Probing elemental and structural heterogeneities is essential for understanding how materials evolve and degrade, yet correlating chemical and structural information across mesoscale specimens at the nanoscale remains analytically challenging. Here, we introduce a nondestructive correlative workflow that combines three-dimensional data sets from nanoscale X-ray ptychographic and fluorescence tomographies acquired on the same sample at dedicated synchrotron instruments. This workflow was developed and applied to quantify metal traces within individual low-Z compartments of a whole 1.88-billion-year-old Gunflint microfossil exhibiting a distinctive nanoscale architecture characteristic of thick-walled Huroniospora. Beyond the thick wall containing pluri-micrometer-sized quartz crystals with nanoinclusions, our analyses reveal an extracellular shell composed of submicrometer-sized quartz and Fe2+-rich greenalite embedded within an Fe3+-rich chert matrix. The specimen is unfractured and contains organic matter comparable to that of modern bacterial cells of similar volume. The trace sensitivity achieved in the multimetal three-dimensional maps, combined with precise volumetric quantification at nanometer scales, enabled accurate determination of metal concentrations in fossil compartments. Iron and manganese levels comparable to those of extant photosynthetic microorganisms, together with manganese-calcium-enriched iron silicate cores, suggest a cyanobacterial lineage and provide new insights into early microbial metabolisms. This correlative workflow, enabling high-sensitivity multielement trace analysis of low-Z nanostructured mesoscopic systems without physical subsampling, is broadly transferable to applications ranging from biominerals and geobiological materials to advanced functional materials such as catalysts, batteries, and nanocomposites.

The chemotaxis response of E. coli to metal cations is less understood than their response to organic molecules. Using dark-field videomicroscopy, E. coli behavior was analyzed in a 17 mm-long microfluidic channel exposed to a Zn(NO3)2 chemorepellent gradient, generated by a 250 mM solution placed in a well at the channel extremity, with or without prior Zn2+ pre-exposure of the cultures (10 µM). The bacteria exhibited an escape wave away from the zinc source. Compared to unexposed cultures, zinc pre-exposure resulted in a constant and shorter passage time at a given position of the wave peak, despite unchanged growth and swimming speed. The time lag decreased with growth duration. Given the one-dimensional gradient setup, this decrease is associated to a reduced diffusion duration from the Zn2⁺ source. The content of Zn2⁺ in the extracellular medium at the peak of the wave is therefore lower, but allows bacteria to escape more rapidly. These findings suggested an increase in bacterial Zn2⁺ sensitivity. By analogy to Ni2⁺ binding to the cytoplasmic HAMP domain of the Tar receptor, Zn2⁺ likely triggers a chemorepellent response through a cytoplasmic receptor. The activation of this receptor relies on the available zinc pool, which is specifically buffered by substantial other intracellular zinc reservoirs. In this model, saturating the reservoirs in pre-exposed cultures would enable the fastest response time, and a gradual filling of the reservoirs in unexposed cells would reduce a delay in chemotactic escape.

This chapter (Nano‐Imaging for Advanced X‐ray Fluorescence and Absorption Spectroscopy Applications) is a contribution to the Geostandards and Geoanalytical Research Handbook of Rock and Mineral Analysis – an online textbook that is a fully revised and updated edition of A Handbook of Silicate Rock Analysis (P. J. Potts, 1987, Blackie, Glasgow). Chapter 16 (from Section 3 of the handbook devoted to microbeam techniques) has been designed to provide a coherent progression, starting with a brief introduction of the essential fundamentals and the practical information needed to understand the experimental specifics of nano‐XRF imaging. This concise yet crucial information is followed by a comprehensive presentation of current applications of nano‐XRF imaging, with examples showcasing elemental measurement and XAS applications based on nano‐XRF imaging. To conclude, the final section offers a brief overview of emerging perspectives that should be of particular interest to young researchers at the beginning of their careers.

Understanding the nature and preservation of microbial traces in extreme environments is crucial for reconstructing Earth's early biosphere and for the search for life on other planets or moons. At Rio Tinto, southwestern Spain, ferric oxide and sulfate deposits similar to those discovered at Meridiani Planum, Mars, entomb a diversity of fossilized organisms, despite chemical conditions commonly thought to be challenging for life and fossil preservation. Investigating this unique fossil microbiota can elucidate ancient extremophile communities and the preservation of biosignatures in acidic environments on Earth and, potentially, Mars. In this study, we use an innovative multiscale approach that combines the state-of-the-art synchrotron X-ray nanoimaging methods of ptychographic X-ray computed laminography and nano-X-ray fluorescence to reveal Rio Tinto's microfossils at subcellular resolution. The unprecedented nanoscale views of several different specimens within their geological and geochemical contexts reveal novel intricacies of preserved microbial communities. Different morphotypes, ecological interactions, and possible taxonomic affinities were inferred based on qualitative and quantitative 3D ultrastructural information, whereas diagenetic processes and metabolic affinities were inferred from complementary chemical information. Our integrated nano-to-microscale analytical approach revealed previously invisible microbial and mineral interactions, which complemented and filled a gap of spatial resolution in conventional methods. Ultimately, this study contributes to the challenge of deciphering the faint chemical and morphological biosignatures that can indicate life's presence on the early Earth and on distant worlds.

Flagellar swimming hydrodynamics confers a recognized advantage for attachment on solid surfaces. Whether this motility further enables the following environmental cues was experimentally explored. Motile E. coli (OD 0.1) in a 100 µm-thick channel were exposed to off-equilibrium gradients set by a chemorepellent Ni(NO3)2-source (250 mM). Single bacterial dynamics at the solid surface was analyzed by dark-field videomicroscopy at a fixed position. The number of bacteria indicated their congregation into a wave escaping from the repellent source. Besides the high velocity drift in the propagation direction within the wave, an unexpectedly high perpendicular component drift was also observed. Swimming hydrodynamics CW-bends the bacteria trajectories during their primo approach to the surface (< 2 µm), and a high enough tumbling frequency likely preserves a notable lateral drift. This comprehension substantiates a survival strategy tailored to toxic environments, which involves drifting along surfaces, promoting the inception of colonization at the most advantageous sites.

Future long-duration human spaceflights require developments to limit biocontamination of surface habitats. The three MATISS (Microbial Aerosol Tethering on Innovative Surfaces in the International Space Station) campaigns exposed surface treatments over several months in the ISS. To this end, eight sample holders designed were mounted with lamella-bearing FDTS ((1H, 1H, 2H, 2H)-perfluorodecyltrichlorosilane), SiOCH, and parylene hydrophobic coatings, at two different locations, for several months, during three distinct periods from 2016 to 2020. Tile scanning optical microscopy (×3 and ×30 magnifications) detected several thousand particles, indicating a relatively clean environment (a few particles per mm2). In previous studies, exposure rates were analyzed for all the coarse and fine particles detected on the largest total area of the integrated FDTS area exposed in the ISS (several cm2). Here, the contamination rates observed for a smaller constant area unit (the 0.66-cm2 window area of the holder) were statistically analyzed. Therefore, a statistical difference in rate distributions between RGSH (Return Grid Sensor House) and EDR (European Drawer Rack) and between FDTS and either SiOCH or parylene was shown for the coarse particles but not for the fine particles. The contamination rates were found to be low, confirming the efficiency of the long-term air purification system. The rates tend to vary with the astronaut occupancy rates. Surfaces of spacecraft for long-duration exploration left unmanned during dormancy periods can be considered safe from biocontamination.

Future long-duration human spaceflight will require developments to limit biocontamination of surface habitats. The MATISS (Microbial Aerosol Tethering on Innovative Surfaces in the international Space Station) experiments allowed for exposing surface treatments in the ISS (International Space Station) using a sample-holder developed to this end. Three campaigns of FDTS (perFluoroDecylTrichloroSilane) surface exposures were performed over monthly durations during distinct periods. Tile scanning optical microscopy (×3 and ×30 magnifications) showed a relatively clean environment with a few particles on the surface (0.8 to 7 particles per mm 2 ). The varied densities and shapes in the coarse area fraction (50–1500 µm 2 ) indicated different sources of contamination in the long term, while the bacteriomorph shapes of the fine area fraction (0.5–15 µm 2 ) were consistent with microbial contamination. The surface contamination rates correlate to astronauts’ occupancy rates on board. Asymmetric particles density profiles formed throughout time along the air-flow. The higher density values were located near the flow entry for the coarse particles, while the opposite was the case for the fine particles, probably indicating the hydrophobic interaction of particles with the FDTS surface.

Oldest microfossils with methane-based metabolism in a subsurface environment expand the frontiers of early Earth habitability. Subsurface habitats on Earth host an extensive extant biosphere and likely provided one of Earth’s earliest microbial habitats. Although the site of life’s emergence continues to be debated, evidence of early life provides insights into its early evolution and metabolic affinity. Here, we present the discovery of exceptionally well-preserved, ~3.42-billion-year-old putative filamentous microfossils that inhabited a paleo-subseafloor hydrothermal vein system of the Barberton greenstone belt in South Africa. The filaments colonized the walls of conduits created by low-temperature hydrothermal fluid. Combined with their morphological and chemical characteristics as investigated over a range of scales, they can be considered the oldest methanogens and/or methanotrophs that thrived in an ultramafic volcanic substrate.

20 years of Quarantine Extraterrestrial Sample Analyses methodology ALEXANDRE S SIMIONOVICI1, LAURENCE LEMELLE2, PIERRE BECK3, FRANCOIS FIHMAN4, TOM SCHOONJANS5, REMI TUCOULOU TACHOUERES6, LARA MALDANIS7, KATERYNA KIRYUKHINA8 AND MICHEL VISO8 1University Grenoble Alpes 2LGL-TPE, ENS de Lyon, Université de Lyon, CNRS 3IPAG, Univ. Grenoble Alpes 46TEC 5Rosalind Franklin Institute 6European Synchrotron Radiation Facility 7Université Grenoble Alpes 8CNES Presenting Author: alexandre.simionovici@univ-grenoblealpes.fr

Oldest microfossils with methane-based metabolism in a subsurface environment expand the frontiers of early Earth habitability.

Subsurface habitats on Earth host an extensive extant biosphere and likely provided one of Earth’s earliest microbial habitats. Although the site of life’s emergence continues to be debated, evidence of early life provides insights into its early evolution and metabolic affinity. Here, we present the discovery of exceptionally well-preserved, ~3.42-billion-year-old putative filamentous microfossils that inhabited a paleo-subseafloor hydrothermal vein system of the Barberton greenstone belt in South Africa. The filaments colonized the walls of conduits created by low-temperature hydrothermal fluid. Combined with their morphological and chemical characteristics as investigated over a range of scales, they can be considered the oldest methanogens and/or methanotrophs that thrived in an ultramafic volcanic substrate.

Oldest microfossils with methane-based metabolism in a subsurface environment expand the frontiers of early Earth habitability.

Subsurface habitats on Earth host an extensive extant biosphere and likely provided one of Earth's earliest microbial habitats. Although the site of life's emergence continues to be debated, evidence of early life provides insights into its early evolution and metabolic affinity. Here, we present the discovery of exceptionally well-preserved, similar to 3.42-billion-year-old putative filamentous microfossils that inhabited a paleo-subseafloor hydrothermal vein system of the Barberton greenstone belt in South Africa. The filaments colonized the walls of conduits created by low-temperature hydrothermal fluid. Combined with their morphological and chemical characteristics as investigated over a range of scales, they can be considered the oldest methanogens and/or methanotrophs that thrived in an ultramafic volcanic substrate.

Sub-cellular trace element quantifications of nano-heterogeneities in brain tissues offer unprecedented ways to explore at elemental level the interplay between cellular compartments in neurodegenerative pathologies. We designed a quasi-correlative method for analytical nanoimaging of the substantia nigra , based on transmission electron microscopy and synchrotron X-ray fluorescence. It combines ultrastructural identifications of cellular compartments and trace element nanoimaging near detection limits, for increased signal-to-noise ratios. Elemental composition of different organelles is compared to cytoplasmic and nuclear compartments in dopaminergic neurons of rat substantia nigra . They exhibit 150–460 ppm of Fe, with P/Zn/Fe-rich nucleoli in a P/S-depleted nuclear matrix and Ca-rich rough endoplasmic reticula. Cytoplasm analysis displays sub-micron Fe/S-rich granules, including lipofuscin. Following AAV-mediated overexpression of α-synuclein protein associated with Parkinson’s disease, these granules shift towards higher Fe concentrations. This effect advocates for metal (Fe) dyshomeostasis in discrete cytoplasmic regions, illustrating the use of this method to explore neuronal dysfunction in brain diseases.

Bacteria tumble periodically, following environmental cues. Whether they can tumble near a solid surface is a basic issue for the inception of infection or mineral biofouling. Observing freely swimming Escherichia coli near and parallel to a glass surface imaged at high magnification (×100) and high temporal resolution (500 Hz), we identified tumbles as events starting (or finishing, respectively) in abrupt deceleration (or reacceleration, respectively) of the body motion. Selected events show an equiprobable clockwise (CW) or counterclockwise change in direction that is superimposed on a surface CW path because of persistent propulsion. These tumbles follow a common long (about 300 ± 100 ms, N = 52) deceleration-reorientation-acceleration pattern. A wavelet transform multiscale analysis shows these tumbles cause in-plane diffusive reorientations with 1.5 rad2/s rotational diffusivity, a value that compares with that measured in bulk tumbles. In half of the cases, additional few-millisecond bursts of an almost equiprobable CW or counterclockwise change of direction (12 ± 90°, N = 89) occur within the reorientation stage. The highly dispersed absolute values of change of direction (70 ± 66°, N = 89) of only a few bursts destabilize the cell-swimming direction. These first observations of surface tumbles set a foundation for statistical models of run-and-tumble surface motion different from that in bulk and lend support for chemotaxis near solid surface.