Institut de Biologie StructuraleGrenoble / France

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Deciphering regulatory network controlling the expression of Exolysin A

We have shown that the second messengers c-di-GMP and cAMP are involved in the regulation of ExlA. As observed for T3SS, the CyaB-cAMP / Vfr pathway positively controls the expression of exlBA, highlighting the similarities in the regulatory mechanism of the two main virulence factors of P. aeruginosa [1]. The screening of a library of 100,000 transposition mutants led to the identification of an inhibitor of the exlBA operon that we named ErfA (ExlA regulatory factor A). It belongs to the family of transcription factors of the XRE (Xenobiotic Response Element) type and has a C-terminal "Cupin" domain probably involved in signal detection. We confirmed that inactivation of erfA greatly increases the mutant cytotoxicity towards epithelial cells and in a Galleria infection model. The erfA gene is conserved in different Pseudomonas species, even those which do not have the exlBA operon. Genome-wide approaches (RNAseq and ChIPseq) have demonstrated that ErfA also controls an operon of two genes, ergAB (ErfA regulated genes A and B). This operon is in fact the only conserved target of ErfA in the different Pseudomonas species, while exlBA is only controlled by ErfA in P. aeruginosa. Analysis of the exlBA promoters of 446 Pseudomonas strains confirmed that the sequences vary according to the species and exhibit different regulatory binding sites, ensuring that this operon acquired by horizontal gene transfer (HGT) has an expression adapted to the survival conditions of the different species [2]. We recently extended the characterization to the 7 other ErfA type inhibitors encoded by the P. aeruginosa genome, by combining RNAseq and ChIPseq. This study showed that they are regulators controlling a small number of genes, generally contiguous to that of the regulator, the products of which are involved in metabolism [3].

Figure from Trouillon et al (2020) Nucleic Acids Res.

[1] Berry et al (2018) J Bacteriol. doi : 10.1128/JB.00135-18
[2] Trouillon et al (2020) Nucleic Acids Res. doi : 10.1093/nar/gkz1232
[3] Trouillon et al (2021) mSystems. doi : 10.1128/mSystems.00753-20