Constitutive expression of the phoP regulon attenuates Salmonella virulence and survival within macrophages.
The phoP genetic locus is a two-component regulatory system (phoP-phoQ) that controls the expression of genes essential for Salmonella typhimurium virulence and survival within macrophages. Strains with a phoP constitutive mutation (phenotype PhoPC) showed up to 10-fold greater expression of phoP-activated genes (pag loci) than did strains with a wild-type phoP locus (phenotype PhoP+). While the phoP constitutive mutation resulted in increased expression of pag loci, it also dramatically reduced the expression of other protein species. Comparison of the protein content of PhoP+ and PhoPC strains by two-dimensional protein gel electrophoresis demonstrated that at least 40 separate protein species were changed in expression as a result of this mutation. The PhoPC S. typhimurium were found to be attenuated for virulence and survival within macrophages. This finding suggests that a balanced PhoP-PhoQ regulatory response, which allows expression of phoP-repressed as well as -activated genes, is required for full virulence of S. typhimurium. We have further shown that small numbers of PhoPC bacteria can be used as a live attenuated vaccine to protect against mouse typhoid. As few as 15 PhoPC bacteria protected mice against challenge with 10(5) 50% lethal doses of wild-type organisms, suggesting that important protective antigens are regulated by the PhoP-PhoQ virulence regulon.
Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts 02115.
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SI
Miller
J J
JJ
Mekalanos
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000302:isolation & purification; D002470:Cell Survival; D002478:Cells, Cultured; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D015870:Gene Expression; D005809:Genes, Regulator; D005838:Genotype; D008264:Macrophages / Q000166:cytology / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008970:Molecular Weight; D010641:Phenotype; D012480:Salmonella Infections / Q000382:microbiology; D012486:Salmonella typhimurium / Q000235:genetics* / Q000472:pathogenicity / Q000502:physiology; D014774:Virulence / Q000235:genetics
D001426:Bacterial Proteins