Scientists crack genome of plague bacteria

By Our Science Correspondent

THIRUVANANTHAPURAM, OCT. 4. The secret of one of humanity's great scourges, plague, is now likely to be laid bare. British scientists have sequenced the genome of yersinia pestis, the bacterium which causes the disease.

In the 14th century, the `Black Death' swept through Asia, Africa and Europe, taking some 50 million lives. In India, the plague is believed to have caused six million deaths between 1898 and 1908. India had major plague outbreaks in 1954, 1963 and most recently in 1994.

According to the World Health Organisation, six countries have been reporting cases of plague virtually every year for the past four decades. There have also been fears that the plague bacterium might be used in germ warfare.

Now that the British researchers have sequenced the entire genome of yersinia pestis, the hope is that the secrets of its virulence as well as its evolution can be better understood.

The yersinia pestis is primarily a rodent pathogen, with a predilection for rats. But it is able to use fleas to move from rat to rat and also to start the cycle of infection in humans. Once a person is infected, the bacterium travels to the lungs and can then spread through droplets spewed out when the affected person coughs.

In a paper published in the latest issue of the journal, Nature, scientists involved in the sequencing effort pointed out that this pathogen, which was highly virulent in humans and caused fatal diseases, had evolved from bacteria which caused non-fatal intestinal disease. The study of the yersinia pestis genome could therefore provide ``a unique insight'' into how new and virulent pathogens evolved.

The yersinia pestis is closely related to yersinia pseudotuberculosis which infects the alimentary canal and it has been proposed that the plague bacterium evolved from the latter. Analysis of the genome sequence suggested that it had acquired many genes from other bacteria and viruses. During the evolutionary transition towards becoming the plague bacterium, genes required for life in the intestinal tract decayed, says Nature.

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