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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.
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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