Biology subjects

MEYER, D. F.

Publications and source records attributed to MEYER, D. F..

7 recordsLinked to original sources

bioRxiv2026

Galleria mellonella as a novel invertebrate model for studying Ehrlichia ruminantium pathogenesis and host-pathogen interactions

Ehrlichia ruminantium, the causative agent of heartwater disease, is an obligate intracellular bacterium that poses significant economic threats to livestock production in endemic regions. Current research models present substantial ethical, logistical, and economic constraints, particularly for studying host-pathogen interactions within arthropod vectors. Here we establish Galleria mellonella larvae as a tractable invertebrate infection model for Ehrlichia ruminantium, enabling experimental investigation of pathogen persistence and host-pathogen interactions in an arthropod system. Following infection, G. mellonella proved susceptible to E. ruminantium with moderate mortality and remarkable bacterial persistence. Using rhodamine-labeled bacteria and fluorescence microscopy, we tracked bacterial dissemination from injection sites to systemic distribution in characteristic segmental patterns throughout the larval body. Critically, we confirmed intracellular localization of E. ruminantium within hemocytes, the primary immune cells of G. mellonella. Quantitative PCR analysis revealed stable bacterial loads over the study period, indicating bacterial persistence within the host. These findings demonstrate that E. ruminantium can hijack the innate immune system of G. mellonella, similar to its behavior in natural hosts. The segmental bacterial distribution suggests exploitation of hemolymph circulation and sessile hemocyte populations, providing new insights into potential mechanisms of pathogen persistence. This model offers significant advantages: ethical acceptability, cost-effectiveness, experimental tractability, and compatibility with high-throughput screening approaches. The G. mellonella system represents a valuable complement to existing mammalian models and provides a unique platform for investigating arthropod-specific aspects of E. ruminantium biology, screening antimicrobial compounds, and understanding mechanisms of immune evasion that may inform strategies for heartwater disease control.

microbiology↗

bioRxiv2025

Prevalence of Heartwater in Guadeloupe (2024): Stable endemicity and Evidence of Spread to Les Saintes

Heartwater is a tick-borne disease caused by Ehrlichia ruminantium and remains endemic in the Guadeloupe archipelago. While previous data from 1989 suggested a seroprevalence of 22% in cattle, no updated figures were available for livestock, and certain islands such as Les Saintes were considered disease-free. This study aimed to update the sero-epidemiological status of heartwater in cattle and goats across Guadeloupe in 2024. Blood samples were collected from 261 cattle and 135 goats from all islands. Serological testing using the MAP1B ELISA was performed, and true seroprevalence was estimated using a simplified stochastic model that accounts for test sensitivity, specificity, and sample uncertainty. The mean cattle seroprevalence was estimated at 28% (95% CI [22-34%]), with no significant differences between Basse-Terre, Grande-Terre, and Marie-Galante. Importantly, seropositive goats were identified on all major islands, including Les Saintes. Our findings suggest that heartwater remains endemically stable in Guadeloupe since the 1980s and reveal for the first time its serological presence in Les Saintes. These results emphasize the importance of strengthening regional surveillance systems, including veterinary reporting, serological monitoring, and coordinated efforts to prevent further spread across the Caribbean.

immunology↗

bioRxiv2025

Dissection and internal observation of the giant tropical bont tick Amblyomma variegatum

Ticks are parasites arthropods that feed on the blood of animals and humans, serving as vectors responsible for numerous diseases worldwide. The tropical bont tick, Amblyomma variegatum, is the primary vector of Ehrlichia ruminantium, the causative agent of heartwater, endemic in sub-Saharan and southern Africa and several Caribbean islands. Due to their economic and public health impacts, A. variegatum and heartwater have been classified as high-consequence foreign animal diseases and pests by the United States Department of Agricultures Animal and Plant Health Inspection Service. Understanding the ecology and biology of A. variegatum is thus crucial to describe the tick-bacteria interactions and thus developing effective control methods. A key initial step in this endeavor involves the precise isolation and detailed functional characterization of tick organs to better understand vector competence. However, complete anatomical descriptions of internal structures within the Amblyomma genus remain scarce. In this study, we present a thorough characterization of the internal anatomy of A. variegatum. By accurately identifying and mapping organs of interest, we highlight notable morphological differences from other tick species. This work not only enhances our understanding of A. variegatum anatomy but also serves as a crucial resource for investigating tick-borne disease transmission. Ultimately, these findings support the development of targeted vector control strategies, applicable to both endemic and non-endemic regions.

zoology↗

bioRxiv2025

PPIFold: A Tool for Analysis of Protein-Protein Interaction from AlphaPullDown

Protein structure and protein-protein interaction (PPI) predictions based on coevolution have transformed structural biology, but managing pre-processing and post-processing can be complex and time-consuming, making these tools less accessible. Here, we introduce PPIFold, a pipeline built on the AlphaPulldown Python package, designed to automate file handling and streamline the generation of outputs, facilitating the interpretation of PPI prediction results. The pipeline was validated on the bacterial Type 4 Secretion System nanomachine, demonstrating its effectiveness in simplifying PPI analysis and enhancing accessibility for researchers.

bioinformatics↗

bioRxiv2021

Ehrlichia ruminantium uses its transmembrane protein Ape to adhere to host bovine aortic endothelial cells

AO_SCPLOWBSTRACTC_SCPLOWEhrlichia ruminantium is an obligate intracellular bacterium, transmitted by ticks of the genus Amblyomma and responsible for heartwater, a disease of domestic and wild ruminants. High genetic diversity of E. ruminantium strains hampers the development of an effective vaccine against all strains present in the field. In order to develop strategies for the control of heartwater through both vaccine and alternative therapeutic approaches, it is important to first gain a better understanding of the early interaction of E. ruminantium and its host cell. Particularly, the mechanisms associated with bacterial adhesion remain to be elucidated. Herein, we studied the role of E. ruminantium membrane protein ERGA_CDS_01230 (UniProt Q5FFA9), a probable iron transporter, in the adhesion process to host bovine aortic endothelial cells (BAEC). The recombinant version of the protein ERGA_CDS_01230, successfully produced in the Leishmania tarentolae system, is O-glycosylated. Following in vitro culture of E. ruminantium in BAEC, the expression of CDS ERGA_CDS_01230 peaks at the extracellular infectious elementary body stages. This result suggest the likely involvement of ERGA_CDS_01230, named hereafter Ape for Adhesion protein of Ehrlichia, in the early interaction of E. ruminantium with its host cells. We showed using flow cytometry and scanning electron microscopy that beads coated with recombinant ERGA_CDS_01230 (rApe) adheres to BAEC. In addition, we also observed that rApe interacts with proteins of the cell lysate, membrane and organelle fractions. Additionally, enzymatic treatment degrading dermatan and chondroitin sulfates on the surface of BAEC is associated with a 50% reduction in the number of bacteria in the host cell after a developmental cycle, indicating that glycosaminoglycans seem to play a role in the adhesion of E. ruminantium to the host cell. Finally, Ape induces a humoral response in vaccinated animals. Globally, our work identifying the role of Ape in E. ruminantium adhesion to host cells makes it a gold vaccine candidate and represents a first step toward the understanding of the mechanisms of cell invasion by E. ruminantium.

microbiology↗

bioRxiv2020

Possible biased virulence attenuation in the Senegal strain of Ehrlichia ruminantium by ntrX gene conversion from an inverted segmental duplication

Ehrlichia ruminantium is a tick-borne intracellular pathogen of ruminants that causes heartwater, a disease present in Sub-saharan Africa, islands in the Indian Ocean and the Caribbean, inducing significant economic losses. At present, three avirulent strains of E. ruminantium (Gardel, Welgevonden and Senegal isolates) have been produced by a process of serial passaging in mammalian cells in vitro, but unfortunately their use as vaccines do not offer a large range of protection against other strains, possibly due to the genetic diversity present within the species (Cangi et al. 2016). So far no genetic basis for virulence attenuation has been identified in any E. ruminantium strain that could offer targets to facilitate vaccine production. Virulence attenuated Senegal strains have been produced twice independently, and require many fewer passages to attenuate than the other strains. We compared the genomes of a virulent and attenuated Senegal strain and identified a likely attenuator gene, ntrX, a global transcription regulator and member of a two-component system that is linked to environmental sensing. This gene has an inverted partial duplicate close to the parental gene that shows evidence of gene conversion in different E. ruminantium strains. The pseudogenisation of the gene in the avirulent Senegal strain occurred by gene conversion from the duplicate to the parent, transferring a 4bp deletion which is unique to the Senegal strain partial duplicate amongst the wild isolates. We confirmed that the ntrX gene is not expressed in the avirulent Senegal strain by RT-PCR. The inverted duplicate structure combined with the 4bp deletion in the Senegal strain can explain both the attenuation and the faster speed of attenuation in the Senegal strain relative to other strains of E. ruminantium. Our results identify nrtX as a promising target for the generation of attenuated strains of E. ruminantium by random or directed mutagenesis that could be used for vaccine production.

genomics↗

bioRxiv2020

The super repertoire of type IV effectors in the pangenome of Ehrlichia spp. provides insights into host-specificity and pathogenesis

The identification of bacterial effectors is essential to understand how obligatory intracellular bacteria such as Ehrlichia spp. manipulate the host cell for survival and replication. Infection of mammals - including humans - by the intracellular pathogenic bacteria Ehrlichia spp. depends largely on the injection of virulence proteins that hijack host cell processes. Several hypothetical virulence proteins have been identified in Ehrlichia spp., but one so far has been experimentally shown to translocate into host cells via the type IV secretion system. However, the current challenge is to identify most of the type IV effectors (T4Es) to fully understand their role in Ehrlichia spp. virulence and host adaptation. Here, we predict the T4E repertoires of four sequenced Ehrlichia spp. and four other Anaplasmataceae as comparative models (pathogenic Anaplasma spp. and Wolbachia endosymbiont) using previously developed S4TE 2.0 software. This analysis identified 579 predicted T4Es (228 pT4Es for Ehrlichia spp. only). The effector repertoires of Ehrlichia spp. overlapped, thereby defining a conserved core effectome of 92 effectors shared by all strains. In addition, 69 species-specific T4Es were predicted with non-canonical GC% mostly in gene sparse regions of the genomes and we observed a bias in pT4Es according to host-specificity. We also identified new protein domain combinations, suggesting novel effector functions. This work presenting the predicted effector collection of Ehrlichia spp. can serve as a guide for future functional characterisation of effectors and design of alternative control strategies against these bacteria.

genomics↗