Biology subjects

Chevrier, D. M.

Publications and source records attributed to Chevrier, D. M..

3 recordsLinked to original sources

bioRxiv2026

Magnetic organelle gene clusters enable bacterial growth and ATP homeostasis under oxidizing conditions

Biological organisms can produce magnetic nanoparticles made of magnetite to detect the Earth's magnetic field for orientation. The evolutionary mechanisms that led to the acquisition of this capacity remain unknown. The most ancient organisms known to perform magnetic orientation are magnetotactic bacteria. Under tight genetic control, they produce chains of magnetite nanoparticles in dedicated organelles to allow efficient navigation in aquatic environments containing molecular oxygen. Yet, these bacteria have been proposed to emerge before molecular oxygen became abundant on Earth, at a time when this navigation system could not have served its current function. Here, we show that gene clusters responsible of magnetite formation and organization enable resistance against hydrogen peroxide, a toxic oxygen-derived compound that was produced during the early stages of Earth's oxygenation when iron oxidation consumed molecular oxygen. Characterization of the nanoparticle's oxidation state supported the involvement of magnetite in resistance to hydrogen peroxide-induced oxidative stress. These findings are compatible with an early emergence of magnetotactic bacteria, before natural waters became oxygenated. We propose a conceptual framework to explain the origin of magnetic orientation in bacteria, and offer tools to identify the initiation of Earth's oxygenation in a time-resolved manner.

microbiology↗

bioRxiv2026

The metallome of Methanosarcina barkeri during electron uptake from acathode

Electromethanogenesis, the cathode-dependent reduction of CO2 to CH4 by methanogens, offers a sustainable route to methane fuel. Methanosarcina barkeri lacks surface-exposed multiheme cytochromes for extracellular electron transfer (EET). Instead, we recently showed that surface-bound G-quadruplex ribonucleic acids (G4-RNA) are required for EET, yet how electrons traverse this extracellular matrix remains unresolved. Here, we quantified metal accumulation during cathodic growth by inductively coupled plasma mass spectrometry in cells grown on cathodes poised at -430 mV versus the standard hydrogen electrode, using acetate-grown cells, open-circuit controls and abiotic cathodes for comparison. Cathode-grown M. barkeri showed CH4 buildup attributable to cathodic electrons (2.1 {+/-} 0.8% CH4), whereas open-circuit controls showed negligible increase (0.26 {+/-} 0.15% CH4). Cathode-bound cells exhibited [~]55-fold enrichment in Co, Ni and Mo, and 5- to 21-fold enrichment in Cu, Zn, and Fe relative to acetate-grown cells; neither acetate-grown cells nor abiotic cathodes accumulated metals. To resolve where metals reside, we mapped the elemental distribution in acetate-grown cells by scanning transmission electron microscopy-energy dispersive X-ray spectroscopy and high-resolution nano X-ray fluorescence. Fe co-localized with phosphorus in intracellular storage bodies, whereas Co and Zn localized within the extracellular capsule. Together, these data indicate selective metal sequestration during electromethanogenesis and raise the possibility that certain metals associate with G4-RNA and/or the methanochondroitin matrix to support charge transfer at the cell surface. This metalomic fingerprint provides a new proxy for dissecting archaeal EET strategies and may inform the design of more efficient bioelectrochemical systems.

microbiology↗

bioRxiv2024

Dynamic change of calcium-rich compartments during coccolithophore biomineralization

Coccolithophores are abundant marine phytoplankton that produce biomineralized calcite scales, called coccoliths, which sequester substantial amounts of carbon and play a significant role in biogeochemical cycles. However, mechanisms underlying the storage and transport of ions essential for calcification remain unresolved. We used ptychographic X-ray computed tomography under cryogenic conditions to visualize intracellular calcium-rich structures involved in the storage of calcium ions in the coccolithophore species Chrysotila carterae. During calcification, we observed a range of structures, from small electron-dense bodies within larger compartments, to denser and distributed globular compartments, before returning to small bodies once scale formation is complete. Nanobeam-scanning X-ray fluorescence measurements further revealed these electron-dense bodies are rich in P and Ca (molar ratio of [~]4:1). We infer from the dynamic nature of structures that these bodies are part of required cellular calcium ion transport pathways, a fundamental process critical for understanding the response of coccolithophores to climate change.

cell biology↗