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Deciphering the "master" gene of virulence and studies of gene expression during infection.

The regulatory protein FliZ of Xenorhabdus creates two sub-populations which express different infectious potential within an isogenic population of bacterial cells.

The approach consisting to construct by allelic exchange mutants unable to express a combination of factors is an appropriate strategy in the studies of host/pathogen interaction. In our scientific field, this approach was crucial because the (one by one) inactivation of effectors in P. luminescens and in X. nematophila rarely produced fully avirulent mutants. Consequently, our group and the Laboratory of Genetics of Bacterial Genomes (Antoine Danchin's group, Pasteur Institute) constructed eight knockout mutants in global regulators (2003 to 2007). The pathogenicity of these defective mutants examined after injection into the moth revealed that two of them are strongly altered in virulence. Therefore the flagellar regulator FliZ in Xenorhabdus, and the two-component regulatory system PhoPQ in Photorhabdus were particularly studied. Here, we only described works relative to FliZ.

  • In 2008, we showed that the transcriptional regulator FliZ of Xenorhabdusis responsible for the coupling of motility (flagellum) and virulence by controlling the expression of flagellum and hemolysin encoding genes (Lanois et al., 2008). In 2012, we characterized the FliZ regulon by RNASeq (Coll. Montpellier GenomiX - Génoscope Evry-CEA). The expression of 278 genes that encode proteins involved in the interaction with both invertebrates (such as hemolysin, proteases, lipases, antimicrobial molecules, protein involved in the interaction with the nematodes) is controlled by the transcriptional regulator FliZ.
  • The real-time study of gene expression during infection showed that FliZ-dependent genes are transcribed in late sepsis, when the insect is moribund (Coll. J.B. Ferdy, EDB, Toulouse). We also proposed that the stimulus present in the insect to turn “on” the regulon FliZ is the iron accessibility (Jubelin et al., 2011).

We also studied a heterogeneity phenomenon of the expression (at a given time, only a proportion of the bacterial cells expresses a gene) in the FliZ regulon. This phenotypic noise was described during in vitro growth (Jubelin et al., 2013) and observed during infection. We also showed that this heterogeneity is controlled by the concentration of the regulatory protein FliZ. That means that the population of X. nematophila is composed of a mixed culture of cells either expressing or not expressing FliZ-dependent genes. Accordingly, the possibility of cooperation between the bacterial subpopulations has been advanced and is currently worked.

See also

LANOIS A, JUBELIN G, GIVAUDAN A. 2008. FliZ, a flagellar regulator, is at the crossroads between motility, haemolysin expression and virulence in the insect pathogenic bacterium XenorhabdusMol Microbiol. 68:516-533.

JUBELIN G, PAGES S, LANOIS A, BOYER MH, GAUDRIAULT S, FERDY JB, GIVAUDAN A. 2011. Studies of the dynamic expression of the Xenorhabdus FliAZ regulon reveal atypical iron-dependent regulation of the flagellin and haemolysin genes during insect infection. Environ Microbiol. 13:1271-1284.

JUBELIN G, LANOIS A, SEVERAC D, RIALLE S, LONGIN C, GAUDRIAULT S, GIVAUDAN A. 2013. FliZ is a global regulatory protein rheostatically affecting the expression of flagellar and virulence genes in individual Xenorhabdus bacterial cells. PLoS genetics. 9(10): e1003915. doi:10.1371/journal.pgen.1003915