Low‐Fe(III) Greenalite Was a Primary Mineral From Neoarchean Oceans

Banded iron formations (BIFs) represent chemical precipitation from Earth’s early oceans and therefore contain insights into ancient marine biogeochemistry. However, BIFs have undergone multiple episodes of alteration, making it difficult to assess the primary mineral assemblage. Nanoscale mineral inclusions from 2.5 billion year old BIFs and ferruginous cherts provide new evidence that iron silicates were primary minerals deposited from the Neoarchean ocean, contrasting sharply with current models for BIF inception. Here we used multiscale imaging and spectroscopic techniques to characterize the best preserved examples of these inclusions. Our integrated results demonstrate that these early minerals were low‐Fe(III) greenalite. We present potential pathways in which low‐Fe(III) greenalite could have formed through changes in saturation state and/or iron oxidation and reduction. Future constraints for ancient ocean chemistry and early life’s activities should include low‐Fe(III) greenalite as a primary mineral in the Neoarchean ocean.Plain Language SummaryChemical precipitates from Earth’s early oceans hold clues to ancient seawater chemistry and biological activities, but we first need to understand what the original minerals were in ancient marine deposits. We characterized nanoscale mineral inclusions from 2.5 billion year old banded iron formations and determined that the primary minerals were iron‐rich silicate minerals dominated by reduced iron, challenging current hypotheses for banded iron formation centered on iron oxides. Our results suggest that our planet at this time had a very reducing ocean and further enable us to present several biogeochemical mineral formation hypotheses that can now be tested to better understand the activities of early life on ancient Earth.Key PointsNeoarchean nanoparticle silicate inclusions appear to be the earliest iron mineral preserved in cherts from Australia and South AfricaOur multiscale analyses indicate that the particles are greenalite that are dominantly Fe(II) with have low and variable Fe(III) contentWe present four (bio)geochemical hypotheses that could produce low‐Fe(III) greenalitePeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143747/1/grl57046_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/143747/2/grl57046.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/143747/3/grl57046-sup-0001-2017GL076311-SI.pd

Will tomorrow's mineral materials be grown?

Abstract Biomineralization, the capacity to form minerals, has evolved in a great diversity of bacterial lineages as an adaptation to different environmental conditions and biological functions. Microbial biominerals often display original properties (morphology, composition, structure, association with organics) that significantly differ from those of abiotically formed counterparts, altogether defining the ‘mineral phenotype’. In principle, it should be possible to take advantage of microbial biomineralization processes to design and biomanufacture advanced mineral materials for a range of technological applications. In practice, this has rarely been done so far and only for a very limited number of biomineral types. This is mainly due to our poor understanding of the underlying molecular mechanisms controlling microbial biomineralization pathways, preventing us from developing bioengineering strategies aiming at improving biomineral properties for different applications. Another important challenge is the difficulty to upscale microbial biomineralization from the lab to industrial production. Addressing these challenges will require combining expertise from environmental microbiologists and geomicrobiologists, who have historically been working at the forefront of research on microbe–mineral interactions, alongside bioengineers and material scientists. Such interdisciplinary efforts may in the future allow the emergence of a mineral biomanufacturing industry, a critical tool towards the development more sustainable and circular bioeconomies

Review Article -Petrology, Geochemistry Why do microbes make minerals?

International audienceProkaryotes have been shaping the surface of the Earth and impacting geochemical cycles for the past four billion years. Biomineralization, the capacity to form minerals, is a key process by which microbes interact with their environment. While we keep improving our understanding of the mechanisms of this process ("how?"), questions around its functions and adaptive roles ("why?") have been less intensively investigated. Here, we discuss biomineral functions for several examples of prokaryotic biomineralization systems, and propose a roadmap for the study of microbial biomineralization through the lens of adaptation. We also discuss emerging questions around the potential roles of biomineralization in microbial cooperation and as important components of biofilm architectures. We call for a shift of focus from mechanistic to adaptive aspects of biomineralization, in order to gain a deeper comprehension of how microbial communities function in nature, and improve our understanding of life co-evolution with its mineral environment

Organic stabilization of extracellular elemental sulfur in a Sulfurovum-rich biofilm: a new role for extracellular polymeric substances?

This work shines light on the role of extracellular polymeric substance (EPS) in the formation and preservation of elemental sulfur biominerals produced by sulfur-oxidizing bacteria. We characterized elemental sulfur particles produced within a Sulfurovum-rich biofilm in the Frasassi Cave System (Italy). The particles adopt spherical and bipyramidal morphologies, and display both stable (α-S8) and metastable (β-S8) crystal structures. Elemental sulfur is embedded within a dense matrix of EPS, and the particles are surrounded by organic envelopes rich in amide and carboxylic groups. Organic encapsulation and the presence of metastable crystal structures are consistent with elemental sulfur organomineralization, i.e., the formation and stabilization of elemental sulfur in the presence of organics, a mechanism that has previously been observed in laboratory studies. This research provides new evidence for the important role of microbial EPS in mineral formation in the environment. We hypothesize that the extracellular organics are used by sulfur-oxidizing bacteria for the stabilization of elemental sulfur minerals outside of the cell wall as a store of chemical energy. The stabilization of energy sources (in the form of a solid electron acceptor) in biofilms is a potential new role for microbial EPS that requires further investigation

Microscopy evidence of bacterialmicrofossils in phosphorite crusts of the Peruvian shelf: Implications for phosphogenesis mechanisms

International audiencePhosphorites are sedimentary formations enriched in Ca-phosphate minerals. The precipitation of these minerals is thought to be partlymediated by the activity of microorganisms. The vast majority of studies on phosphorites have focused on a petrological and geochemical characterization of these rocks. However, detailed descriptions are needed at the sub-micrometer scale atwhich crucial information can be retrieved about traces of past ormodern microbial activities. Here, scanning electron microscopy (SEM) analyses of a recent phosphorite crust from the upwelling-style phosphogenesis area off Peru revealed that it contained a great number of rod-like and coccus-like shaped micrometer-sized (~1.1 μm and 0.5 μm, respectively) objects, referred to as biomorphs. Some of these biomorphs were filled with carbonate fluoroapatite (CFA, a calcium-phosphate phase common in phosphorites); some were empty; some were surrounded by one or two layers of pyrite. Transmission electron microscopy (TEM) and energy dispersive X-ray spectrometry (EDXS) analyses were performed on focused ion beam(FIB)milled ultrathin foils to characterize the texture of CFA and pyrite in these biomorphs at the fewnanometer scale. Non-pyritized phosphatic biomorphswere surrounded by a thin (5-15 nmthick) rimappearing as a void on TEM images. Bundles of CFA crystals sharing the same crystallographic orientations (aligned along their c-axis) were found in the interior of some biomorphs. Pyrite formed a thick (~35-115 nm) layer with closely packed crystals surrounding the pyritized biomorphs, whereas pyrite crystals at distance from the biomorphs were smaller and distributed more sparsely. Scanning transmission X-ray microscopy (STXM) analyses performed at the C K-edge provided maps of organic and inorganic carbon in the samples. Inorganic C, mainly present as carbonate groups in the CFA lattice, was homogeneously distributed, whereas organic C was concentrated in the rims of the phosphatic biomorphs. Finally, STXM analyses at the Fe L2,3-edges together with TEMEDXS analyses, revealed that some pyritized biomorphs experienced partial oxidation. The mineralogical features of these phosphatic biomorphs are very similar to those formed by bacteria having precipitated phosphate minerals intra- and extracellularly in laboratory experiments. Similarly, pyritized biomorphs resemble bacteria encrusted by pyrite. We therefore interpret phosphatic and pyritized biomorphs present in the Peruvian phosphorite crust as microorganisms fossilized near the boundary of zones of sulfate reduction. The implications of these observations are then discussed in the light of the different possible and non-exclusive microbiallydriven phosphogenesis mechanisms that have been proposed in the past: (i) Organic matter mineralization, in particular mediated by iron reducing bacteria and/or sulfate-reducing bacteria (SRB), (ii) reduction of iron- (oxyhydr)oxides by iron-reducing bacteria and/or SRB, and (iii) polyphosphate metabolism in sulfide-oxidizing bacteria, possibly associated with SR

Characterization of Ca-phosphate biological materials by scanning transmission x-ray microscopy (STXM) at the Ca L 2,3 -, P L 2,3 -and C K- edges

International audienceSeveral naturally occurring biological materials, including bones and teeth, pathological calcifications, microbial mineral deposits formed in marine phosphogenesis areas, as well as bio-inspired cements used for bone and tooth repair are composed of Ca-phosphates. These materials are usually identified and characterized using bulk-scale analytical tools such as X-ray diffraction, Fourier transform infrared spectroscopy or nuclear magnetic resonance. However, there is a need for imaging techniques that provide information on the spatial distribution and chemical composition of the Ca-phosphate phases at the micrometer- and nanometer scales. Such analyses provide insightful indications on how the materials may have formed, e.g. through transient precursor phases that eventually remain spatially separated from the mature phase. Here, we present scanning transmission X-ray microscopy (STXM) analyses of Ca-phosphate reference compounds, showing the feasibility of fingerprinting Ca-phosphate-based materials. We calibrate methods to determine important parameters of Ca-phosphate phases, such as their Ca/P ratio and carbonate content at the ∼25 nm scale, using X-ray absorption near-edge spectra at the C K-, Ca L2,3- and P L2,3-edges. As an illustrative case study, we also perform STXM analyses on hydroxyapatite precipitates formed in a dense fibrillar collagen matrix. This study paves the way for future research on Ca-phosphate biomineralization processes down to the scale of a few tens of nanometers

A re-examination of the mechanism of whiting events: a new role for diatoms in Fayetteville Green Lake (New York, USA)

Whiting events—the episodic precipitation of fine-grained suspended calcium carbonates in the water column—have been documented across a variety of marine and lacustrine environments. Whitings likely are a major source of carbonate muds, a constituent of limestones, and important archives for geochemical proxies of Earth history. While several biological and physical mechanisms have been proposed to explain the onset of these precipitation events, no consensus has been reached thus far. Fayetteville Green Lake (New York, USA) is a meromictic lake that experiences annual whitings. Materials suspended in the water column collected through the whiting season were characterized using scanning electron microscopy and scanning transmission X-ray microscopy. Whitings in Fayetteville Green Lake are initiated in the spring within the top few meters of the water column, by precipitation of fine amorphous calcium carbonate (ACC) phases nucleating on microbial cells, as well as on abundant extracellular polymeric substances (EPS) frequently associated with centric diatoms. Whiting particles found in the summer consist of 5–7 μm calcite grains forming aggregates with diatoms and EPS. Simple calculations demonstrate that calcite particles continuously grow over several days, then sink quickly through the water column. In the late summer, partial calcium carbonate dissolution is observed deeper in the water column. Settling whiting particles, however, reach the bottom of the lake, where they form a major constituent of the sediment, along with diatom frustules. The role of diatoms and associated EPS acting as nucleation surfaces for calcium carbonates is described for the first time here as a potential mechanism participating in whitings at Fayetteville Green Lake. This mechanism may have been largely overlooked in other whiting events in modern and ancient environments

Impact of biomineralization on the preservation of microorganisms during fossilization: An experimental perspective

International audienceThe biogenicity of fossil microbial biomorphs is often debated because their morphologies are poorly informative and the chemical, structural and isotopic signatures of putative biogenic organic molecules have been altered during their incorporation into the sediments and the geological history of the host rock. Here, we investigated the effect of encrustation by biominerals on the morphological and chemical degradation of Escherichia coli cells during experimental thermal treatments. Non-calcified E. coli cells and E. coli cells encrusted by calcium phosphates were exposed to heating under an Argon atmosphere at two different temperatures (300 ◦C, 600 ◦C) for 20 h. Two additional experiments were performed on noncalcified E. coli cells at 300 ◦C for 2 h and 100 h to discuss the influence of experiment duration. Organic residues of all experiments were characterized at a multiple length scale using a combination of scanning electron microscopy, transmission electron microscopy, Raman microspectroscopy, electron paramagnetic resonance (EPR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and X-ray absorption near edge structure spectroscopy (XANES) at the carbon K edge. In the absence of encrusting biominerals, the morphological structure of the organic residues of E. coli cells was completely lost after heating at 300 or 600 ◦C, even after short (2 h long) heating experiments. The content of aromatic functional groups of the organic residues of non-calcified E. coli cells increased during heat-treatment at 600 ◦C for 20 h while the amide functional groups were lost, as indicated by FT-IR spectroscopy. Consistently, the EPR spectrum of these organic residues indicated important transformation. As a comparison, this spectrum appeared similar to EPR spectra of ancient organic carbons such as carbons from the Apex chert (ca. 3460 Myr), indicating a similar concentration of aromatic moieties. In contrast, calcified E. coli exposed to the same conditions showed only limited morphological alteration as observed by electron microscopy as well as lower chemical transformation as detected by FT-IR and EPR spectroscopies. Despite the difficulties to relate experimental conditions directly to geological conditions, these experiments evidence the influence of cell encrustation by minerals on their chemical and morphological preservation potential during fossilization processe

Quantification of the ferric/ferrous iron ratio in silicates by scanning transmission X-ray microscopy at the Fe L2,3 edges

International audienceEstimation of Fe3?/RFe ratios in materials at the submicrometre scale has been a long-standing challenge in the Earth and environmental sciences because of the usefulness of this ratio in estimating redox conditions as well as for geothermometry. To date, few quantitative methods with submicrometric resolution have been developed for this purpose, and most of them have used electron energy-loss spectroscopy carried out in the ultra-high vacuum environment of a transmission electron microscope (TEM). Scanning transmission X-ray microscopy (STXM) is a relatively new technique complementary to TEM and is increasingly being used in the Earth sciences. Here, we detail an analytical procedure to quantify the Fe3?/RFe ratio in silicates using Fe L2,3-edge X-ray absorption near edge structure (XANES) spectra obtained by STXM, and we discuss its advantages and limitations. Two different methods for retrieving Fe3?/RFe ratios from XANES spectra are calibrated using reference samples with known Fe3? content by independent approaches. The first method uses the intensity ratio of the two major peaks at the L3-edge. This method allows mapping of Fe3?/RFe ratios at a spatial scale better than 50 nm by the acquisition of 5 images only. The second method employs a 2-eV-wide integration window centred on the L2 maximum for Fe3?, which is compared to the total integral intensity of the Fe L2-edge. These two approaches are applied to metapelites from the Glarus massif (Switzerland), containing micrometre- sized chlorite and illite grains and prepared as ultrathin foils by focused ion beam milling. Nanometrescale mapping of iron redox in these samples is presented and shows evidence of compositional zonation. The existence of such zonation has crucial implications for geothermometry and illustrates the importance of being able to measure Fe3?/RFe ratios at the submicrometre scale in geological samples