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Journal of Bacteriology, December 2003, p. 7231-7240, Vol. 185, No. 24
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.24.7231-7240.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Novel Type of Specialized Transduction for CTX or Its Satellite Phage RS1 Mediated by Filamentous Phage VGJ in Vibrio cholerae

Departamento de Genética, Centro Nacional de Investigaciones Científicas, AP 6412, Havana, Cuba

Received 25 July 2003/ Accepted 19 September 2003

The main virulence factor of Vibrio cholerae, the cholera toxin, is encoded by the ctxAB operon, which is contained in the genome of the lysogenic filamentous phage CTX. This phage transmits ctxAB genes between V. cholerae bacterial populations that express toxin-coregulated pilus (TCP), the CTX receptor. In investigating new forms of ctxAB transmission, we found that V. cholerae filamentous phage VGJ, which uses the mannose-sensitive hemagglutinin (MSHA) pilus as a receptor, transmits CTX or its satellite phage RS1 by an efficient and highly specific TCP-independent mechanism. This is a novel type of specialized transduction consisting in the site-specific cointegration of VGJ and CTX (or RS1) replicative forms to produce a single hybrid molecule, which generates a single-stranded DNA hybrid genome that is packaged into hybrid viral particles designated HybP (for the VGJ/CTX hybrid) and HybRS (for the VGJ/RS1 hybrid). The hybrid phages replicate by using the VGJ replicating functions and use the VGJ capsid, retaining the ability to infect via MSHA. The hybrid phages infect most tested strains more efficiently than CTX, even under in vitro optimal conditions for TCP expression. Infection and lysogenization with HybP revert the V. cholerae live attenuated vaccine strain 1333 to virulence. Our results reinforce that TCP is not indispensable for the acquisition of CTX. Thus, we discuss an alternative to the current accepted evolutionary model for the emergence of new toxigenic strains of V. cholerae and the importance of our findings for the development of an environmentally safer live attenuated cholera vaccine.

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