Preservation in microbial mats: mineralization by a talc-like phase of a fish embedded in a microbial sarcophagus

Frontiers in Earth Science 3 (2015): 51 This Document is Protected by copyright and was first published by Frontiers. All rights reserved. it is reproduced with permissionMicrobial mats have been repeatedly suggested to promote early fossilization of macroorganisms. Yet, experimental simulations of this process remain scarce. Here, we report results of 5 year-long experiments performed onfish carcasses to document the influence of microbial mats on mineral precipitation during early fossilization. Carcasses were initially placed on top of microbial mats. After 2 weeks, fish became coated by the mats forming a compact sarcophagus, which modified the microenvironment close to the corpses. Our results showed that these conditions favored the precipitation of a poorly crystalline silicate phase rich in magnesium. This talc-like mineral phase has been detected in three different locations within the carcasses placed in microbial mats for more than 4 years: (1) within inner tissues, colonized by several bacillary cells; (2) at the surface of bones of the upper face of the corpse buried in the mat; and (3) at the surface of several bones such as the dorsal fin which appeared to be gradually replaced by the Mg-silicate phase. This mineral phase has been previously shown to promote bacteria fossilization. Here we provide first experimental evidence that such Mg-rich phase can also be involved in exceptional preservation of animalsThis work, which is part of the research projects CGL2013-42643P and the research grant supporting MI were funded by the Spanish Ministry of Economy and Competitiveness. The SEM facility at IMPMC was supported by Region Ile de France grant SESAME 2006 I-07-593/R, INSU-CNRS, INP-CNRS, and University Pierre et Marie Curie, Paris. SEM analyses performed for this study were supported by a grant from the Foundation Simone et Cino Del Duca (PI: KB). We are also especially grateful to Olivier Beyssac for the help provided for RAMAN analysi

Metagenome-based diversity analyses suggest a significant contribution of non-cyanobacterial lineages to carbonate precipitation in modern microbialites

Frontiers in Microbiology 6 (2015): 797 This Document is Protected by copyright and was first published by Frontiers. All rights reserved. It is reproduced with permissionCyanobacteria are thought to play a key role in carbonate formation due to their metabolic activity, but other organisms carrying out oxygenic photosynthesis (photosynthetic eukaryotes) or other metabolisms (e.g., anoxygenic photosynthesis, sulfate reduction), may also contribute to carbonate formation. To obtain more quantitative information than that provided by more classical PCR-dependent methods, we studied the microbial diversity of microbialites from the Alchichica crater lake (Mexico) by mining for 16S/18S rRNA genes in metagenomes obtained by direct sequencing of environmental DNA. We studied samples collected at the Western (AL-W) and Northern (AL-N) shores of the lake and, at the latter site, along a depth gradient (1, 5, 10, and 15 m depth). The associated microbial communities were mainly composed of bacteria, most of which seemed heterotrophic, whereas archaea were negligible. Eukaryotes composed a relatively minor fraction dominated by photosynthetic lineages, diatoms in AL-W, influenced by Si-rich seepage waters, and green algae in AL-N samples. Members of the Gammaproteobacteria and Alphaproteobacteria classes of Proteobacteria, Cyanobacteria, and Bacteroidetes were the most abundant bacterial taxa, followed by Planctomycetes, Deltaproteobacteria (Proteobacteria), Verrucomicrobia, Actinobacteria, Firmicutes, and Chloroflexi. Community composition varied among sites and with depth. Although cyanobacteria were the most important bacterial group contributing to the carbonate precipitation potential, photosynthetic eukaryotes, anoxygenic photosynthesizers and sulfate reducers were also very abundant. Cyanobacteria affiliated to Pleurocapsales largely increased with depth. Scanning electron microscopy (SEM) observations showed considerable areas of aragonite-encrusted Pleurocapsa-like cyanobacteria at microscale. Multivariate statistical analyses showed a strong positive correlation of Pleurocapsales and Chroococcales with aragonite formation at macroscale, and suggest a potential causal link. Despite the previous identification of intracellularly calcifying cyanobacteria in Alchichica microbialites, most carbonate precipitation seems extracellular in this systemWe are grateful to Eleonor Cortés for help and good company during the field trip and to Eberto Novelo for helpful discussions at the UNAM lab. This research was funded by the European Research Council Grants ProtistWorld (PI PL-G., Grant Agreement no. 322669) and CALCYAN (PI KB, Grant Agreement no. 307110) under the European Union’s Seventh Framework Program and the RTP Génomique environnementale of the CNRS (project MetaStrom, PI DM

Cation Exchange in Smectites as a New Approach to Mineral Carbonation

Mineral carbonation of alkaline mine residues is a carbon dioxide removal (CDR) strategy that can be employed by the mining industry. Here, we describe the mineralogy and reactivity of processed kimberlites and kimberlite ore from Venetia (South Africa) and Gahcho Kué (Canada) diamond mines, which are smectite-rich (2.3–44.1 wt.%). Whereas, serpentines, olivines, hydrotalcites and brucite have been traditionally used for mineral carbonation, little is known about the reactivity of smectites to CO2. The smectite from both mines is distributed as a fine-matrix and is saponite, Mx/mm+Mg3(AlxSi4−x)O10(OH)2·nH2O, where the layer charge deficiency is balanced by labile, hydrated interlayer cations (Mm+). A positive correlation between cation exchange capacity and saponite content indicates that smectite is the most reactive phase within these ultramafic rocks and that it can be used as a source of labile Mg2+ and Ca2+ for carbonation reactions. Our work shows that smectites provide the fast reactivity of kimberlite to CO2 in the absence of the highly reactive mineral brucite [Mg(OH)2]. It opens up the possibility of using other, previously inaccessible rock types for mineral carbonation including tailings from smectite-rich sediment-hosted metal deposits and oil sands tailings. We present a decision tree for accelerated mineral carbonation at mines based on this revised understanding of mineralogical controls on carbonation potential

Study of modern lacustrine microbialites from Mexico : tracing biological activity and environmental conditions inducing their formation

Les microbialites sont des roches organo-sédimentaires dont les processus de formation restent mal compris. L'objectif central de cette thèse est de mieux comprendre les conditions environnementales permettant le développement de microbialites actuels provenant de 10 lacs volcaniques mexicains. Une grande diversité de compositions minéralogiques des microbialites a été observée, comprenant divers carbonates et la quasi omniprésence de silicates de magnésium authigènes. A partir de cette étude nous proposons une valeur minimale d'alcalinité permettant le développement des microbialites. De plus, une corrélation positive entre l'alcalinité et la teneur en sodium des lacs est apparue. Cette corrélation pourrait s'expliquer par des niveaux différents d'évaporation des lacs et/ou des degrés différents d'altération des silicates alentours. L'étude plus particulière des silicates de magnésium a révélé que ces phases sont faiblement cristallisées, semblables à la kérolite et ont un fort potentiel de fossilisation des microorganismes et de la matière organique. Ces silicates de magnésium sont parfois associés à du fer dont l'origine pose question dans ces environnements alcalins et oxygénés. Nous avons mis en évidence la présence de différents types de phases porteuses du fer : des hydroxydes doubles lamellaires (hydrotalcites), des oxy(hydroxy)des, des silicates de magnésium et des sulfures. Nous proposons plus spécifiquement que l'hydrotalcite pourrait être issue de l'altération des basaltes par la circulation de fluides souterrains et plus généralement que cette phase pourrait être un précurseur des silicates de magnésium abondamment observés dans les microbialites actuels.The processes leading to the formation of microbialites, which are organo-sedimentary rocks, are not well understood. The main goal of this thesis is to better understand the environmental conditions allowing the development of modern microbialites. Here we performed geochemical analyses of water solutions and mineralogical analyses of microbialites in 10 Mexican volcanic lakes. We found a large diversity of microbialites in terms of mineralogical composition, with occurrence of diverse carbonate phases as well as the frequent presence of authigenic magnesium silicate phases. From this study, we infer a minimum alkalinity value for the formation of lacustrine microbialites. Moreover, we observe a positive correlation between the alkalinity and the sodium content of the lakes. This may relate to variations in evaporation intensity and/or various degrees of weathering of the surrounding silicates. The study of Mg-silicates revealed that this phase is similar to kerolite, a poorly crystalline hydrated talc phase, and has a strong potential for the fossilization of microorganisms and organic matter. These silicates are sometimes associated with iron, the origin of which remains uncertain in these alkaline and oxidized environments. By the mineralogical study of several microbialites, we found several phases bearing iron: layered double hydroxides (hydrotalcites), Mg-silicates, oxy(hydroxi)des and sulfides. We propose more specifically that hydrotalcite could be the by-product of basalts weathering by groundwater. We propose more generally that hydrotalcite could be a precursor phase of Mg-silicates abundantly observed in modern microbialites

Etude de microbialites lacustres actuels du Mexique : traçage de l’activité biologique et des conditions environnementales de formation

The processes leading to the formation of microbialites, which are organo-sedimentary rocks, are not well understood. The main goal of this thesis is to better understand the environmental conditions allowing the development of modern microbialites. Here we performed geochemical analyses of water solutions and mineralogical analyses of microbialites in 10 Mexican volcanic lakes. We found a large diversity of microbialites in terms of mineralogical composition, with occurrence of diverse carbonate phases as well as the frequent presence of authigenic magnesium silicate phases. From this study, we infer a minimum alkalinity value for the formation of lacustrine microbialites. Moreover, we observe a positive correlation between the alkalinity and the sodium content of the lakes. This may relate to variations in evaporation intensity and/or various degrees of weathering of the surrounding silicates. The study of Mg-silicates revealed that this phase is similar to kerolite, a poorly crystalline hydrated talc phase, and has a strong potential for the fossilization of microorganisms and organic matter. These silicates are sometimes associated with iron, the origin of which remains uncertain in these alkaline and oxidized environments. By the mineralogical study of several microbialites, we found several phases bearing iron: layered double hydroxides (hydrotalcites), Mg-silicates, oxy(hydroxi)des and sulfides. We propose more specifically that hydrotalcite could be the by-product of basalts weathering by groundwater. We propose more generally that hydrotalcite could be a precursor phase of Mg-silicates abundantly observed in modern microbialites.Les microbialites sont des roches organo-sédimentaires dont les processus de formation restent mal compris. L'objectif central de cette thèse est de mieux comprendre les conditions environnementales permettant le développement de microbialites actuels provenant de 10 lacs volcaniques mexicains. Une grande diversité de compositions minéralogiques des microbialites a été observée, comprenant divers carbonates et la quasi omniprésence de silicates de magnésium authigènes. A partir de cette étude nous proposons une valeur minimale d'alcalinité permettant le développement des microbialites. De plus, une corrélation positive entre l'alcalinité et la teneur en sodium des lacs est apparue. Cette corrélation pourrait s'expliquer par des niveaux différents d'évaporation des lacs et/ou des degrés différents d'altération des silicates alentours. L'étude plus particulière des silicates de magnésium a révélé que ces phases sont faiblement cristallisées, semblables à la kérolite et ont un fort potentiel de fossilisation des microorganismes et de la matière organique. Ces silicates de magnésium sont parfois associés à du fer dont l'origine pose question dans ces environnements alcalins et oxygénés. Nous avons mis en évidence la présence de différents types de phases porteuses du fer : des hydroxydes doubles lamellaires (hydrotalcites), des oxy(hydroxy)des, des silicates de magnésium et des sulfures. Nous proposons plus spécifiquement que l'hydrotalcite pourrait être issue de l'altération des basaltes par la circulation de fluides souterrains et plus généralement que cette phase pourrait être un précurseur des silicates de magnésium abondamment observés dans les microbialites actuels

Geochemical Conditions Allowing the Formation of Modern Lacustrine Microbialites

International audienceInterpreting the environmental conditions of ancient microbialites rely on comparisons with modern analogues. Yet, we lack a detailed reference framework relating the chemical and mineralogical composition of modern lacustrine microbialites with the physical and chemical parameters prevailing in the lakes where they form. Here we performed geochemical analyses of water solutions and mineralogical analyses of microbialites in 12 Mexican crater lakes. We found a large diversity of microbialites in terms of mineralogical composition, with occurrence of diverse carbonate phases such as magnesian calcite, monohydrocalcite, aragonite, hydromagnesite, and dolomite as well as authigenic magnesium silicate phases. In parallel, the chemical compositions of the lakes differed particularly by their alkalinity, their concentration of ortho-silicic acid (H 4 SiO 4) and their Mg/Ca ratio. From this study, we infer a minimum alkalinity value for the formation of lacustrine microbialites, as well as several constraints given by the presence of mineral phases on the chemical composition of the lakes in which microbialites formed. Finally, we observe a general correlation between the alkalinity and the sodium content of the lakes. This may relate to variations in evaporation intensity and provide a historical model for lacustrine microbialite formation: microbialite start forming only when the lake is sufficiently old/evaporated

Importance of Prokaryotes in the Functioning and Evolution of the Present and Past Geosphere and Biosphere

International audienceThe purpose of this book is to show the essential and indispensable role of prokaryotes in the evolution of aliving world. The evolutionary success of prokaryotes is explained together with their role in the evolution of the geosphere, the biosphere and its functioning, as well as their ability to colonize all biotopes, including the most extreme ones. We consider that all past and present living beings emerged from prokaryotes and have interacted with them. Forces and mechanisms presented in the various theories of evolution apply to prokaryotes. The major stages of their evolution and biodiversity are also described. Finally, it is emphasized that prokaryotes are living organisms that provide indisputable evidence of evolutionary processes. Many examples of ongoing evolution in prokaryotes, observable at the human scale, are provided

Integrative analysis of the mineralogical and chemical composition of modern microbialites from ten Mexican lakes: What do we learn about their formation?

International audienceInterpreting the environmental conditions under which ancient microbialites formed relies upon comparisons with modern analogues. This is why we need a detailed reference framework relating the chemical and mineralogical compositions of modern microbialites to the physical and chemical parameters prevailing in the environments where they form. Here, we measured the chemical, including major and trace elements, and mineralogical composition of microbialites from ten Mexican lakes as well as the chemical composition of the surrounding waters. Saturation states of lakes with different mineral phases were systematically determined and correlations between solution and solid chemical analyses were assessed using multivariate analyses. A large diversity of microbialites was observed in terms of mineralogical composition, with occurrence of diverse carbonate phases such as (Mg-)calcite, monohydrocalcite, aragonite, hydromagnesite, and dolomite as well as authigenic Mg-silicate phases (kerolite and/or stevensite). All lakes harbouring microbialites were saturated or supersaturated with monohydrocalcite, suggesting that such a saturation state might be required for the onset of microbialite formation and that precursor soluble phases such as amorphous calcium carbonate and monohydrocalcite play a pivotal role in these lakes. Subsequently, monohydrocalcite transforms partly or completely to aragonite or Mg-calcite, depending on the lake (Mg/Ca)aq. Moreover, lakes harbouring hydromagnesite-containing microbialites were saturated with an amorphous magnesium carbonate phase, supporting again the involvement of precursor carbonate phases. Last, authigenic Mg-silicates formed by homogenous or heterogenous nucleation in lakes saturated or supersaturated with a phase reported in the literature as “amorphous sepiolite” and with a H4SiO4 concentration superior to 0.2 mM. A strong correlation between the alkalinity and the salinity of all the lakes was observed. The observed large variations of alkalinity between the lakes relate to varying concentration stages of an initial alkaline dilute water, due to a varying hydrochemical functioning. In all cases, the size of microbialites in the lakes correlated positively with salinity, (Mg/Ca)aq ratio and alkalinity. The trace element compositions of the microbialites also varied significantly between the lakes. Detrital contamination of the studied microbialites was the major factor affecting their rare earth elements (REE) + Y patterns. In particular, the microbialites highly affected by detrital contamination showed a high (REE + Y) content and flat (REE + Y) patterns. In contrast, some microbialites poorly affected by detrital contamination showed (REE + Y) patterns with features commonly reported for marine microbialites, such as a superchondritic Y/Ho ratio, enrichment in heavy REE and a negative Ce anomaly. This last observation questions the possibility to infer the marine versus lacustrine origin of a microbialite based on (REE + Y) patterns only. Overall, while microorganisms can impact nucleation processes and textural arrangements in microbialites, we observe that the hydrogeochemical evolution of lakes exerts a primary control over the onset of microbialite formation and the evolution of their chemical and mineralogical composition. Moreover, while changes of all these chemical and mineralogical features upon diagenesis and metamorphism will need to be assessed, the present study, together with recent meta-analyses of modern microbialites, broadens the set of modern references available for comparisons with geological archives