Publications

4693

Abstract Multicellular magnetotactic prokaryotes represent a unique group of obligately marine multicellular bacteria known for their ability to navigate along magnetic field lines thanks to ferrimagnetic nanocrystals. To date, two distinct spherical and ellipsoidal morphotypes have been described, typically ranging from 3 to 6 μm in diameter and comprising approximately 50 cells of the same species. Although widespread in highly reduced marine sediments, they are represented by solely three genera clustering into a monophyletic group within the Desulfobacterota. In this study, we report a third morphotype in reduced sediments of the Mediterranean Sea in Carry-le-Rouet, France, that is approximately 30 times more voluminous than any previously described form. Because their large size, we designated these multicellular bacteria as “giant” and explored their cell ultrastructure, ecological niche and physiology using magnetic enrichment and a combination of microscopy techniques and single-consortium genomics. Transmission electron microscopy and confocal microscopy images of several individual consortia revealed that they contain an average of 130 cells, each producing over 100 greigite magnetosomes arranged to optimize the overall magnetic moment. Phylogenomic analyses positioned giant multicellular magnetotactic prokaryotes, together with other morphotypes, in a previously undescribed genus and species within the Candidatus Magnetomoraceae family, named Magnetogigantoglobus mediterraneus. Although genetically divergent with a different ultrastructure, all multicellular magnetotactic prokaryotes seem to rely on sulfate reduction coupled to heterotrophy or autotrophy. We further discuss the significance of these findings in the context of the evolutionary history of multicellularity and magnetotaxis in prokaryotes.

Pear decline, caused by 'Candidatus Phytoplasma pyri', has emerged in Chilean pear orchards in recent years. While several Cacopsylla species are potential vectors of 'Ca. P. pyri', the disease's full epidemiological cycle remains uncertain. Cacopsylla bidens, present in Chilean orchards, has recently been reported as a vector. This study conducted year-long surveys in two commercial pear orchards across different Chilean regions, capturing C. bidens in zones with 'Ca. P. pyri'-infected pear trees. All developmental stages were collected, with peak abundances occurring in March and April. Outside the study zones, C. bidens were found in pine trees but not in adjacent cultivated areas. Two seasonal morphotypes, summer and winter forms, were identified. Molecular analysis detected 'Ca. P. pyri' in a high proportion of insects, with maximum infection rates in March and April. These findings advance our understanding of 'Ca. P. pyri' spatial and temporal dynamics and its potential role in 'Ca. P. pyri' spreading under Chilean field conditions.

Abstract BACKGROUND The Asian citrus psyllid, Diaphorina citri , vectors Candidatus Liberibacter asiaticus ( C Las) that causes citrus greening disease, which has devastated global citrus production. Current management primarily relies on the application of synthetic chemical insecticides, resulting in the evolution of resistance among D . citri populations. C Las is ingested by D . citri while feeding on infected plants and subsequently interacts with the gut epithelial surface to establish infection. To determine the functional significance of abundant gut surface proteins in D. citri during C Las uptake, we used RNA interference (RNAi) to silence nine key gut surface protein genes. RESULTS Following membrane feeding on double‐stranded RNAs (dsRNAs), transcript levels were reduced by 20–51% in adults and 28–50% in nymphs at 72 h, with higher knockdown efficiencies of 41–63% in adults and 30–81% in nymphs by 120 h. Some dsRNA treatments increased D. citri mortality by approximately 20% over the control treatment, and two treatments reduced honeydew production indicative of reduced feeding consistent with disrupted gut function. Silencing of several individual proteins, including alkaline phosphatase, cadherin, cluster of calcium‐transporting ATPase, croquemort and monocarboxylate transporter, reduced C Las uptake in nymphs and/or adults. CONCLUSION Silencing of abundant gut surface proteins in D. citri limited C Las uptake, establishing a functional basis for RNAi‐mediated suppression of pathogen uptake. While additional studies are needed to determine specific molecular interactions, these results identify gut surface proteins as promising targets for RNAi‐based interventions to reduce C Las uptake by psyllids. © 2026 Society of Chemical Industry.

ABSTRACT Vector-borne transmission of plant and animal pathogens requires active engagement of the vector’s immune system, as pathogens must overcome barriers and exploit host cellular mechanisms. Candidatus Liberibacter solanacearum (CLso) and C. L. asiaticus (CLas) are gram-negative, phloem-limited bacteria transmitted by the psyllids Bactericera trigonica and Diaphorina citri , respectively. Both pathogens induce endoplasmic reticulum (ER) stress and apoptosis in the midguts of their respective vectors, promoting their transmission. The protein kinase R-like endoplasmic reticulum kinase (PERK), a key regulator of ER stress and the unfolded protein response (UPR), plays a crucial role in modulating immunity. In this study, we investigated the role of PERK in CLso-induced apoptosis. PERK expression was downregulated in CLso-infected adult psyllids and midguts, yet immunostaining revealed a significant increase in phosphorylated (active) PERK in infected midguts, despite reduced gene expression. Additionally, ER stress-inducing treatments in both infected and uninfected psyllids demonstrated that CLso infection differentially regulates PERK expression. Interestingly, similar treatments in CLas-infected and uninfected D. citri yielded different results, suggesting species-specific immune responses. Furthermore, inhibition of PERK altered the expression of apoptosis-related genes in CLso-infected psyllids, indicating its involvement in CLso-induced apoptosis. Our findings suggest that PERK and UPR play a role in initiating immune responses at the ER interface in response to CLso, ultimately contributing to apoptosis, which may aid pathogen transmission. While the precise mechanisms by which CLso controls these processes remain unclear, this study provides new insights into how vector-borne plant and potentially animal pathogens manipulate host cellular pathways to enhance their spread. IMPORTANCE This study provides valuable insights into how vector-borne pathogens manipulate host cellular pathways to promote their survival and transmission. Candidatus Liberibacter solanacearum (CLso) and C. L. asiaticus (CLas) cause severe plant diseases, such as zebra chip in potatoes, carrot yellows, and huanglongbing (citrus greening), posing significant threats to global agriculture. By revealing the role of PERK and the unfolded protein response (UPR) in CLso-induced apoptosis, our findings contribute to the growing understanding of insect immunity and pathogen-host interactions. Understanding how CLso influences ER stress and immune signaling in its psyllid vector could lead to innovative strategies to disrupt pathogen persistence and transmission, ultimately supporting disease management efforts.

The X-disease phytoplasma (‘ Candidatus Phytoplasma pruni’) is an obligate pathogen that is capable of infection, persistence, and pathogenicity in both its major plant host ( Prunus spp.) and leafhopper vector ( Colladonus spp.) species. How ‘ Ca. P. pruni’ interacts with its plant and insect hosts, and how it alters its gene expression to do so, is unknown. Therefore, in this study, we conducted comparative RNA sequencing and differential gene expression analysis on ‘ Ca. P. pruni’-infected Prunus avium and Colladonus reductus samples. We found that the phytoplasma altered the expression of approximately 32% of its annotated protein-coding and pseudogenes, including intercellular transporters, proteolytic activity, and membrane structure, as well as upregulating genes associated with potential mobile units when in insect tissues versus in plant tissues. Most notably, differential expression was observed in genes that were identified by in silico analysis as being putative secreted effectors that may play a role in allowing phytoplasma infection and survival in these two very different host systems, as well as inducing X-disease in Prunus spp., which offers targets for control of this damaging pathogen by disrupting phytoplasma–host interactions. [Formula: see text] Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .