Aqueous electrocatalytic reduction of CO 2 into alcohol and hydrocarbon fuels presents a sustainable route towards energy-rich chemical feedstocks. Cu is the only material able to catalyse the substantial formation of multi-carbon products (C 2 /C 3), however competing proton reduction to hydrogen is an ever-present drain on selectivity. Herein, a superhydrophobic surface was generated by 1-octadecanethiol treatment of hierarchically structured Cu dendrites, inspired by the structure of gas-trapping cuticles on subaquatic spiders. The hydrophobic electrode attained 56% Faradaic efficiency for ethylene and 17% for ethanol production at neutral pH, compared to 9% and 4% on a hydrophilic, wettable equivalent. These observations are assigned to trapped gases at the hydrophobic Cu surface, which increase the concentration of CO 2 at the electrode|solution interface and consequently increase CO 2 reduction selectivity. Hydrophobicity is thus proposed as a governing factor in CO 2 reduction selectivity and can help explain trends seen on previously reported electrocatalysts.

Ecotoxicological effects of nanoparticles (NP) are still poorly documented while their commercialization for industrial and household applications increases. The aim of this study was to evaluate the influence of physicochemical characteristics on metal oxide NP and carbon nanotubes toxicological effects toward bacteria. Two strains of bacteria, Cupriavidus metallidurans CH34 and Escherichia coli MG1655 were exposed to TiO(2) or Al(2)O(3) NP or to multiwalled-carbon nanotubes (MWCNT). Particular attention was paid on optimizing NP dispersion to obtain nonagglomerated suspensions. Our results show that NP toxicity depends on their chemical composition, size, surface charge, and shape but not on their crystalline phase. MWCNT toxicity does not depend on their purity. Toxicity also depends on the bacterial strain: E. coli MG1655 is sensitive to NP, whereas C. metallidurans CH34 is not. Interestingly, NP are accumulated in both bacterial strains, and association between NP and bacteria is necessary for bacterial death to occur. NP may then represent a danger for the environment, causing the disappearance of some sensitive bacterial strains such as E. coli MG1655, but also being mobilized by nonsensitive strains such as C. metallidurans CH34 and transported through the whole ecosystem.

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Cyanobacteria have played a significant role in the formation of past and modern carbonate deposits at the surface of the Earth using a biomineralization process that has been almost systematically considered induced and extracellular. Recently, a deep-branching cyanobacterial species, Candidatus Gloeomargarita lithophora, was reported to form intracellular amorphous Ca-rich carbonates. However, the significance and diversity of the cyanobacteria in which intracellular biomineralization occurs remain unknown. Here, we searched for intracellular Cacarbonate inclusions in 68 cyanobacterial strains distributed throughout the phylogenetic tree of cyanobacteria. We discovered that diverse unicellular cyanobacterial taxa form intracellular amorphous Ca-carbonates with at least two different distribution patterns, suggesting the existence of at least two distinct mechanisms of biomineralization: (i) one with Ca-carbonate inclusions scattered within the cell cytoplasm such as in Ca. G. lithophora, and (ii) another one observed in strains belonging to the Thermosynechococcus elongatus BP-1 lineage, in which Ca-carbonate inclusions lie at the cell poles. This pattern seems to be linked with the nucleation of the inclusions at the septum of the cells, showing an intricate and original connection between cell division and biomineralization. These findings indicate that intracellular Ca-carbonate biomineralization by cyanobacteria has been overlooked by past studies and open new perspectives on the mechanisms and the evolutionary history of intra-and extracellular Ca-carbonate biomineralization by cyanobacteria.calcification | amorphous calcium carbonate | polyphosphate

Microbialites are sedimentary deposits associated with microbial mat communities and are thought to be evidence of some of the oldest life on Earth. Despite extensive studies of such deposits, little is known about the role of microorganisms in their formation. In addition, unambiguous criteria proving their biogenicity have yet to be established. In this study, we characterize modern calcareous microbialites from the alkaline Lake Van, Turkey, at the nanometer scale by combining x-ray and electron microscopies. We describe a simple way to locate microorganisms entombed in calcium carbonate precipitates by probing aromatic carbon functional groups and peptide bonds. Near-edge x-ray absorption fine structure spectra at the C and N K-edges provide unique signatures for microbes. Aragonite crystals, which range in size from 30 to 100 nm, comprise the largest part of the microbialites. These crystals are surrounded by a 10-nm-thick amorphous calcium carbonate layer containing organic molecules and are embedded in an organic matrix, likely consisting of polysaccharides, which helps explain the unusual sizes and shapes of these crystals. These results provide biosignatures for these deposits and suggest that microbial organisms significantly impacted the mineralogy of Lake Van carbonates.aragonite ͉ biosignature ͉ biomineralization ͉ spectromicroscopy L ake Van (eastern Anatolia, Turkey) is the largest soda lake on Earth, with a pH of 9.7-9.8 and a salinity of 21.7‰ (1). It harbors the largest known living microbialites, which are structures resulting from precipitation of aragonite at sites where calcium-rich groundwater seeps into the alkaline lake water (1, 2) and are associated with a wide diversity of microorganisms (3). Lake Van microbialites have a fine-grained micritic texture similar to most carbonate microbialites (4, 5) and consist of 30-to 100-nm-sized aragonite crystals (2, 3), which have morphologies that resemble bacteria-like forms (2). Some authors have suggested the possibility that nanospheres in microbialites could represent very small, entombed bacteria or ''nanobacteria'' (4, 5). However, the real nature of these carbonates, as well as their relationship to the microorganisms detected in the microbialites, remain unresolved.Because Lake Van is highly oversaturated with aragonite (1), the role of microorganisms in aragonite precipitation can be questioned, and the observed presence of microbes in these structures could simply result from passive trapping during mineral precipitation. This question is not new and has been raised systematically since the earliest studies of microbialites to the most recent ones (e.g., refs. 6-9). Some studies have demonstrated that microbes can actively mediate carbonate, in particular dolomite, precipitation (10). However, if passive trapping is operative, features suggesting that discrimination between microbially generated and purely abiotic precipitates is possible may be illusory. For example, the biogenicity of ancient stromatolites (i.e., laminated microbiali...

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[1] The phase relations and density of a natural mid-ocean ridge basalt (MORB) were investigated from 28 to 89 GPa and 1600 to 2700 K by in situ X-ray diffraction measurements and chemical analysis of the quenched samples using transmission electron microscopy (TEM). We observed an assemblage of five phases up to 50 GPa, namely an aluminum-bearing magnesium perovskite phase, a calcium perovskite phase, a stishovite phase, the new aluminum-rich (NAL) phase, and a calcium ferrite-type phase. The NAL phase was no longer observed above 50 GPa. The phase proportions were obtained by Rietveld refinement of the in situ X-ray diffraction patterns. After the disappearance of the NAL phase beyond 50 GPa, the proportion of each phase remains constant up to 89 GPa. The density of MORB was calculated using the measured volumes, phase proportions, and chemical compositions of the coexisting phases. The thermoelastic parameters of the MORB sample were estimated from the fit of the measured densities at various pressure and temperature conditions. Resulting MORB density profiles were calculated for different subducting slab temperature profiles. MORB densities are 0.5% to 2% greater than those of the surrounding mantle over the entire lower mantle range, suggesting MORB likely subducts to the core-mantle boundary.

The iron oxide mineral magnetite (Fe 3 O 4 ) is produced by various organisms to exploit magnetic and mechanical properties. Magnetotactic bacteria have become one of the best model organisms for studying magnetite biomineralization, as their genomes are sequenced and tools are available for their genetic manipulation. However, the chemical route by which magnetite is formed intracellularly within the so-called magnetosomes has remained a matter of debate. Here we used X-ray absorption spectroscopy at cryogenic temperatures and transmission electron microscopic imaging techniques to chemically characterize and spatially resolve the mechanism of biomineralization in those microorganisms. We show that magnetite forms through phase transformation from a highly disordered phosphate-rich ferric hydroxide phase, consistent with prokaryotic ferritins, via transient nanometric ferric (oxyhydr)oxide intermediates within the magnetosome organelle. This pathway remarkably resembles recent results on synthetic magnetite formation and bears a high similarity to suggested mineralization mechanisms in higher organisms.ferrihydrite | geomagnetism | hematite | nanoparticles | precursors