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VGJphi integration and excision mechanisms contribute to the genetic diversity of Vibrio cholerae epidemic strains.

ABSTRACT: Most strains of Vibrio cholerae are not pathogenic or cause only local outbreaks of gastroenteritis. Acquisition of the capacity to produce the cholera toxin results from a lysogenic conversion event due to a filamentous bacteriophage, CTX. Two V. cholerae tyrosine recombinases that normally serve to resolve chromosome dimers, XerC and XerD, promote CTX integration by directly recombining the ssDNA genome of the phage with the dimer resolution site of either or both V. cholerae chromosomes. This smart mechanism renders the process irreversible. Many other filamentous vibriophages seem to attach to chromosome dimer resolution sites and participate in the rapid and continuous evolution of toxigenic V. cholerae strains. We analyzed the molecular mechanism of integration of VGJ, a representative of the largest family of these phages. We found that XerC and XerD promote the integration of VGJ into a specific chromosome dimer resolution site, and that the dsDNA replicative form of the phage is recombined. We show that XerC and XerD can promote excision of the integrated prophage, and that this participates in the production of new extrachromosomal copies of the phage genome. We further show how hybrid molecules harboring the concatenated genomes of CTX and VGJ can be produced efficiently. Finally, we discuss how the integration and excision mechanisms of VGJ can explain the origin of recent epidemic V. cholerae strains.

SUBMITTER: Das B

PROVIDER: S-EPMC3038760 | biostudies-other | 2011 Feb

REPOSITORIES: biostudies-other

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VGJphi integration and excision mechanisms contribute to the genetic diversity of Vibrio cholerae epidemic strains.

Das Bhabatosh B Bischerour Julien J Barre François-Xavier FX

Proceedings of the National Academy of Sciences of the United States of America 20110124 6

Most strains of Vibrio cholerae are not pathogenic or cause only local outbreaks of gastroenteritis. Acquisition of the capacity to produce the cholera toxin results from a lysogenic conversion event due to a filamentous bacteriophage, CTX. Two V. cholerae tyrosine recombinases that normally serve to resolve chromosome dimers, XerC and XerD, promote CTX integration by directly recombining the ssDNA genome of the phage with the dimer resolution site of either or both V. cholerae chromosomes. This ...[more]

PMID: 21262799

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Project description:Cholera, an acute diarrheal disease, is caused by pathogenic strains of Vibrio cholerae generated by the lysogenization of the filamentous cholera toxin phage CTXΦ. Although CTXΦ phage in the classical biotype are usually integrated solitarily or with a truncated copy, those in El Tor biotypes are generally found in tandem and/or with related genetic elements. Due to this structural difference in the CTXΦ prophage array, the prophage in the classical biotype strains does not yield extrachromosomal CTXΦ DNA and does not produce virions, whereas the El Tor biotype strains can replicate the CTXΦ genome and secrete infectious CTXΦ phage particles. However, information on the CTXΦ prophage array structure of pathogenic V. cholerae is limited. Therefore, we investigated the complete genomic sequences of five clinical V. cholerae isolates obtained in Kolkata (India) during 2007 to 2011. The analysis revealed that recent isolates possessed an altered CTXΦ prophage array of the prototype El Tor strain. These strains were defective in replicating the CTXΦ genome. All recent isolates possessed identical rstA and intergenic sequence 1 (Ig-1) sequences and comparable rstA expression in the prototype El Tor strain, suggesting that the altered CTXΦ array was responsible for the defective replication of the prophage. Therefore, CTXΦ structures available in the database and literatures can be classified as replicative and nonreplicative. Furthermore, V. cholerae epidemic strains became capable of producing CTXΦ phage particles since the 1970s. However, V. cholerae epidemic strains again lost the capacity for CTXΦ production around the year 2010, suggesting that a significant change in the dissemination pattern of the current cholera pandemic occurred. IMPORTANCE Cholera is an acute diarrheal disease caused by pathogenic strains of V. cholerae generated by lysogenization of the filamentous cholera toxin phage CTXΦ. The analysis revealed that recent isolates possessed altered CTXΦ prophage array of prototype El Tor strain and were defective in replicating the CTXΦ genome. Classification of CTXΦ structures in isolated years suggested that V. cholerae epidemic strains became capable of producing CTXΦ phage particles since the 1970s. However, V. cholerae epidemic strains again lost the capacity for CTXΦ production around the year 2010, suggesting that a critical change had occurred in the dissemination pattern of the current cholera pandemic.

Project description:Human challenge studies are instrumental for testing cholera vaccines, but these studies use outdated strains and require inpatient facilities. Here, we created next-generation isogenic Ogawa and Inaba O1 V. cholerae challenge strains (ZChol strains) derived from a contemporary Zambian clinical isolate representative of current dominant pandemic V. cholerae. Since the primary mechanism of immune protection against cholera is thought to be antibody responses that limit V. cholerae colonization and not the diarrheagenic actions of cholera toxin, these strains were rendered nontoxigenic. In infant mice, the ZChol strains did not cause diarrhea and proved to accurately gauge reduction in intestinal colonization mediated by effective vaccination. ZChol strains were also valuable as targets for measuring vibriocidal antibody responses. Using barcoded ZChol strains, we discovered that vaccination and passive immunity in the infant mouse model tightens the infection bottleneck without restricting pathogen expansion during intestinal infection. Collectively, our findings suggest that ZChol strains have the potential to enhance the safety, relevance, and scope of future cholera vaccine challenge studies and be valuable reagents for studies of immunity to cholera. IMPORTANCE Human challenge studies are a valuable method for testing the efficacy of cholera vaccines. However, challenge studies cannot be performed in countries of cholera endemicity due to safety concerns; also, contemporary pandemic Vibrio cholerae strains are not used in current challenge studies. To facilitate cholera research, we derived nontoxigenic challenge strains of both V. cholerae serotypes from a 2016 clinical isolate from Zambia and demonstrated how they can be used to gauge cholera immunity accurately and safely. These strains were also genetically barcoded, adding the potential for analyses of V. cholerae population dynamics to challenge studies. Preclinical analyses presented here suggest that these strains have the potential to enhance the safety, relevance, and scope of future cholera vaccine challenge studies and be valuable reagents for studies of immunity to cholera.

Dataset Information

VGJphi integration and excision mechanisms contribute to the genetic diversity of Vibrio cholerae epidemic strains.

Publications

VGJphi integration and excision mechanisms contribute to the genetic diversity of Vibrio cholerae epidemic strains.

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