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

Exploring microbial life in the multi-extreme environment of Dallol, Ethiopia

Early Earth and ExoEarths: origin and evolution of life (2017. Varsovia)The Danakil depression at the Afar region in Ethiopia is one of the most unique and extreme environments on Earth. At the confluence of three tectonic plates in the East African rift (Triple Afar Junction), the Afar Depression is the only place on Earth where the transition from continental to oceanic crust (rift-to drift process) can be observed on land. Several types of extreme environments co-exist in this area, including highly acidic hydrothermal springs linked to the local volcanic activity at the Dallol dome, as well as desert evaporites and hypersaline lakes that resulted from the intense evaporation of an ancient enclosed sea. Although there have been more than 50 years since the area was first explored, information about its chemistry and geology is limited, and its biology remains completely unknown. In January 2016 and in January 2017, after several years of preparation, we organized two interdisciplinary expeditions to the Dallol area in order to explore the presence of life and mineral-microbe interactions under these geochemical extremes. To do so, and in combination with geochemical and mineralogical studies, we are applying molecular analyses based on 16S rRNA gene sequences, metagenomic and cultural approaches. Here, we will present preliminary results on the presence of life and microbial diversity identified in several sites of this multi-extreme environment.Centre National de la Recherche Scientifique, Université Paris-Sud, FranciaLaboratoire de microbiologie des environnements extrêmes, Centre National de la Recherche Scientifique, Université de Bretagne Occidentale, FranciaDepartamento de Ecología, Universidad Autónoma de Madrid, EspañaUnidad de Baleares, Instituto Geológico y Minero de España, EspañaInstituto Andaluz de Ciencias de la Tierra, Consejo Superior de Investigaciones Científicas, EspañaInstituto Andaluz de Ciencias de la Tierra, Universidad de Granada, EspañaLaboratoire de Minéralogie, Physique des Matériaux et Cosmochimie , Centre National de la Recherche Scientifique, Université Pierre et Marie Curie, FranciaPeer reviewe

Hapalosiphonacean cyanobacteria (Nostocales) thrived amid emerging embryophytes in an early Devonian (407-million-year-old) landscape

Cyanobacteria have a long evolutionary history, well documented in marine rocks. They are also abundant and diverse in terrestrial environments; however, although phylogenies suggest that the group colonized land early in its history, paleontological documentation of this remains limited. The Rhynie chert (407 Ma), our best preserved record of early terrestrial ecosystems, provides an opportunity to illuminate aspects of cyanobacterial diversity and ecology as plants began to radiate across the land surface. We used light microscopy and super-resolution confocal laser scanning microscopy to study a new population of Rhynie cyanobacteria; we also reinvestigated previously described specimens that resemble the new fossils. Our study demonstrates that all are part of a single fossil species belonging to the Hapalosiphonaceae (Nostocales). Along with other Rhynie microfossils, these remains show that the accommodation of morphologically complex cyanobacteria to terrestrial ecosystems transformed by embryophytes was well underway more than 400 million years ago.Copyright © 2023 The Authors. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). The attached file is the published version of the article.NHM Repositor

Collective magnetotaxis of microbial holobionts is optimized by the three-dimensional organization and magnetic properties of ectosymbionts

International audienceOver the last few decades, symbiosis and the concept of holobiont—a host entity with a population of symbionts—have gained a central role in our understanding of life functioning and diversification. Regardless of the type of partner interactions, understanding how the biophysical properties of each individual symbiont and their assembly may generate collective behaviors at the holobiont scale remains a fundamental challenge. This is particularly intriguing in the case of the newly discovered magnetotactic holobionts (MHB) whose motility relies on a collective magnetotaxis (i.e., a magnetic field-assisted motility guided by a chemoaerotaxis system). This complex behavior raises many questions regarding how magnetic properties of symbionts determine holobiont magnetism and motility. Here, a suite of light-, electron- and X-ray-based microscopy techniques [including X-ray magnetic circular dichroism (XMCD)] reveals that symbionts optimize the motility, the ultrastructure, and the magnetic properties of MHBs from the microscale to the nanoscale. In the case of these magnetic symbionts, the magnetic moment transferred to the host cell is in excess (10 2 to 10 3 times stronger than free-living magnetotactic bacteria), well above the threshold for the host cell to gain a magnetotactic advantage. The surface organization of symbionts is explicitly presented herein, depicting bacterial membrane structures that ensure longitudinal alignment of cells. Magnetic dipole and nanocrystalline orientations of magnetosomes were also shown to be consistently oriented in the longitudinal direction, maximizing the magnetic moment of each symbiont. With an excessive magnetic moment given to the host cell, the benefit provided by magnetosome biomineralization beyond magnetotaxis can be questioned

Chrysolcolla Redefined as Spertiniite

XAFS and {mu}-XAFS spectra were collected at the Cu K-edge for seven chrysocolla samples (Peru, USA, and Congo). The results suggest that the local structure around Cu is similar to that in Cu(OH){sub 2} (spertiniite). Cu-L{sub 3} STXM imaging and spectroscopy confirm that the chrysocolla samples examined here consist of mesoscopic Cu(II)-rich domains surrounded by Si-rich domains (in agreement with results from infra-red spectroscopy). Hence, we suggest that chrysocolla, which is generally considered to be orthorhombic with composition (Cu,Al){sub 2}H{sub 2}Si{sub 2}O{sub 5}(OH){sub 4} {center_dot} nH{sub 2}O, is in actually a mesoscopic assemblage composed dominantly of spertiniite (Cu(OH){sub 2}), water and amorphous silica (SiO{sub 2})

Influence of Uranium on Bacterial Communities: A Comparison of Natural Uranium-Rich Soils with Controls

This study investigated the influence of uranium on the indigenous bacterial community structure in natural soils with high uranium content. Radioactive soil samples exhibiting 0.26% - 25.5% U in mass were analyzed and compared with nearby control soils containing trace uranium. EXAFS and XRD analyses of soils revealed the presence of U(VI) and uranium-phosphate mineral phases, identified as sabugalite and meta-autunite. A comparative analysis of bacterial community fingerprints using denaturing gradient gel electrophoresis (DGGE) revealed the presence of a complex population in both control and uranium-rich samples. However, bacterial communities inhabiting uraniferous soils exhibited specific fingerprints that were remarkably stable over time, in contrast to populations from nearby control samples. Representatives of Acidobacteria, Proteobacteria, and seven others phyla were detected in DGGE bands specific to uraniferous samples. In particular, sequences related to iron-reducing bacteria such as Geobacter and Geothrix were identified concomitantly with iron-oxidizing species such as Gallionella and Sideroxydans. All together, our results demonstrate that uranium exerts a permanent high pressure on soil bacterial communities and suggest the existence of a uranium redox cycle mediated by bacteria in the soil

The SuperCam Remote Sensing Instrument Suite for Mars 2020

International audienceThe Mars 2020 rover, essentially a structural twin of MSL, is being built to a) characterize the geology and history of a new landing site on Mars, b) find and characterize ancient habitable environments, c) cache samples for eventual return to Earth, and d) demonstrate in-situ production of oxygen needed for human exploration. Remote-sensing instrumentation is needed to support the first three of these goals [1]. The SuperCam instrument meets these needs with a range of instrumentation including the highest-resolution remote imaging on the rover, two different techniques for determining mineralogy , and one technique to provide elemental compositions. All of these techniques are co-boresighted, providing rapid comprehensive characterization. In addition, for targets within 7 meters of the rover the laser shock waves brush away the dust, providing cleaner surfaces for analysis. SuperCam will use an advanced version of the AEGIS robotic target selection software

Prokaryotic and Eukaryotic Community Structure in Field and Cultured Microbialites from the Alkaline Lake Alchichica (Mexico)

The geomicrobiology of crater lake microbialites remains largely unknown despite their evolutionary interest due to their resemblance to some Archaean analogs in the dominance of in situ carbonate precipitation over accretion. Here, we studied the diversity of archaea, bacteria and protists in microbialites of the alkaline Lake Alchichica from both field samples collected along a depth gradient (0–14 m depth) and long-term-maintained laboratory aquaria. Using small subunit (SSU) rRNA gene libraries and fingerprinting methods, we detected a wide diversity of bacteria and protists contrasting with a minor fraction of archaea. Oxygenic photosynthesizers were dominated by cyanobacteria, green algae and diatoms. Cyanobacterial diversity varied with depth, Oscillatoriales dominating shallow and intermediate microbialites and Pleurocapsales the deepest samples. The early-branching Gloeobacterales represented significant proportions in aquaria microbialites. Anoxygenic photosynthesizers were also diverse, comprising members of Alphaproteobacteria and Chloroflexi. Although photosynthetic microorganisms dominated in biomass, heterotrophic lineages were more diverse. We detected members of up to 21 bacterial phyla or candidate divisions, including lineages possibly involved in microbialite formation, such as sulfate-reducing Deltaproteobacteria but also Firmicutes and very diverse taxa likely able to degrade complex polymeric substances, such as Planctomycetales, Bacteroidetes and Verrucomicrobia. Heterotrophic eukaryotes were dominated by Fungi (including members of the basal Rozellida or Cryptomycota), Choanoflagellida, Nucleariida, Amoebozoa, Alveolata and Stramenopiles. The diversity and relative abundance of many eukaryotic lineages suggest an unforeseen role for protists in microbialite ecology. Many lineages from lake microbialites were successfully maintained in aquaria. Interestingly, the diversity detected in aquarium microbialites was higher than in field samples, possibly due to more stable and favorable laboratory conditions. The maintenance of highly diverse natural microbialites in laboratory aquaria holds promise to study the role of different metabolisms in the formation of these structures under controlled conditions