Unveiling billion-year old life forms with X-ray vision

An international team of scientists from Brazil, France and Switzerland with financial support from the Serrapilheira Institute and Fapesp, has obtained the most detailed 3D views ever achieved of very ancient traces of life on Earth. The studied microfossils, from the Gunflint Formation, in Canada, are approximately 1.9 billion years old, and are the preserved remains of microorganisms similar to bacteria existing today, but from a period when only microscopic life existed on Earth. Using an advanced imaging method based on synchrotron light, unprecedented details of the shape, composition and preservation of these microfossils was attained. Moreover, in one locality, fossils previously termed “hematite-coated” are revealed to be composed of organic material – invisible in optical microscopy – coated with crystals of the iron oxide maghemite, instead of hematite. This finding challenges our understanding of past life and opens exciting perspectives for the study of even older fossils or future samples returned from Mars.

Maldanis, L., Hickman-Lewis, K., Verezhak, M. et al. Nanoscale 3D quantitative imaging of 1.88 Ga Gunflint microfossils reveals novel insights into taphonomic and biogenic characters. Scientific Reports 10, 8163 (2020). https://doi.org/10.1038/s41598-020-65176-w

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3D observation of microfossils

Manganese: A double agent for imaging ?

Gadolinium (Gd3+) complexes have been used as MRI contrast agents for 35 years, but recently the safety of some was questioned. The replacement of Gd3+ by manganese (Mn2+), a biogenic metal, would enable safer complexes.

Nevertheless, the Mn2+ has to be chelated by complexes exhibiting high thermodynamic stability and kinetic inertness (to guarantee that the Mn is not released in vivo) and with a water molecule directly coordinated to the metal, essential for a good MRI efficiency. Combining these two properties is a chemistry challenge.

The “Metal complexes and MRI” team of CBM and their collaborators from IPHC (Strasbourg) have synthesized and studied a bispidine ligand, a molecule which cavity is well adapted for Mn2+ complexation. This Mn2+ complex has an excellent kinetic inertness and its MRI efficiency was validated by preclinical studies.

52Mn is an emergent radionuclide for positron emission tomography (PET). Mn2+ is the only metal enabling both MRI and PET imaging. The use of 52Mn is nevertheless limited by its low availability and lack of appropriate ligand.

For the first time in France, 52Mn was produced at the Orléans’ cyclotron, and 52Mn-bispidine was successfully obtained.

Overall, bispidine is a very promising ligand for the Mn2+ complexation, for MRI and PET. Due to its outstanding kinetic inertness, in vivo use of Mn2+ without toxicity risk can be anticipated.

 

See the news on the website of the CNRS Institute for Chemistry.

 

Eva Toth, Daouda Ndiaye, Maryame Sy, Agnès Pallier, Sandra Même, Isidro de Silva, Sara Lacerda, Aline M. Nonat, Loïc J. Charbonnière Unprecedented kinetic inertness for a Mn2+‐bispidine chelate: a novel structural entry for Mn2+‐based imaging agents - Angewandte Chemie, 2020, https://doi.org/10.1002/anie.202003685

Metallomics in geological time: trace element biosignatures evidence the influence of ocean chemistry on Earth’s earliest ecosystems

We used a combination of techniques: microbeam particle-induced X-ray emission spectroscopy (PIXE), carbon isotope geochemistry and electron microscopy. This has allowed us to discover trace element signatures of life in 3.33 billion-year-old rocks from South Africa. These signatures support a long-standing hypothesis that biological dependency on trace elements results from the enrichment of these elements in the metal-rich, hydrothermally influenced habitats of early life.

We approached this challenge through the biological concept of the metallome, which refers to the entirety of the inorganic species (metal and metalloid) within a cell. Although the genome and proteome do not survive fossilisation over billions of years, it is probable that metal concentrations within carbonaceous materials could do so, and indeed we found this to be the case in numerous carbon-rich microstructures from the Josefsdal Chert.

We found that a range of elements crucial to anaerobic microbes, including Fe, V, Ni, As and Co, were enriched within carbonaceous material characterised by negative carbon isotope signatures indicating biological origins.

Palaeo-metallome compositions could be used to deduce the metabolic networks of Earth’s earliest ecosystems and, potentially, as a biosignature for the evaluation of organic materials found on Mars.

The article “Metallomics in deep time and the influence of ocean chemistry on the metabolic landscapes of Earth’s earliest ecosystems” released March 18th in Scientific Reports.

Contact: keyron.hickman-lewis@cnrs.fr; frances.westall@cnrs.fr

 

DECLICS

On January 17, 2020, rich exchanges took place between the thematic group "Metal Complexes and MRI" and students of the first and final European class of the Lycée Pothier in Orleans as part of DECLICS "Dialogues Entre Chercheurs et Lycéens pour les Intéresser à la Construction des Savoirs" .