Acquisition of classical CTX prophage from Vibrio cholerae O141 by El Tor strains aided by lytic phages and chitin-induced competence

S. M.Nashir Udden, M. Shamim Hasan Zahid, Kuntal Biswas, Qazi Shafi Ahmad, Alejandro Cravioto, G. Balakrish Nair, John J. Mekalanos, Shah M. Faruque

Research output: Contribution to journalArticlepeer-review

47 Scopus citations


The El Tor biotype of Vibrio cholerae O1, causing the current seventh pandemic of cholera, has replaced the classical biotype, which caused the sixth pandemic. The CTX prophages encoding cholera toxin in the two biotypes have distinct repressor (rstR) genes. Recently, new variants of El Tor strains that carry the classical type (CTXclass) prophage have emerged. These "hybrid" strains apparently originate through lateral gene transfer and recombination events. To explore possible donors of the CTXclass prophage and its mode of transfer, we tested environmental V. cholerae isolates for the presence of CTXclass prophage and mobility of the phage genome. Of the 272 environmental V. cholerae isolates tested, 6 were found to carry the CTXclass prophage; all of these belonged to the O141 serogroup. These O141 strains were unable to produce infectious CTX class phage or to transmit the prophage to recipient strains in the mouse model of infection; however, the CTXclass prophage was acquired by El Tor strains when cultured with the O141 strains in microcosms composed of filtered environmental water, a chitin substrate, and a V. cholerae O141-specific bacteriophage. The CTXclass prophage either coexisted with or replaced the resident CTXET prophage, resulting in El Tor strains with CTX genotypes similar to those of the naturally occurring hybrid strains. Our results support a model involving phages and natural chitin substrate in the emergence of new variants of pathogenic V. cholerae. Furthermore, the O141 strains apparently represent an alternative reservoir of the CTXclass phage genome, because the classical V. cholerae O1 strains are possibly extinct.

Original languageEnglish (US)
Pages (from-to)11951-11956
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number33
StatePublished - Aug 19 2008
Externally publishedYes


  • Hybrid Vibrio cholerae strain
  • Toxigenic Vibrio cholerae

ASJC Scopus subject areas

  • General


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