Mutation in the relA Gene of Vibrio cholerae Affects In Vitro and In Vivo Expression of Virulence Factors
IR@IICB: CSIR-Indian Institute of Chemical Biology, Kolkata
View Archive Info| Field | Value | |
| Title |
Mutation in the relA Gene of Vibrio cholerae Affects In Vitro
and In Vivo Expression of Virulence Factors
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| Creator |
Haralalka, Shruti
Nandi, Suvobroto Bhadra, Rupak K |
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| Subject |
Infectious Diseases and Immunology
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| Description |
The relA gene product determines the level of (p)ppGpp, the effector nucleotides of the bacterial stringent
response that are also involved in the regulation of other functions, like antibiotic production and quorum
sensing. In order to explore the possible involvement of relA in the regulation of virulence of Vibrio cholerae, a
relA homolog from the organism (relAVCH) was cloned and sequenced. The relAVCH gene encodes a 738-aminoacid
protein having functions similar to those of other gram-negative bacteria, including Escherichia coli. A
�relA::kan allele was generated by replacing �31% of the open reading frame of wild-type relA of V. cholerae El
Tor strain C6709 with a kanamycin resistance gene. The V. cholerae relA mutant strain thus generated, SHK17,
failed to accumulate (p)ppGpp upon amino acid deprivation. Interestingly, compared to the wild type, C6709,
the mutant strain SHK17 exhibited significantly reduced in vitro production of two principal virulence factors,
cholera toxin (CT) and toxin-coregulated pilus (TCP), under virulence gene-inducing conditions. In vivo
experiments carried out in rabbit ileal loop and suckling mouse models also confirmed our in vitro results. The
data suggest that (p)ppGpp is essential for maximal expression of CT and TCP during in vitro growth, as well
as during intestinal infection by virulent V. cholerae. Northern blot and reverse transcriptase PCR analyses
indicated significant reduction in the transcript levels of both virulence factors in the relA mutant strain
SHK17. Such marked alteration of virulence phenotypes in SHK17 appears most likely to be due to down
regulation of transcript levels of toxR and toxT, the two most important virulence regulatory genes of V. cholerae.
In SHK17, the altered expression of the two outer membrane porin proteins, OmpU and OmpT, indicated that
the relA mutation most likely affects the ToxR-dependent virulence regulatory pathway, because it had been
shown earlier that ToxR directly regulates their expression independently of ToxT.
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| Date |
2003
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| Type |
Article
PeerReviewed |
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| Format |
application/pdf
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| Identifier |
http://www.eprints.iicb.res.in/556/1/JOURNAL_OF_BACTERIOLOGY%2C185(_16)%2C_4672%2D4682[41].pdf
Haralalka, Shruti and Nandi, Suvobroto and Bhadra, Rupak K (2003) Mutation in the relA Gene of Vibrio cholerae Affects In Vitro and In Vivo Expression of Virulence Factors. JOURNAL OF BACTERIOLOGY, 185 (16). pp. 4672-4682. |
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| Relation |
http://dx.doi.org/10.1128/JB.185.16.4672–4682.2003
http://www.eprints.iicb.res.in/556/ |
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