for cell functions and toxicity are found on the large chromosome.

Smaller chromosome

The smaller chromosome contains many genes that have come from other organisms distantly related to V. cholerae. Since it was captured, important genes from the larger chromosome have "jumped" on to the smaller one making this structure essential for the organism's survival.

Scientists have described the detailed genetic information now available for the organism as a treasure-trove for how a cell divides responsibility between two chromosomes.

Dr Claire Fraser, President of The Institute for Genomic Research (Tigr), said: "The determination of the V. cholerae genome sequence represents a milestone in the history of cholera research.

"This information has begun to provide insights into how a free-living environmental organism has emerged to become a human pathogen and it will greatly accelerate our understanding of the disease and its control."

Scientists from several institutions were involved in the research: Tigr, UMBI, University of Maryland-College Park and the Harvard Medical School.

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See also:

10 May 00 | Sci/Tech
Danger bacterium decoded in a day
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Deadly bugs decoded
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The history of genetics
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