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Genome of bacterium that causes leprosy is sequenced
By Bijal P. Trivedi

French and British researchers have sequenced the genome of Mycobacterium leprae, the bacterium that causes leprosy. The genome sequence will be used to investigate new ways to treat, diagnose and detect the disease, which often does not produce symptoms until one year after the infection.

Generating enough bacteria for the project was a technical achievement. The bacterium grows particularly slowly—it takes almost 14 days to split into two cells. M. leprae also requires a unique environment in which to grow: The researchers grew large amounts of the bacterium in an armadillo.

M. leprae is a close relative of Mycobacterium tuberculosis. In fact, the two pathogens share about 90 percent of the same genes. A surprise of the research is that M. leprae has experienced extensive gene loss. Only about half of the bacterium's genome contains functional genes. Compared to M. tuberculosis, which has almost 4,000 genes, M. leprae has only about 1,600 active genes. The rest of the genome appears to be cluttered with more than 1,100 'pseudogenes,' which resemble genes in M. tuberculosis but are no longer active.

The researchers believe that one reason the bacterium is so difficult to cultivate in the laboratory is that it has lost genes controlling many important metabolic pathways.

There are close to 700,000 new cases of leprosy reported each year. Most cases of the disease are found in India, Africa and South America.

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Cole, S.T. et al. Massive gene decay in the leprosy bacillus. Nature 409, 1007-1011 (February 22, 2001).

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