Biology subjects

Gal-Mor, O.

Publications and source records attributed to Gal-Mor, O..

5 recordsLinked to original sources

bioRxiv2026

Genome degradation in the c-di-GMP signaling pathways and serovar-specific YhjH-YciG interactions rewired motility regulation in Salmonella Paratyphi A

Salmonella enterica serovars Typhimurium (STM) and Paratyphi A (SPA) cause clinically distinct diseases, yet the molecular bases for their different lifestyles remain incompletely understood. Genome degradation, a hallmark of typhoidal Salmonella, results in extensive pseudogenization across multiple functional pathways. Here, we investigate how such gene inactivation rewires cyclic-di-GMP (c-di-GMP) signaling and flagellar motility regulation in SPA vs. STM. We show that YhjH, a conserved phosphodiesterase (PDE), is required for motility in STM but not in SPA, despite retaining PDE activity in both serovars. We demonstrate that this functional divergence is caused by pseudogenization of ycgR in SPA, which truncates the flagellar brake protein YcgR to a nonfunctional peptide, severing the link between c-di-GMP levels and flagellar motor control. Site directed mutagenesis in the YhjH active site and ectopic expression of intact YcgR from STM that restored YhjH-dependent motility regulation in SPA, confirmed this molecular mechanism. Additionally, using a bacterial two-hybrid (BACTH) genetic screen, we identified a serovar-specific interaction between YhjH and the general stress protein YciG in SPA, but not in STM. Computational RNA folding analysis predicted substantial differences in mRNA secondary structure and stability between the SPA and STM yhjH alleles, suggesting a potential role for synonymous mutations in this serovar-specific interaction. Together, these findings reveal how genome degradation can rewire regulatory networks, uncovering a fundamental difference in motility control between typhoidal and non-typhoidal Salmonella and suggest that these differences allow SPA motility under conditions that suppress motility in STM. IMPORTANCESalmonella enterica serovars Typhimurium (STM) and Paratyphi A (SPA) cause fundamentally different diseases in humans, yet the molecular basis for their distinct lifestyles and pathogenicity remains poorly understood. Genome degradation is a hallmark of typhoidal Salmonella, but its functional consequences for regulatory networks are largely unexplored. Here, we demonstrate that pseudogenization of ycgR in SPA dismantles c-di-GMP-mediated flagellar motor control, liberating SPA from an inhibitory brake that suppresses motility in STM. Additionally, we uncover a serovar-specific interaction between the phosphodiesterase YhjH and the general stress protein YciG in SPA, demonstrating that genome degradation can drive regulatory network rewiring beyond simple gene loss. These differences in motility regulation may facilitate the systemic pathogenesis and unique lifestyle of SPA.

microbiology↗

bioRxiv2026

Novel pESI-encoded autotransporter adhesin PeaP of epidemic Salmonella strains mediates adhesion, atypical biofilm formation, and poultry colonization

Salmonella enterica serovar Infantis (SIN) has rapidly become the dominant serovar in poultry worldwide, a success largely linked to the acquisition of the 285 kb megaplasmid pESI. While pESI-encoded antibiotic-resistance and iron-uptake systems are well characterized, pESI-mediated adhesion mechanisms remain poorly understood. Here we identify a novel pESI-encoded monomeric autotransporter adhesin, designated PeaP (pESI-encoded autotransporter protein), and demonstrate its pivotal role in atypical biofilm formation, interference with motility, and colonization of the chicken host. Biofilm assays revealed that pESI-harboring strain SIN 119944 forms robust biofilms at 37 {degrees}C and 42 {degrees}C, temperatures at which CsgD-dependent biofilm formation is negligible. Deletion of csgD did not impair this phenotype, whereas deletion of peaP abolished high-temperature biofilm development and restored motility to wild-type levels. Proteomic profiling of sessile versus planktonic cells highlighted PeaP as the most abundant pESI-derived protein in the biofilm fraction. AlphaFold-based modelling and negative-stain transmission electron microscopy showed that PeaP comprises a C-terminal {beta}-barrel and a 1,500 aa passenger domain with three tandem repeats, projecting filamentous appendages [~]37-nm from the outer membrane. Antibody blockade of PeaP reduced surface adhesion >6-fold, confirming its adhesive function. In an infection model of 2 day-old chicken, the peaP mutant displayed significantly lower colonization, indicating PeaP-mediated adhesion in vivo. Collectively, pESI-positive SIN deploys PeaP for CsgD-independent, temperature-tolerant biofilm formation and enhanced gastrointestinal colonization, providing a mechanistic basis for the epidemic spread of this multidrug-resistant pathogen in poultry.

microbiology↗

bioRxiv2025

HilE mediates motility thermoregulation in typhoidal Salmonella serovars at elevated physiological temperatures

Salmonella enterica is a diverse bacterial pathogen consisting of both typhoidal and nontyphoidal clinically distinct serovars. While typhoidal serovars cause in humans a systemic life-threatening enteric fever, nontyphoidal Salmonella (NTS) usually provoke a localized self-limiting gastroenteritis. Factors responsible for the different diseases caused by distinct Salmonella serovars are still poorly understood. Here, we show that at elevated physiological temperature, manifested during enteric fever (39-40{degrees}C), the transcription of the flagellar regulon, its protein translation, and flagella-mediated motility are all repressed in the typhoidal serovar, S. Paratyphi A (SPA). In contrast, the NTS representative serovar, S. Typhimurium, maintains similar or even higher levels of flagellar genes transcription, translation, and motility at 40{degrees}C relative to 37{degrees}C. By using a temperature-responsive flagellar reporter system in conjunction with a dense transposon mutagenesis screen we found that under elevated temperature, HilE negatively regulates SPA motility in a HilD-dependent manner. Since HilD is required for the transcriptional activation of FlhDC, the master regulator of the Salmonella flagellar-chemotaxis regulon, null deletion of hilE leads to motility upregulation at elevated temperature and the loss of motility thermoregulation in SPA. Interestingly, the absence of HilE also leads to a hyper-uptake of SPA by THP- 1 human macrophages at 40{degrees}C, but not at 37{degrees}C. Moreover, we show that a HilE-mediated motility thermoregulation is common to other typhoidal serovars, including S. Typhi and S. Sendai, but not to S. Paratyphi B, nor to various NTS serovars. Based on these results, we propose that HilE plays a unique role in motility thermoregulation in typhoidal Salmonella in a way that may restrain systemic dissemination of the pathogen via professional phagocytes, during the acute phase of enteric fever. AUTHOR SUMMARYDespite high genetic similarity, typhoidal and nontyphoidal Salmonella (NTS) strains of the single species Salmonella enterica cause in humans different diseases manifested as life-threatening enteric fever and short-term gastroenteritis, respectively. Currently, we are still ignorant about bacterial factors shaping the different lifestyles of typhoidal vs. NTS strains. Here we characterized differences in the regulation of Salmonella motility, which is an important virulence-associated phenotype, in response to changes in temperature, between typhoidal and NTS. We found that at elevated temperature, equivalent to the body temperature during enteric fever (39-40{degrees}C), the motility of typhoidal Salmonella, but not that of NTS is strongly repressed, by the negative regulator HilE in a HilD-dependent manner. Moreover, we demonstrate that HilE plays a previously unknown role in the interaction of S. Paratyphi A with phagocytic cells, as the absence of HilE caused enhanced uptake of this pathogen by human macrophages at elevated physiological temperature, but not at 37{degrees}C. Since motility thermoregulation by HilE was found in three different typhoidal serovars, but not in NTS, we hypothesize that motility regulation affects the interactions of Salmonella with its host and differences in its regulation contribute to the distinct pathogenicity of typhoidal vs. NTS strains.

microbiology↗

bioRxiv2022

Persistent Salmonella infections in humans are associated with mutations in the BarA/SirA regulatory pathway

The bacterial pathogen Salmonella enterica is able to establish persistent infections, evading antibiotics and the host immune system and providing a reservoir for recrudescence and transmission to new hosts. Non-typhoidal serovars (NTS) of S. enterica can establish and maintain symptomatic and asymptomatic long term human infections that may predispose carriers to inflammatory bowel diseases and cancer. Defining the adaptations and host-pathogen interactions enabling these persistent infections is key to devising more effective strategies to combat and prevent persistent bacterial infections. Using comparative genomics of 639 Salmonella NTS isolates belonging to 49 serovars that were longitudinally obtained from 256 salmonelosis patients during different stages of infection, we identified numerous genetic variations accruing over time in strains isolated from the same patient. Many of these changes were found in the same gene across multiple patients and serovars. Among these variant loci, genes encoding global transcriptional regulators were found to be the most commonly mutated between early and late same-patient isolates. Genetic changes in the SirA/BarA two-component regulatory system were particularly frequent, with mutations identified in 24 independent patients. Comparative RNA-Seq analysis revealed that distinct mutations in sirA/barA that arose independently in late isolates of multiple patients lead to significantly diminished expression of virulence-associated genes encoded in the Salmonella Pathogenicity Islands (SPIs) 1 and 4, many of which are known to be critical for host cell invasion and the production of enteritis. Using the salmonellosis mouse model we showed that these mutations in sirA/barA genes confer attenuated virulence in-vivo. Taken together, these data suggest that selection of mutations in the SirA/BarA pathway facilitates persistent Salmonella infection in humans, possibly by attenuating Salmonella virulence and its ability to cause inflammation.

genomics↗

bioRxiv2021

Intracellular Salmonella Paratyphi A is motile and differs in the expression of flagella-chemotaxis, SPI-1 and carbon utilization pathways in comparison to Intracellular S. Typhimurium

Although Salmonella Typhimurium (STM) and Salmonella Paratyphi A (SPA) belong to the same phylogenetic species, share large portion of their genome and express many common virulence factors, they differ vastly in their host specificity, the immune response they elicit, and the clinical manifestations they cause. In this work, we compared for the first time their intracellular trascriptomic architecture and cellular phenotypes during epithelial cell infection. While transcription induction of many metal transport systems, purines, biotin, PhoPQ and SPI-2 regulons was common in both intracellular SPA and STM, we identified 234 differentially expressed genes that showed distinct expression patterns in intracellular SPA vs. STM. Surprisingly, clear expression differences were found in SPI-1, motility and chemotaxis, and carbon (mainly citrate, galactonate and ethanolamine) utilization pathways, indicating that these pathways are regulated and possibly function differently, during their intracellular phase. Moreover, we show that the induction of flagella genes by intracellular SPA leads to cytosolic motility, a conserved trait specific to SPA. To the best of our knowledge, this is the first report of a flagellum-dependent intracellular motility of any Salmonella serovar in living host cells. Importantly, we demonstrate that the elevated expression of SPI-1 and motility genes by intracellular SPA results in increased invasiveness of SPA, following exit from host cells. We propose that such changes prime SPA towards new cycles of host cell infection and contribute to the ability of SPA to disseminate beyond the intestinal lamina propria of the human host, during enteric fever. IMPORTANCESalmonella enterica is a ubiquitous, facultative intracellular animal and human pathogen. Although non-typhoidal Salmonella (NTS) and typhoidal Salmonella serovars belong to the same phylogenetic species and share many virulence factors, the disease they cause in humans is very different. While the underlying mechanisms for these differences are not fully understood, one possible reason expected to contribute to their different pathogenicity is a distinct expression pattern of genes involved in host-pathogen interactions. Here, we compared the global gene expression and the intracellular behavior, during epithelial cell infection of S. Paratyphi A (SPA) and S. Typhimurium (STM), as prototypical serovars of typhoidal and NTS, respectively. Interestingly, we identified different expression patterns in key virulence and metabolic pathways, together with intracellular motility and increased invasiveness of SPA, following exit from infected cells. We hypothesize that these differences are pivotal to the invasive and systemic disease developed following SPA infection in humans.

microbiology↗