Biology subjects

Attaiech, L.

Publications and source records attributed to Attaiech, L..

6 recordsLinked to original sources

bioRxiv2026

The ArcZ small RNA activates SlyA production to control contact-dependent antibacterial killing and diffusible antifungal activity in Dickeya solani

Bacterial phytopathogens deploy diverse antimicrobial systems, including diffusible secondary metabolites and contact-dependent secretion apparatuses, to compete with coinhabiting microorganisms during host colonization. How the production of these distinct weapons is coordinated remains incompletely understood. Here, we identified a two-tier regulatory cascade by which the Hfq-dependent small RNA (sRNA) ArcZ controls both antibacterial and antifungal antagonism in the phytopathogen Dickeya solani. High-throughput RNA interactome analysis (RIL-seq) shows that ArcZ interacts broadly across the transcriptome and directly base-pairs with the 5' untranslated region of the mRNA encoding the MarR-family transcription factor SlyA, activating its translation. SlyA subsequently binds directly to selected promoter regions within the solanimycin biosynthetic cluster (sol) and the type VI secretion system (T6SS) loci and activates their transcription. The ArcZ-SlyA axis is required for solanimycin mediated antifungal activity against Kluyveromyces lactis and for T6SS-dependent killing of the sympatric pathogen Pectobacterium atrosepticum, demonstrating that the D. solani T6SS mediates interbacterial competition. A compensatory base-pairing mutation between ArcZ and slyA restores both competitive phenotypes, establishing this post-transcriptional interaction as a direct upstream determinant. Together, these results reveal an sRNA controlled regulatory axis that coordinates diffusible antifungal and contact-dependent antibacterial activities.

microbiology↗

bioRxiv2026

Heterogeneous dynamics of mobile genetic elements encode and spread antibiotic persistence in bacteria

Bacterial persisters are nonreplicating cells that transiently evade antibiotic killing within an otherwise susceptible, replicating population. While persister formation has traditionally been attributed to phenotypic heterogeneity, reversible functional variations among genetically identical cells, most studies lack direct genomic evidence to exclude the contribution of cryptic and reversible genetic variations. Here, we demonstrate that the dynamics of the Legionella pneumophila integrative and conjugative element (ICEs) pP36 encode and disseminate antibiotic persistence-like traits. During biofilm formation, pP36 undergoes heterogeneous chromosomal excision generating a subpopulation of nonreplicating persisters-like bacteria with a distinct molecular profile. pP36-mediated L. pneumophila growth rate heterogeneity significantly enhances bacterial survival under fluoroquinolone treatment. Our findings reveal that pP36 dynamics not only orchestrate physiological diversity but also serve as a vehicle for horizontal transfer of antibiotic persistence mechanisms among clinical Legionella isolates. While ICEs are recognized as key drivers of antibiotic resistance dissemination, this study establishes that ICEs-mediated phenotypic variations is a critical determinant of persister-like cell formation, reshaping our understanding of bacterial adaptability to antibiotic stress.

microbiology↗

bioRxiv2025

Host infection selects for sRNA variants that drive bacterial social cheating

Single-nucleotide mutations in regulatory small RNAs (sRNAs) represent a largely unexplored route to social cheating during bacterial infection. Here we show that arcZ, encoding a conserved Hfq-dependent sRNA in the plant pathogen Dickeya solani, undergoes recurrent single-nucleotide mutations during potato tuber infection. Five distinct arcZ alleles define a graded series of ArcZ functional impairment in which antifungal and protease activities are progressively reduced while virulence is compromised only in a subset of alleles. All five variants gain a fitness advantage exclusively during co-infection with wild-type arcZ1 cells. This advantage is strongest when variants are rare and declines as cheater frequency increases, ultimately correlating with reduced total bacterial productivity, the canonical signature of social cheating and a tragedy of the commons. No fitness benefit is detected in vitro. Transcriptomic profiling of five arcZ variants identifies a conserved core of 186 downregulated genes enriched in secreted and diffusible functions. Systematic genetic dissection, supported by quantitative proteomics, establishes BudAB-dependent acetoin production as the dominant cooperative public good exploited during infection. Wild-type arcZ1cells divert pyruvate flux toward acetoin via the BudAB pathway, maintaining a less acidic tissue environment that sustains disease progression; arcZ variants, which repress this pathway, exploit the resulting pH buffering without contributing to it. These results establish pleiotropic regulatory sRNAs as a previously unrecognized class of mutational targets for the emergence of social cheaters during host infection. StatementBacterial populations are not genetically uniform: variants that exploit the cooperative activities of their neighbors, social cheaters, can emerge rapidly within infected tissue and undermine collective bacterial productivity. We show that single-nucleotide mutations in the sRNA ArcZ of Dickeya solani are recurrently selected during potato infection, generating cheater variants that cease contributing to a shared metabolic benefit. Wild-type cells divert pyruvate toward acetoin, buffering tissue pH and sustaining disease; mutant variants exploit this pH maintenance without producing acetoin themselves. Because a single arcZ mutation simultaneously represses a conserved set of 186 genes, including genes involved in secreted and diffusible functions, regulatory sRNA genes represent a previously unrecognized and unusually efficient mutational target for the evolution of social cheating during infection.

microbiology↗

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↗