Biogeochemical Niche of Magnetotactic Cocci Capable of Sequestering Large Polyphosphate Inclusions in the Anoxic Layer of the Lake Pavin Water Column

Magnetotactic bacteria (MTB) are microorganisms thriving mostly at oxic–anoxic boundaries of aquatic habitats. MTB are efficient in biomineralising or sequestering diverse elements intracellularly, which makes them potentially important actors in biogeochemical cycles. Lake Pavin is a unique aqueous system populated by a wide diversity of MTB with two communities harbouring the capability to sequester not only iron under the form of magnetosomes but also phosphorus and magnesium under the form of polyphosphates, or calcium carbonates, respectively. MTB thrive in the water column of Lake Pavin over a few metres along strong redox and chemical gradients representing a series of different microenvironments. In this study, we investigate the relative abundance and the vertical stratification of the diverse populations of MTB in relation to environmental parameters, by using a new method coupling a precise sampling for geochemical analyses, MTB morphotype description, and in situ measurement of the physicochemical parameters. We assess the ultrastructure of MTB as a function of depth using light and electron microscopy. We evidence the biogeochemical niche of magnetotactic cocci, capable of sequestering large PolyP inclusions below the oxic–anoxic transition zone. Our results suggest a tight link between the S and P metabolisms of these bacteria and pave the way to better understand the implication of MTB for the P cycle in stratified environmental conditions.

Molluscs community as a keystone group for assessing the impact of urban sprawl at intertidal ecosystems

Mollusc communities are getting endangered in the aftermath of urban sprawl because artificial structures do not surrogate natural substrates. In this study, we compared the diversity, community and trophic arrangements of molluscs among different models of artificial substrate and their adjacent natural rock, to detect relationships between some abiotic variables and the mollusc communities. Complexity, chemical composition and age were tested as potential drivers of the community. Diversity, community and trophic structure differed between natural and artificial substrates. Complexity at the scale of cm was detected as the most important factor driving the community structure. In addition, a chemical composition based on silica and/or scarce calcium carbonates seems to be relevant for molluscs, as well as for the secondary substrate where they inhabit. However, age did not seem to be a driving factor. Among the different artificial structures, macroscale complexity was detected as the main factor diverging a drastically poor community at seawall from other artificial structures. In this context, macro and microscale complexity, chemical composition and mineral type are variables to consider in future designs of artificial substrates.

First Observation of Unicellular Organisms Concentrating Arsenic in ACC Intracellular Inclusions in Lake Waters

In unicellular organisms, intracellular inclusions of amorphous calcium carbonate (ACC) were initially described in cyanobacteria and, later, in unicellular eukaryotes from Lake Geneva (Switzerland/France). Inclusions in unicellular eukaryotes, named micropearls, consist of hydrated ACCs, frequently enriched in Sr or Ba, and displaying internal oscillatory zonations, due to variations in the Ba:Ca or Sr:Ca ratios. An analysis of our database, consisting of 1597 micropearl analyses from Lake Geneva and 34 from Lake Titicaca (Bolivia/Peru), showed that a certain number of Sr- and Ba-enriched micropearls from these lakes contain As in amounts measurable by EDXS. A Q-mode statistical analysis confirmed the existence of five chemically distinct morpho-chemical groups of As-bearing micropearls, among which was a new category identified in Lake Geneva, where As is often associated with Mg. This new type of micropearl is possibly produced in a small (7–12 μm size) bi-flagellated organism. Micropearls from Lake Titicaca, which contain Sr, were found in an organism very similar to Tetraselmis cordiformis, which was observed earlier in Lake Geneva. Lake Titicaca micropearls contain larger As amounts, which can be explained by the high As concentration in the water of this lake. The ubiquity of this observed biomineralization process points to the need for a better understanding of the role of amorphous or crystalline calcium carbonates in As cycling in surface waters.

Isotope geochemistry in archaeology

Isotope geochemistry is an important scientific technique that has made a significant contribution to archaeological research. Isotope techniques measure the relative abundance of a number of nuclides of the same (or derivative) element as a means of investigating a variety of natural processes. Both stable (H, O, C, N, Ca, Sr, Cu, Pb, S) and unstable (U, Th, K, Ar) isotope systems are analyzed as part of archaeological investigations.Isotopes (often referred to as a nuclide in the singular) are variants of a particular element, which share the same number of protons but have varying numbers of neutrons. Isotopes are referred to as stable or unstable, depending on whether they undergo radioactive decay. Some nuclides are primordial, meaning they have existed since the beginning of the universe, while others are the product of the decay of other elements. Isotopes of the same element generally share the same chemical behavior.Stable isotopes can be applied to studying a variety of processes with their applicability to specific problems depending on the mechanism by which one nuclide becomes naturally enriched or depleted. The basis of the application of some stable isotopes is that the variation in their atomic mass leads them to behave differently during processes such as evaporation, precipitation, freezing, photosynthesis, and incorporation into the body. Another approach is based on taking advantage of the varying abundance of some stable isotopes within different geological units to allow proveniencing of various materials. This can only be achieved if the isotope ratios remain unchanged after incorporation into the sample.Unstable isotopes are most commonly used as a geochronological tool for establishing the age of materials such as organics, calcium carbonates, and igneous rocks. Unstable nuclides that have either too many or too few neutrons spontaneously transform by beta decay, alpha decay, or spontaneous nuclear fission. The decay speed can be calibrated to time and is usually expressed as a “half-life.” On the basis of a known decay rate and original abundance ratio, the comparison of the relative abundance of a stable nuclide to an unstable nuclide can provide an age estimation of the material studied. In the case of radiocarbon dating, the abundance of 14C in the sample is compared to modern levels of 14C.Isotope analysis can be performed directly on archaeological materials or on geological materials to provide a context for archaeological sites. A particular advantage of using isotopic methods in archaeological investigations is that it provides quantifiable information that can be compared to the material culture record.

Composition of microorganisms in carbonated mineral waters of the Mukhen deposit (Khabarovsk territory)

The chemical composition, distribution, structure, number of physiological groups of cultivated bacteria and their biodiversity in the cold carbonic mineral waters of Mukhen and in microbial mats were studied. It is shown that the mineral waters are cold, hydrocarbonate-calcium-magnesium, enriched with iron, manganese, barium. Carbon dioxide predominates in the gaseous composition of waters. Microbiological studies have shown that no sanitary-indicative microflora was found in mineral waters, which indicates the purity of underground waters. Carbonic waters were characterized by a low number of physiological groups of autochthonous bacteria. Among the studied microorganisms, chemolithotrophic thionic bacteria predominated, which indicates the predominance of oxidation processes of reduced sulfur compounds with the participation of bacteria in groundwater. In the microbial mats, various chemolithotrophic and heterotrophic microorganisms were identified, participating in the geochemical cycles of carbon, nitrogen, sulfur, iron, manganese, and silicon. The number of physiological groups of bacteria was higher than in mineral waters, along with this saprophytic bacteria predominated significantly. A sufficiently high rate of protein and cellulose decomposition by microorganisms of microbial mats was shown. A low diversity of cultured heterotrophic bacteria with the dominance of microorganisms of the genus Bacillus was found in mineral waters and in microbial mats. By using the methods of X-ray phase analysis, the important role of microorganisms of microbial mats in the precipitation of silicate minerals and the formation of calcium carbonates was shown.

Durability of UHPFRC functionalised with nanoadditives due to synergies in the action of sulphate and chloride in cracked and uncracked states

This paper studies the durability of Ultra High Performance Fibre Reinforced Concrete (UHPFRC) with high Blast Furnace Slag content (BFS) and nanoadditives such as crystalline admixture (CA), alumina nanofibres (ANF) and cellulose nanocrystals (CNC), exposed to different aggressive environmental conditions: 1) three aggressive media: a) deionized water (dw), b) sulphate rich solution (ss) and c) simulated geothermal water (sgw) containing sulphate and chloride; 2) two water interaction conditions: a) static and b) dynamic (water impact); and 3) with and without the presence of cracks. Durability was analysed over 24 months, measuring several physical and chemical parameters of the system, recording changes in both the aggressive media and the concrete. All UHPFRC types demonstrate good durability, showing high resistance to expansion and deformation in the sulphate-rich media. A leaching process occurs in all water interaction systems, the dynamic interaction in sgw being the most aggressive. The interaction of sgw inside the crack favours the formation of solid phases such as calcium carbonates and ettringite, while the presence of nanoadditives affects the response of both the matrix and the formation of precipitates within the crack.

Molluscs Community as a Keystone Group for Assessing the Impact of Urban Sprawl at Intertidal Ecosystems

Mollusc communities are getting endangered as a result of urban sprawl because artificial structures do not surrogate natural substrates. In this study, we compared diversity and community and trophic structures of molluscs among different models of artificial substrate and its adjacent natural rock, to detect relationships between some abiotic variables and the molluscs community. Complexity, chemical composition and age were tested as potential drivers of the community. Diversity, community and trophic structure differed between natural and artificial substrates. Complexity at the scale of cm was detected as the most important factor driving community structure. Besides, a chemical composition based on silica and/or scarce calcium carbonates seems to be relevant for molluscs, as well as for the secondary substrate where they inhabit. However, age did not seem to be a driving factor. Among the different artificial structures, macroscale complexity was detected as the main factor diverging a drastically poor community at seawalls from other artificial structures.

First Observation of Unicellular Organisms Concentrating Arsenic in ACC Intracellular Inclusions

In unicellular organisms, intracellular inclusions of amorphous calcium carbonate (ACC) have been initially described in cyanobacteria and, later, in unicellular eukaryotes of Lake Geneva (Switzerland/France). Inclusions in unicellular eukaryotes ‒named micropearls‒ consist of hydrated ACCs, frequently enriched in Sr or Ba, displaying internal oscillatory zonations due to variations in the Ba:Ca or Sr:Ca ratios. The analysis of our database consisting of 1597 micropearl analyses from Lake Geneva and 34 from Lake Titicaca (Bolivia/Peru) has shown that a certain number of Sr and Ba-enriched micropearls from these lakes contain As in amounts measurable by EDXS. A Q-mode statistical analysis has confirmed the existence of five geochemically distinct morpho-chemical groups of As-bearing micropearls, among which a new category identified in Lake Geneva, where As is often associated with Mg. This new type of micropearl is possibly produced in a small (7-12 m size) bi-flagellated organism. Micropearls from Lake Titicaca, which contain Sr, are found in an organism very similar to Tetraselmis cordiformis, observed in Lake Geneva. Lake Titicaca micropearls contain higher As concentrations which can be explained by the high As concentration in the water of this lake. The ubiquity of the biomineralization process observed points to the need for better understanding of the role of amorphous or crystalline calcium carbonates in As cycling in surface waters.

The Influence of Aqueous Se(IV) on the Stability of Different CaCO3 Polymorphs Precipitated under Ambient Conditions

Selenium is an essential bio-element, but because of its bioaccumulation potential, it can become toxic and is an important pollutant. The ubiquitous mineral calcite (CaCO3) has the ability to immobilize anions as SeO32− by different sorption or coprecipitation processes. Experimental studies have found that SeO32− can incorporate in the crystal structure of calcite by substituting CO32−. The presence of foreign ions in aqueous solution strongly affects CaCO3 precipitation, helping stabilize less stable polymorphs such as vaterite and aragonite or hydrated phases. In this work, we studied the aging process of calcium carbonates precipitated from aqueous solutions highly supersaturated with respect to CaCO3 and slightly supersaturated with respect to CaSeO3·H2O under ambient conditions, for times up to 30 days in which solids were kept in the remaining aqueous solution. Under these conditions, CaCO3 precipitated mainly as low crystallinity vaterite aggregates that hosted up to 16% atomic ratio Se:C. Vaterite purified and increased its crystallinity with aging time, but the vaterite–calcite transformation was strongly inhibited. The incorporation of Se(IV) in vaterite did not significantly affect the cell parameters or the external morphology of the aggregates. The precipitation of selenite as CaSeO3·H2O was conditioned by the availability of free Ca2+ and SeO32− that was not previously incorporated into precipitated carbonates.

A new gene family diagnostic for intracellular biomineralization of amorphous Ca-carbonates by cyanobacteria

Cyanobacteria have massively contributed to carbonate deposit formation over the geological history. They are traditionally thought to biomineralize CaCO3 extracellularly as an indirect byproduct of photosynthesis. However, the recent discovery of freshwater cyanobacteria forming intracellular amorphous calcium carbonates (iACC) challenges this view. Despite the geochemical interest of such a biomineralization process, its molecular mechanisms and evolutionary history remain elusive. Here, using comparative genomics, we identify a new gene (ccyA) and protein (calcyanin) family specifically associated with cyanobacterial iACC biomineralization. Calcyanin is composed of a conserved C-terminal domain, which likely adopts an original fold, and a variable N- terminal domain whose structure allows differentiating 4 major types among the 35 known calcyanin homologues. Calcyanin lacks detectable full-length homologs with known function. Yet, genetic and comparative genomic analyses suggest a possible involvement in Ca homeostasis, making this gene family a particularly interesting target for future functional studies. Whatever its function, this new gene family appears as a gene diagnostic of intracellular calcification in cyanobacteria. By searching for ccyA in publicly available genomes, we identified 13 additional cyanobacterial strains forming iACC. This significantly extends our knowledge about the phylogenetic and environmental distribution of cyanobacterial iACC biomineralization, especially with the detection of multicellular genera as well as a marine species. Phylogenetic analyses indicate that iACC biomineralization is ancient, with independent losses in various lineages and some HGT cases that resulted in the broad but patchy distribution of calcyanin across modern cyanobacteria. Overall, iACC biomineralization emerges as a new case of genetically controlled biomineralization in bacteria.