Satellite phage TLCφ enables toxigenic conversion by CTX phage through dif site alteration (original) (raw)

Nature volume 467, pages 982–985 (2010)Cite this article

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Abstract

Bacterial chromosomes often carry integrated genetic elements (for example plasmids, transposons, prophages and islands) whose precise function and contribution to the evolutionary fitness of the host bacterium are unknown. The CTXφ prophage, which encodes cholera toxin in Vibrio cholerae1, is known to be adjacent to a chromosomally integrated element of unknown function termed the toxin-linked cryptic (TLC)2. Here we report the characterization of a TLC-related element that corresponds to the genome of a satellite filamentous phage (TLC-Knφ1), which uses the morphogenesis genes of another filamentous phage (fs2φ) to form infectious TLC-Knφ1 phage particles. The TLC-Knφ1 phage genome carries a sequence similar to the dif recombination sequence, which functions in chromosome dimer resolution using XerC and XerD recombinases3. The dif sequence is also exploited by lysogenic filamentous phages (for example CTXφ) for chromosomal integration of their genomes. Bacterial cells defective in the dimer resolution often show an aberrant filamentous cell morphology3,4. We found that acquisition and chromosomal integration of the TLC-Knφ1 genome restored a perfect dif site and normal morphology to V. cholerae wild-type and mutant strains with dif filamentation phenotypes. Furthermore, lysogeny of a dif non-toxigenic V. cholerae with TLC-Knφ1 promoted its subsequent toxigenic conversion through integration of CTXφ into the restored dif site. These results reveal a remarkable level of cooperative interactions between multiple filamentous phages in the emergence of the bacterial pathogen that causes cholera.

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Primary accessions

GenBank/EMBL/DDBJ

Data deposits

The sequences described in the article are deposited in GenBank under accession numbers HM134797, HM134798, HM134799 and HM134800.

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Acknowledgements

We thank T. M. Zaved Waise and S. M. Nashir Udden for technical assistance. This research was funded in part by the National Institutes of Health (grants RO1-GM068851 and RO1-AI070963) under different sub-agreements between the Harvard Medical School and the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B). The ICDDR,B is supported by countries and agencies that share its concern for the health problems of developing countries.

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Authors and Affiliations

  1. Molecular Genetics Laboratory, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka-1212, Bangladesh ,
    Faizule Hassan, M. Kamruzzaman & Shah M. Faruque
  2. Department of Microbiology and Molecular Genetics, Harvard Medical School, 200 Longwood Avenue, Boston, Massachusetts 02115, USA,
    John J. Mekalanos

Authors

  1. Faizule Hassan
  2. M. Kamruzzaman
  3. John J. Mekalanos
  4. Shah M. Faruque

Contributions

F.H., M.K. and S.M.F. conducted the experiments and performed analyses of bacterial strains and phages. S.M.F. and J.J.M. designed the studies, analysed data and wrote the manuscript.

Corresponding author

Correspondence toShah M. Faruque.

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The authors declare no competing financial interests.

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This file contains Supplementary Methods, additional references, Supplementary Tables 1-6 and Supplementary Figures 1- 6 with legends. (PDF 2619 kb)

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Hassan, F., Kamruzzaman, M., Mekalanos, J. et al. Satellite phage TLCφ enables toxigenic conversion by CTX phage through dif site alteration.Nature 467, 982–985 (2010). https://doi.org/10.1038/nature09469

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Editorial Summary

The evolution of virulent Vibrio cholerae

It has been known since the 1990s that the cholera toxin genes in Vibrio cholerae are found in the integrated bacteriophage CTXΦ, located in the V. cholerae genome adjacent to toxin-linked cryptic (TLC), a chromosomal DNA element of unknown function. TLC is now shown to correspond to the genome of TLCΦ, a satellite filamentous phage that uses the morphogenesis genes of a third filamentous phage (fs2Φ) to form infectious particles. By reconstructing the events that lead to the acquisition of phage DNA and comparing these to the genome of pandemic strains, Hassan et al. obtain a model of how virulent V. cholerae strains evolve to become successful human pathogens.