After simmering in Asia for more than 1,000 years, cholera has swept across the world in pandemics seven times since 1817. The disease produces diarrhea so severe that it can be fatal. In a step toward developing a vaccine or new drugs for cholera, investigators have now read the complete DNA sequence of Vibrio cholera, the bacterium responsible for the illness.
A group led by Claire M. Fraser of the Institute for Genomic Research in Rockville, Md., reports in the Aug. 3 Nature that the microbe has an estimated 3,885 genes on its two circular chromosomes. The scientists found that most of the genes predicted to have essential cell functions or play a role in causing cholera reside on the larger chromosome. The smaller chromosome contains a high proportion of genes that have no identifiable function.
The scientists speculate that V. cholerae originally contained just the larger chromosome and at some point in its evolution picked up the additional DNA from another microorganism.
Such gene transfers can play a major role in altering the character of a bacterium (SN: 7/22/00, p. 60: Pass the Genes, Please). The genome of V. cholerae “provides a starting point for understanding how a free-living environmental organism emerged to become a significant pathogen,” Fraser and her colleagues say.