Biology subjects

Picq, K.

Publications and source records attributed to Picq, K..

3 recordsLinked to original sources

bioRxiv2024

Fis family members synergistically control the virulence of Legionella pneumophila

Legionella pneumophila virulence is controlled in a growth phase-dependent manner by a complex regulatory network involving several two-component systems, small regulatory RNAs and the translational CsrA regulator. Here, we address the additional role of Nucleoid-associated proteins (NAP) regulators in this network, by investigating the regulatory functions of the three Fis paralogs (Fis1, Fis2, Fis3), a unique feature among bacteria, in the infection cycle of L. pneumophila. Specifically, we show that deletion of fis1 has a major impact on L. pneumophila virulence, and that deletion of fis2 enhances the intensity of this phenotype. Consistently, RNA-seq analysis and reporter gene fusions demonstrate the predominant role of Fis1 in the regulation of many virulence-related genes, including those involved in the flagellum, pili biosynthesis, and Dot/Icm type 4 secretion machinery, as well as several genes encoding Dot/Icm effectors. Both Fis1 and Fis2 bind to AT-rich motifs upstream their target genes, but Fis1 with higher affinity than Fis2. Importantly, Fis1 and Fis2 would be capable of forming heterodimers that could bind with variable affinity to this AT-rich motif. It is also important to note that the three Fis proteins are not produced at the same time and in the same amounts. We therefore hypothesize that the duplication of fis genes in L. pneumophila is not simply a back-up system to compensate for potentially deleterious mutations in a fis gene, but rather a means to fine-tune the expression of targeted genes, particularly virulence genes. IMPORTANCEAppropriate control of virulence gene expression is crucial to the success of bacterial infection. Nucleoid-associated protein regulators, including Fis proteins, have been shown to participate in the virulence of several human pathogens. The importance of our discovery lies in the fact that L. pneumophila possesses three non-homologous Fis proteins instead of just one. We demonstrate that Fis1 and Fis2 are not functional duplicates of each other. On the contrary, Fis1 and Fis2 are synthesized neither simultaneously nor in equal amounts during the bacterial growth phase, and they cooperate to regulate virulence gene expression by targeting similar AT-rich motifs, albeit with distinct affinity, and by being capable of forming heterodimers. Taken together, our data suggest that the high conservation of fis gene duplication results from the need for fine-tuned control of Legionella virulence in response to its different environmental and human hosts, rather than from functional redundancy to circumvent deleterious fis mutations.

microbiology↗

bioRxiv2023

Dual control of host actin polymerization by a Legionella effector pair

Host actin cytoskeleton is often targeted by pathogenic bacteria through the secretion of effectors. Legionella pneumophila virulence relies on the injection of the largest known arsenal of bacterial proteins, over 300 Dot/Icm Type 4 Secretion System effectors, into the host cytosol. Here we define the functional interactions between VipA and LegK2, two effectors with antagonistic activities towards actin polymerization that have been proposed to interfere with the endosomal pathway. We confirmed the prominent role of LegK2 effector in Legionella infection, as the deletion of legK2 results in defects in the inhibition of actin polymerization at the Legionella Containing Vacuole, as well as in endosomal escape of bacteria and subsequent intracellular replication. More importantly, we observed the restoration of the{Delta} legK2 mutant defects, upon deletion of vipA gene, making LegK2/VipA the first example of effector-effector suppression pair that targets the actin cytoskeleton and whose functional interaction impacts L. pneumophila virulence. We demonstrated that LegK2 and VipA do not modulate each others activity in a metaeffector relationship. Instead, the antagonistic activities of the LegK2/VipA effector pair would target different substrates, Arp2/3 for LegK2 and G-actin for VipA, to temporally control actin polymerization at the LCV and interfere with phagosome maturation and endosome recycling, thus contributing to the intracellular life cycle of the bacterium. Strikingly, the functional interaction between LegK2 and VipA is consolidated by an evolutionary history that has refined the best effector repertoire for the benefit of L. pneumophila virulence.

microbiology↗

bioRxiv2019

Diverse conjugative elements silence natural transformation in Legionella species

Natural transformation, i.e. the uptake of DNA and its stable integration in the chromosome, is a major mechanism of horizontal gene transfer and is common in bacteria. The vast majority of bacterial genomes carry the specific genes involved in natural transformation, yet only a fraction of species are deemed naturally transformable. This is typically explained by the inability of standard laboratory conditions to induce this phenotypic trait. However, even when the inducing conditions are known, large intraspecific variations have been reported. In this study, we investigated the conservation and distribution of natural transformability in the human pathogen Legionella pneumophila. Using a panel of 113 clinical isolates, we found that natural transformability is relatively conserved but shows large variations inconsistent with the phylogeny. By conducting a genome-wide association study (GWAS) we identified the conjugative plasmid pLPL as a source of these intraspecific variations. We further show that the plasmid inhibits transformation by simultaneously silencing the genes required for DNA uptake and recombination, comEC, comEA, comF and comM. We identified a plasmid-encoded small RNA (sRNA), RocRp, as solely responsible for the silencing of natural transformation. RocRp is homologous to the highly conserved and chromosome-encoded RocR which controls the transient expression of the DNA uptake system. We show that RocRp can take over the function of RocR, by acting as a substitute, ensuring that the bacterial host of the conjugative plasmid does not become naturally transformable. Distinct homologs of this plasmid-encoded sRNA are found in diverse conjugative elements in other Legionella species, suggesting that silencing natural transformation is beneficial to these genetic elements. We propose that transformation-interfering factors are frequent genetic cargo of mobile genetic elements, accounting for intraspecific variations in natural transformation but also responsible for the apparent non-transformability of some species.

microbiology↗