Population Genetics of Vibrio cholerae
Rosario Morales, Gabriela Delgado, and Alejandro Cravioto
from: Vibrio cholerae: Genomics and Molecular Biology (Edited by: Shah M. Faruque and G. Balakrish Nair). Caister Academic Press, U.K. (2008)
The influence of evolutionary forces on the genetic diversity of natural populations of living organisms is the subject matter of population genetics. In the case of Vibrio cholerae, data obtained from detailed molecular studies of large populations of these bacteria have allowed for a better understanding of the epidemiology of diseases due to their presence in humans. The species has a high genetic diversity and a complex image of its population structure. There is also evidence of linkage disequilibrium and frequent intragenic and assortative recombination events in their housekeeping genes. Horizontal transfer of genes in V. cholerae is higher than those reported for Escherichia coli and Salmonella enterica. In spite of the frequent horizontal gene transfer, clonal lineages of Vibrio cholerae might persist for decades. The best example of this is the presence and survival of epidemic and pandemic clones over long periods of time. To date, there are four major genetic lines of toxigenic V. cholerae O1 biotype El Tor: an Australian clone (ET 1); the U.S. Gulf Coast clone (ET 2); the seventh pandemic clone isolated in the South East Asia together with the O139 "Bengal" clone (ET 3); and the clone that caused cholera in Latin America in the 1990's (ET 4). There are also isolated clones that have appeared over time under special conditions, e.g., serogroup O37 that was shown to have limited epidemic potential in the 1960's. Given the close evolutionary relationship between V. cholerae O1 and other non-O1 virulent serotypes and the fact that virulence genes can be transferred horizontally, new pathogenic strains of V. cholerae could arise in the future through the modification of existing clones that have the capacity to spread rapidly, and thus cause outbreaks of disease read more ...