Biology subjects

Cloetens, P.

Publications and source records attributed to Cloetens, P..

9 recordsLinked to original sources

bioRxiv2026

Copper transport is required for metabolism and persistence of Toxoplasma gondii

Copper is a conserved cofactor, required for essential processes including aerobic respiration. Pathogens subvert host copper; however the mechanisms of copper uptake are not well understood. Here, we identify and validate two copper transporters of Toxoplasma gondii and determine the role of copper in parasite metabolism and pathogenesis. We show that Ctr1 is required for copper uptake. Deletion leads to undetectable parasite-associated copper, a significant growth defect and a metabolic shift from mitochondrial respiration with to glycolysis. Absence of Crt1 was fully and rapidly rescued by exogenous copper, which we believe is transported through the lower-affinity transporter Ctr2. Ctr2 is dispensable in rapid growth, however, has a role in parasite persistence in chronic infection, both in vitro and in vivo. Together, these findings reveal for the first time a critical role for copper uptake in shaping metabolic plasticity, and highlights the importance of nutrient availability in regulating apicomplexan metabolism.

cell biology↗

bioRxiv2025

Critical point drying of brain tissue for X-ray phase contrast imaging

X-ray phase contrast tomography is emerging as a powerful method for imaging large volumes of brain tissue at sub-cellular resolution. However, current sample preparation methods are largely inherited from visible light or electron microscopy workflows and hence are not optimised to exploit the full potential of X-ray contrast mechanisms. Here we propose to replace interstitial material by air to enhance X-ray phase contrast of the ultrastructural features. We used critical point drying (CPD) of heavy metal-stained mouse brain tissue to produce mechanically stable samples with preserved ultrastructure and enhanced refractive index boundaries, a nanofoam-like material that remains compatible with follow-up conventional resin embedding. Using two complementary synchrotron-based setups, a high-throughput microtomography beamline (P14, DESY) and a nanoscale holographic tomography beamline (ID16A, ESRF), we found that CPD samples consistently showed 2-4x stronger phase-shift signal than conventional resin-embedded tissue. The contrast gain remained consistent across samples, imaging conditions, and beamlines. Our results suggest that CPD offers a versatile route for preparing tissue for subcellular and ultrastructural-resolution X-ray imaging. It retains structural detail while improving signal, and is compatible with other processing procedures like femtosecond laser milling or electron microscopy, paving the path for biological tissue imaging beyond the mm3 scale.

neuroscience↗

bioRxiv2025

Cryo-Correlative Light and X-ray microscopies: Expanding the Intracellular Chemical Map

We introduce a powerful, integrated workflow that fuses cryo-optical fluorescence microscopy with cryogenic synchrotron radiation X-ray fluorescence nanoimaging to unlock unprecedented nanoscale insights into cellular ultrastructure and composition. Our method delivers sharp 2D and 3D visualizations enabling simultaneous elemental mapping, nanoparticle tracking, and imaging of mitochondrial features via a luminescent cyclometalated iridium complex. We further demonstrated that combining well-chosen molecular probes possessing different heavy elements (e.g. rhenium, iridium, bromine and iodine) allows elemental multiplex "painting" of different organelle to provide X-ray fluorescent elemental contrast of some intracellular structure. By eliminating the need for separate sample preparations, this streamlined approach maximizes limited synchrotron beamtime and dramatically accelerates data acquisition, setting a new benchmark for advanced cryo-nanoscale imaging studies.

cell biology↗

bioRxiv2025

Structure-Function Mapping of Olfactory Bulb Circuits with Synchrotron X-ray Nanotomography

Information is routed between brain areas via parallel streams. Neurons may share common inputs yet convey distinct information to different downstream targets. Here, we leverage the anatomical organisation of the mouse olfactory bulb (OB), where dozens of projection neurons (mitral and tufted cells, M/TCs) affiliate with a single input unit, a glomerulus1-3. To link functional properties of M/TCs to their anatomical glomerular association at scale, we combine in vivo two-photon (2P) imaging with synchrotron {micro}CT4-6 anatomical analysis and targeted X- ray nano-holotomography (XNH)7,8. Improving XNH resolution for mm3 volumes enables us to reliably identify subcellular features, automatically segment >80,000 cell nuclei in individual experiments, and delineate several hundred functionally imaged projection neurons and their detailed morphology, including up to 20 M/TCs per individual glomerulus ("sister" cells). In over 2400 sister cell pairs, we consistently find that odour response amplitudes to a panel of 47 monomolecular odours are conserved between sister cells, with, however, distinct responses to individual odours. Responses correlated with anatomical features such as cell body position and lateral dendritic arborisation. Thus, sister cells neither simply relay glomerular inputs nor are they dominated by network activity. Instead, they show a "balanced diversity" in their responses, enabling efficient encoding of odour stimuli whilst retaining the overall structure of odour space. Thus, synchrotron X-ray tomography can reliably link subcellular anatomy to function in a non-destructive way across the mm3 scale. With recent advances in X-ray optics9 and the emergence of 4th generation synchrotrons10,11, it becomes conceivable to extend this highly accessible approach to entire brain regions with increasing resolution.

neuroscience↗

bioRxiv2025

Self-supervised image restoration in coherent X-rayneuronal microscopy

Coherent X-ray microscopy is emerging as a transformative technology for neuronal imaging, with the potential to offer a scalable solution for reconstruction of neural circuits in millimeter sized tissue volumes. Specifically, X-ray holographic nanoto-mography (XNH) brings together outstanding capabilities in terms of contrast, spatial resolution and data acquisition speed. While recent XNH developments already enabled generating valuable datasets for neuro-sciences, a major challenge for reconstruction of neural circuits remained overcoming resolving power limits to distinguish smaller neurites and synapses in the reconstructed volumes. Here we present a self-supervised image restoration approach that simultaneously improves spatial resolution, contrast, and data acquisition speed. This enables revealing synapses with XNH, marking a major milestone in the quest for generating connectomes of full mammalian brains. We demonstrate that this method is effective for various types of neuronal tissues and acquisition schemes. We propose a scalable implementation compatible with multi-terabyte image volumes. Altogether, this work brings large-scale X-ray nanotomography to a new precision level.

neuroscience↗

bioRxiv2024

Uncovering nitroxoline activity spectrum, mode of action and resistance across Gram-negative bacteria

Nitroxoline is a bacteriostatic quinoline antibiotic, considered a metal chelator inhibiting the activity of RNA-polymerase1. Its clinical indications are limited to uncomplicated urinary tract infections (UTIs), with a clinical susceptibility breakpoint only available for Escherichia coli2. By testing > 1,000 clinical isolates, here we demonstrate a much broader activity spectrum and species-specific bactericidal activity, including multidrug-resistant Gram-negative bacteria for which therapeutic options are limited due to resistance. By combining systematic genetic and proteomic approaches with direct measurement of intracellular metals, we dissect nitroxoline perturbation of metal homeostasis and unveil additional effects on bacterial physiology. We show that nitroxoline affects outer membrane integrity, synergizing with large-scaffold antibiotics and resensitizing colistin-resistant Enterobacteriaceae in vitro and in vivo. We further characterise resistance mechanisms across E. coli, Acinetobacter baumannii and Klebsiella pneumoniae, recapitulating known E. coli resistance determinants and uncovering novel and conserved mechanisms across species, demonstrating their common effect on nitroxoline efflux.

microbiology↗

bioRxiv2019

Correlating STED and synchrotron XRF nano-imaging unveils the co-segregation of metals and cytoskeleton proteins in dendrites

Zinc and copper are involved in neuronal differentiation and synaptic plasticity but the molecular mechanisms behind these processes are still elusive due in part to the difficulty of imaging trace metals together with proteins at the synaptic level. We correlate stimulated emission depletion (STED) microscopy of proteins and synchrotron X-ray fluorescence (SXRF) imaging of trace metals, both performed with 40 nm spatial resolution, on primary rat hippocampal neurons. We achieve a detection limit for zinc of 14 zeptogram (10-21 g) per pixel. We reveal the co-localization at the nanoscale of zinc and tubulin in dendrites with a molecular ratio of about one zinc atom per tubulin-{beta} dimer. We observe the co-segregation of copper and F-actin within the nano-architecture of dendritic protrusions. In addition, zinc chelation causes a decrease in the expression of cytoskeleton proteins in dendrites and spines. Overall, these results indicate new functions for zinc and copper in the modulation of the cytoskeleton morphology in dendrites, a mechanism associated to neuronal plasticity and memory formation.

neuroscience↗

bioRxiv2019

High-resolution synchrotron imaging studies of intact fresh roots reveal soil bacteria promoted bioremediation and bio-fortification

Plant-microbe interactions can be utilized in bio-based processes such as bioremediation and biofortification, either to remove hazardous radionuclides and heavy metals from the soil, or to increase the accumulation of desired elements into crops to improve their quality. Optimizing such elegant plant-microbe interactions requires detailed understanding of the chemical element compositions of fresh plant tissues at cellular organelle resolution. However, such analyses remain challenging because conventional methods lack the required spatial resolution, contrast or sensitivity. Using a novel combination of nanoscaleresolution 3D cryogenic synchrotron-light ptychography, holotomography and fluorescence tomography, we show how soil bacteria interact with Arabidopsis thaliana and promote the uptake of various metals. Co-cultivation with Pseudomonas sp. strain T5-6-I alters root anatomy and increases levels of selenium (Se), iron (Fe) and other micronutrients in roots. Our approach highlights the interaction of plants and microbes in bioremediation and biofortification on the subcellular level.

plant biology↗

bioRxiv2019

Dense neuronal reconstruction through X-ray holographic nano-tomography

Elucidating the structure of neuronal networks provides a foundation for understanding how the nervous system processes information to generate behavior. Despite technological breakthroughs in visible light and electron microscopy, imaging dense nanometer-scale neuronal structures over millimeter-scale tissue volumes remains a challenge. Here, we demonstrate that X-ray holographic nano-tomography is capable of imaging large tissue volumes with sufficient resolution to disentangle dense neuronal circuitry in Drosophila melanogaster and mammalian central and peripheral nervous tissue. Furthermore, we show that automatic segmentation using convolutional neural networks enables rapid extraction of neuronal morphologies from these volumetric datasets. The technique we present allows rapid data collection and analysis of multiple specimens, and can be used correlatively with light microscopy and electron microscopy on the same samples. Thus, X-ray holographic nano-tomography provides a new avenue for discoveries in neuroscience and life sciences in general.

neuroscience↗