Analysis of virulence plasmid gene expression defines three classes of effectors in the type III secretion system of Shigella flexneri.
Proteins directly involved in entry and dissemination of Shigella flexneri into epithelial cells are encoded by a virulence plasmid of 200 kb. A 30-kb region (designated the entry region) of this plasmid encodes components of a type III secretion (TTS) apparatus, substrates of this apparatus and their dedicated chaperones. During growth of bacteria in broth, expression of these genes is induced at 37 degrees C and the TTS apparatus is assembled in the bacterial envelope but is not active. Secretion is activated upon contact of bacteria with host cells and is deregulated in an ipaB mutant. The plasmid encodes four transcriptional regulators, VirF, VirB, MxiE and Orf81. VirF controls transcription of virB, whose product is required for transcription of entry region genes. MxiE, with the chaperone IpgC acting as a co-activator, controls expression of several effectors that are induced under conditions of secretion. Genes under the control of Orf81 are not known. The aim of this study was to define further the repertoires of virulence plasmid genes that are under the control of (i) the growth temperature, (ii) each of the known virulence plasmid-encoded transcriptional regulators (VirF, VirB, MxiE and Orf81) and (iii) the activity of the TTS apparatus. Using a macroarray analysis, the expression profiles of 71 plasmid genes were compared in the wild-type strain grown at 37 and 30 degrees C and in virF, virB, mxiE, ipaB, ipaB mxiE and orf81 mutants grown at 37 degrees C. Many genes were found to be under the control of VirB and indirectly of VirF. No alteration of expression of any gene was detected in the orf81 mutant. Expression of 13 genes was increased in the secretion-deregulated ipaB mutant in an MxiE-dependent manner. On the basis of their expression profile, substrates of the TTS apparatus can be classified into three categories: (i) those that are controlled by VirB, (ii) those that are controlled by MxiE and (iii) those that are controlled by both VirB and MxiE. The differential regulation of expression of TTS effectors in response to the TTS apparatus activity suggests that different effectors might be required at different times following contact of bacteria with host cells.
Gall
Tony Le
TL
Laboratoire de Bactériologie, Faculté de Médecine de Brest, F-29285 Brest Cedex, France.|INSERM E0339, Faculté de Médecine Xavier Bichat, 16 rue Henri Huchard, F-75018 Paris, France.
Mavris
Maria
M
Unité de Pathogénie Microbienne Moléculaire, INSERM U389, Institut Pasteur, 25 rue du Dr Roux, F-75724 Paris Cedex 15, France.
Martino
Maria Celeste
MC
University Roma La Sapienza, Sez Sci Microbiol, Dipartimento Biol Cellulare & Sviluppo, Via Sardi 70, Rome, I-00185 Italy.
Bernardini
Maria Lina
ML
University Roma La Sapienza, Sez Sci Microbiol, Dipartimento Biol Cellulare & Sviluppo, Via Sardi 70, Rome, I-00185 Italy.
Denamur
Erick
E
INSERM E0339, Faculté de Médecine Xavier Bichat, 16 rue Henri Huchard, F-75018 Paris, France.
Parsot
Claude
C
Unité de Pathogénie Microbienne Moléculaire, INSERM U389, Institut Pasteur, 25 rue du Dr Roux, F-75724 Paris Cedex 15, France.
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D009154:Mutation; D020411:Oligonucleotide Array Sequence Analysis / Q000379:methods; D010957:Plasmids / Q000235:genetics*; D012763:Shigella flexneri / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity*; D013696:Temperature; D014158:Transcription, Genetic; D014774:Virulence
D001426:Bacterial Proteins