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J. Bacteriol., May 1996, 2911-2915, Vol 178, No. 10
CK Schmitt, SC Darnell and AD O'Brien
The flgM gene of Salmonella typhimurium encodes a negative regulator of
flagellin synthesis that acts by inhibiting the flagellum-specific sigma
factor FliA (sigma 28), but only when a mutation in a flagellar basal body,
hook, or switch gene is present. We previously showed that FlgM is also
necessary for the virulence of S. typhimurium in the mouse model of typhoid
fever and proposed that FlgM is required to modulate the activity of the
FliA sigma factor, which, in turn, regulates a gene involved in virulence.
In this investigation, we observed that (i) the in vitro generation times
of flgM mutant and wild-type strains of S. typhimurium were
indistinguishable, as were the amounts of flagellin produced by the
strains; (ii) the 50% lethal doses of fliA mutant and wild-type strains of
S. typhimurium were similar in orally infected mice; and (iii) inactivation
of the FliA-regulated flagellin gene fliC in an flgM S. typhimurium mutant
resulted in a virulent phenotype. Therefore, we now conclude that
expression of the FliC flagellin subunit in an flgM strain is responsible
for the attenuated phenotype of an flgM mutant and that FliA does not
appear to positively regulate virulence genes in S. typhimurium. Our
results suggest that the normal regulation of flagellum synthesis appears
to be necessary for virulence and that there may be an advantage conferred
in vivo by expression of a particular flagellar phenotype of S.
typhimurium.
Copyright © 1996, American Society for Microbiology
The attenuated phenotype of a Salmonella typhimurium flgM mutant is related to expression of FliC flagellin
Department of Microbiology and Immunology, F. Edward Hebert School of Medicine, University of the Health Sciences, Bethesda, Maryland 20814- 4799, USA.
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