Florent Sebbane

Volume 206, no. 9, e00173-24, 2024, https://doi.org/10.1128/jb.00173-24. Results, “The concentration of copper increases during digestion of the blood meals in the flea’s gut”: During a retrospective verification of the ICP-MS quantification procedure, we identified an additional two-fold dilution step in the sample preparation that had not been accounted for in the calculation of copper concentrations. Consequently, the copper concentrations reported in the Results section were underestimated by a factor of two. “…18.0 ± 2.0 µM at 12 h, to 20.1 ± 5.4 µM at 24 h, and reached 34.8 ± 4.6 µM…” should read “…36.0 ± 4.0 µM at 12 h, to 40 ± 11 µM at 24 h, and reached 70 ± 9 µM...” “…7.3 ± 7.0 µM…” should read “…15 ± 14 µM...”

Vector-borne pathogens must adapt to sharply distinct host environments, yet the regulatory logic that coordinates transitions between opposing host-specific programs remains poorly defined. Here, we identify a minimal regulatory module in the flea-borne pathogen Yersinia pestis that integrates vector transmission with resistance to mammalian innate immunity. Screening of flea-induced genes uncovered the regulator HdfR, which acts primarily through activation of maoP , encoding a nucleoid-associated protein. This HdfR-MaoP module promotes biofilm-dependent foregut blockage in the flea while coordinating baseline envelope adaptations that limit complement recognition and inducible responses that confer resistance to antimicrobial peptides under mammalian host-like conditions. Functional interchangeability of HdfR and MaoP homologs reveals evolutionary conservation of this regulatory logic, and pharmacological perturbation of the module sensitizes Y. pestis to antimicrobial peptides. Together, these findings define a parsimonious and evolutionarily conserved regulatory hub that orchestrates bacterial success across abrupt environmental transitions and exposes a tractable point of intervention.

Yersinia pestis , the etiological agent of plague, persists in an enzootic cycle involving mammals and fleas, requiring constant outer membrane (OM) adaptation to disparate host environments. One such pathway involves the glycine zipper 2TM domain-containing protein SlyB, a central component of the OM stress response and PhoPQ virulence pathway. While the OM is critical for virulence, the role of the OM lipoprotein SlyB in Y. pestis ecology and pathogenesis remains unknown. We show by phylogenetic analyses that slyB paralogs expanded in environmental bacteria, whereas the canonical slyB gene was under negative selective pressure during Y. pestis speciation from Yersinia pseudotuberculosis . Using rodent and flea infection models recapitulating Y. pestis natural history, we demonstrate that SlyB is specifically required to resist the mammalian immune system at 37°C, including neutrophil-mediated antimicrobial activity during lymph node colonization, but is dispensable in septicemic plague in rodents. Strikingly, SlyB is not required for flea colonization and resistance to the antimicrobial-peptide-based immunity of arthropods at lower temperatures. SlyB-dependent OM stress tolerance reveals a mechanism by which Y. pestis establishes bubonic plague, in line with its critical lipopolysaccharide structural switch. Our findings identify SlyB as an evolutionarily fine-tuned component of the Y. pestis envelope that mediates immune escape upon infection of mammalian hosts through maintenance of structural integrity.

The flea-borne transmission of Yersinia pestis relies on biofilm formation and metabolic adaptation within the insect gut. The pentose phosphate pathway (PPP) is central to these processes, yet the contribution of its non-oxidative branch remains poorly defined. Here, we investigated the roles of transketolase (TktA) and transaldolase (TalB) in plague bacillus physiology, metabolism, and flea colonization. TktA was essential for growth, preventing assessment of its role in biofilm formation and in vivo colonization. In contrast, TalB was dispensable for growth but required for optimal biofilm formation. In fleas, the ΔtalB mutant colonized the proventriculus but displayed a lower bacterial load than the wild-type strain at later time points, indicating a defect in sustained colonization. Metabolomic analyses revealed that disruption of tktA severely impairs PPP-associated metabolism, whereas loss of talB is associated with disruption of nucleotide homeostasis, carbon redistribution toward glycolysis, and a redox imbalance. These findings demonstrate a functional partitioning of the non-oxidative PPP and identify it as a key metabolic control node linking metabolism to colonization dynamics in Y. pestis.

Yersinia pestis , the causative agent of plague, has evolved a dual lifestyle enabling survival in both mammalian hosts and hematophagous flea vectors. While mammalian virulence has been extensively studied, the flea stage represents a highly selective and metabolically constraining environment that plays a decisive role in transmission. Following ingestion during a blood meal, Y. pestis establishes within the flea digestive tract, where it must withstand nutrient limitation, oxidative stress, osmotic pressure, and antimicrobial factors while forming a proventricular biofilm essential for gut blockage and subsequent transmission. This review synthesizes current knowledge of the metabolic strategies deployed by Y. pestis during flea colonization, highlighting a coordinated shift toward amino acid and lipid‐derived carbon sources, strict dependence on the pentose phosphate pathway, and a central role for lipoate metabolism. We discuss how these metabolic adaptations are tightly integrated with regulatory networks involving c‐di‐GMP signaling, two‐component systems, and global regulators such as RovM and Hfq, ensuring that biofilm formation occurs only when energetic conditions permit. Finally, we address unresolved questions regarding metabolic flux dynamics, interactions with the flea microbiota, and lineage‐specific variation, emphasizing the need for future systems‐level analyses. Together, this review positions flea colonization as an active and evolutionarily refined phase that shapes the transmission success of Y. pestis .

Yersinopine, a nicotianamine-like metallophore, was recently identified through biochemical analyses, but its in vivo production and functional role remain uncharacterized. In Yersinia pseudotuberculosis and its recent descendant Yersinia pestis , the cnt operon ( cntPQRLMI ) putatively encodes the biosynthesis and transport of yersinopine. In Y. pestis , however, two frameshift mutations disrupt cntQ , which encodes the predicted permease for yersinopine-metal complexes. This pseudogenization raises critical questions about the functional relevance of yersinopine in these closely related species. Here, we show that cnt operon expression is repressed by the zinc uptake regulator Zur and that both Y. pestis and Y. pseudotuberculosis secrete yersinopine under zinc-limited conditions. Unexpectedly, the operon mediates iron uptake in Y. pseudotuberculosis but supports zinc acquisition in Y. pestis . Moreover, targeted disruption of cntQ in Y. pseudotuberculosis shifts metal specificity from iron to zinc, mimicking the Y. pestis phenotype. Collectively, our results suggest that a single pseudogenization event could rewire metal uptake specificity. Our findings illustrate how evolutionary genome reduction can reshape bacterial physiology.

Yersinia pestis , the causative agent of plague, is a zoonotic bacterium that split at least 6,000 years ago from Yersinia pseudotuberculosis through plasmid acquisition, gene loss, and point mutations. These genetic events enabled a shift from the fecal-oral route to vector-borne transmission and facilitated systemic spread. In the course of its evolutionary history, Y. pestis has caused an unaccountable number of human outbreaks, at both regional and pandemic scales, of which three global pandemics have been documented from historical sources. The bacterium currently persists in sylvatic (enzootic) natural foci across Africa, Asia, and the Americas. Its persistence depends on the co-occurrence of reservoir hosts (mainly mammals) and competent vectors, primarily mammal ectoparasites, and their occurrence is shaped by environmental conditions. However, ecological variation among foci and limited epidemiological data still hinder our understanding of plague dynamics. This review examines the genetic evolution of Y. pestis , traces the bacterium’s history, including its global spread, and presents the main actors of sylvatic plague involved in the bacterium’s maintenance, with a special emphasis on the knowledge of vectors and hosts in countries that have reported cases of plague over the past decade. The global dispersal of Y. pestis has led to its adaptation to several distinct environments, highlighting the need for a comprehensive surveillance strategy for a better understanding of the ecological drivers of Y. pestis persistence and transmission within each of the geographical regions it is maintained in the natural environment.

La peste, causée par la bactérie Yersinia pestis, demeure une maladie mortelle à l’échelle mondiale. Ce pathogène est transmis principalement par les puces, dans lesquelles il s’adapte à l’environnement hostile de leur tube digestif, s’y multiplie et forme alors un biofilm dense qui obstrue l’entrée de sang. Cette obstruction favorise la transmission de la bactérie par régurgitation lors d’un repas sanguin. Ce processus repose sur un programme moléculaire initié chez le rongeur et prolongé chez l’insecte. Dans cette synthèse, nous décrivons l’environnement dans lequel Y. pestis évolue pour infecter les puces, ainsi que les modes de transmission et les mécanismes moléculaires impliqués, tout en adoptant une approche critique pour mieux comprendre les interactions entre Y. pestis et son vecteur, et explorer de nouvelles stratégies de lutte contre la propagation de l’agent de la peste.

The serum complement system is a cornerstone element of the innate immune response. Bacterial resistance to this system is a multifaceted process involving various proteins and molecular mechanisms. Here, we report several genes required for the growth of Yersinia pestis in serum. Among them, we found that ypo0337 encodes an outer-membrane-associated lectin that recruits factor H, C4BP and hemopexin, conferring resistance to the serum complement system. YPO0337 displays high sequence similarity with the SubB subunit of the AB₅ toxin from Escherichia coli, as well as other SubB-like proteins, and subB from E. coli restores the ability of Y. pestis Δypo0337 mutant to resist to serum complement. Altogether, the data suggest that at least two members of the SubB protein family function as virulence factors, conferring resistance to serum complement through a unique mode of action.

Background/Objectives: Yersinia pestis is an important zoonotic pathogen responsible for the rare but deadly disease of people with bubonic, septic, or pneumonic forms of plague. The emergence of multidrug-resistant Y. pestis strains has attracted more and more researchers’ attention to the search for molecular targets for antivirulence therapy, including anti-nutritional-virulence therapy. The glnALG operon plays a crucial role in regulating the nitrogen content within a bacterial cell. This operon codes for three genes: the structural gene glnA and the two regulatory genes glnL and glnG. In this study, we tested the effect of the deletion of glnA and glnALG on the pathogenic properties of Y. pestis. Methods: To assess the contribution of nitrogen metabolism to Y. pestis virulence, knockout mutants ΔglnA and ΔglnALG were constructed. The former was unable to synthesize glutamine, while the latter was not only defective in glutamine synthesis but also lacked the two-component sensor–transcriptional activator pair GlnL and GlnG, which could partially compensate for the decrease in intracellular glutamine concentrations by transporting it from the host or by catabolic reactions. For vaccine studies, immunized mice and guinea pigs were injected s.c. with 200 LD₁₀₀ of the wild-type Y. pestis strain. Results: A single knockout mutation in the glnA gene did not affect the virulence of Y. pestis in mice and guinea pigs. Knockout of the entire glnALG gene cluster was required for attenuation in these animals. The ΔglnALG strain of Y. pestis did not cause death in mice (LD₅₀ > 10⁵ CFU) and guinea pigs (LD₅₀ > 10⁷ CFU) when administered subcutaneously and provided 100% protection of animals when subsequently infected with 200 LD₁₀₀ of the Y. pestis virulent wild-type strain 231. Conclusions: Y. pestis, defective in both the glutamine synthetase GlnA and the two-component sensor–transcriptional activator pair GlnL-GlnG, completely lost virulence and provided potent protective immunity to mice and guinea pigs subsequently challenged with a wild-type Y. pestis strain, demonstrating the potential use of the glnALG operon as a new molecular target for developing a safe and efficient live plague vaccine.