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Jérémie Aubineau, Abderrazak El Albani, Ernest Chi Fru, Murray Gingras, Yann Batonneau, Luis A Buatois, Claude Geffroy, Jérôme Labanowski, Claude Laforest, Laurent Lemée, Maria G Mángano, Alain Meunier, Anne-Catherine Pierson-Wickmann, Philippe Recourt, Armelle Riboulleau, Alain Trentesaux, Kurt O Konhauser
The 2.1-billion-year-old (Ga) Francevillian series in Gabon hosts some of the oldest reported macroscopic fossils of various sizes and shapes, stimulating new debates on the origin, evolution and organization of early complex life. Here, we document ten representative types of exceptionally well-preserved mat-related structures, comprising "elephant-skin" textures, putative macro-tufted microbial mats, domal buildups, flat pyritized structures, discoidal microbial colonies, horizontal mat growth patterns, wrinkle structures, "kinneyia" structures, linear patterns and nodule-like structures...
June 20, 2018: Geobiology
Anne E Otwell, Stephen J Callister, Robert W Sherwood, Sheng Zhang, Abby R Goldman, Richard D Smith, Ruth E Richardson
We established Fe(III)-reducing co-cultures of two species of metal-reducing bacteria, the Gram-positive Desulfotomaculum reducens MI-1 and the Gram-negative Geobacter sulfurreducens PCA. Co-cultures were given pyruvate, a substrate that D. reducens can ferment and use as electron donor for Fe(III) reduction. G. sulfurreducens relied upon products of pyruvate oxidation by D. reducens (acetate, hydrogen) for use as electron donor in the co-culture. Co-cultures reduced Fe(III) to Fe(II) robustly, and Fe(II) was consistently detected earlier in co-cultures than pure cultures...
June 15, 2018: Geobiology
Elif Koeksoy, Maximilian Halama, Nikolas Hagemann, Pascal R Weigold, Katja Laufer, Sara Kleindienst, James M Byrne, Anneli Sundman, Kurt Hanselmann, Itay Halevy, Ronny Schoenberg, Kurt O Konhauser, Andreas Kappler
As a consequence of Earth's surface oxygenation, ocean geochemistry changed from ferruginous (iron(II)-rich) into more complex ferro-euxinic (iron(II)-sulphide-rich) conditions during the Paleoproterozoic. This transition must have had profound implications for the Proterozoic microbial community that existed within the ocean water and bottom sediment; in particular, iron-oxidizing bacteria likely had to compete with emerging sulphur-metabolizers. However, the nature of their coexistence and interaction remains speculative...
June 9, 2018: Geobiology
Alexander Brasier, David Wacey, Mike Rogerson, Paul Guagliardo, Martin Saunders, Siri Kellner, Ramon Mercedes-Martin, Tim Prior, Colin Taylor, Anna Matthews, John Reijmer
Lacustrine carbonate chimneys are striking, metre-scale constructions. If these were bioinfluenced constructions, they could be priority targets in the search for early and extraterrestrial microbial life. However, there are questions over whether such chimneys are built on a geobiological framework or are solely abiotic geomorphological features produced by mixing of lake and spring waters. Here, we use correlative microscopy to show that microbes were living around Pleistocene Mono Lake carbonate chimneys during their growth...
June 9, 2018: Geobiology
Terry T Isson, Gordon D Love, Christopher L Dupont, Christopher T Reinhard, Alex J Zumberge, Dan Asael, Bleuenn Gueguen, John McCrow, Ben C Gill, Jeremy Owens, Robert H Rainbird, Alan D Rooney, Ming-Yu Zhao, Eva E Stueeken, Kurt O Konhauser, Seth G John, Timothy W Lyons, Noah J Planavsky
The biogeochemical cycling of zinc (Zn) is intimately coupled with organic carbon in the ocean. Based on an extensive new sedimentary Zn isotope record across Earth's history, we provide evidence for a fundamental shift in the marine Zn cycle ~800 million years ago. We discuss a wide range of potential drivers for this transition and propose that, within available constraints, a restructuring of marine ecosystems is the most parsimonious explanation for this shift. Using a global isotope mass balance approach, we show that a change in the organic Zn/C ratio is required to account for observed Zn isotope trends through time...
June 5, 2018: Geobiology
Motoko Igisu, Tadashi Yokoyama, Yuichiro Ueno, Satoru Nakashima, Mie Shimojima, Hiroyuki Ohta, Shigenori Maruyama
Aliphatic C-H bonds are one of the major organic signatures detected in Proterozoic organic microfossils, and their origin is a topic of interest. To investigate the influence of the presence of silica on the thermal alteration of aliphatic C-H bonds in prokaryotic cells during diagenesis, cyanobacteria Synechocystis sp. PCC6803 were heated at temperatures of 250-450°C. Changes in the infrared (IR) signals were monitored by micro-Fourier transform infrared (FTIR) spectroscopy. Micro-FTIR shows that absorbances at 2,925 cm-1 band (aliphatic CH2 ) and 2,960 cm-1 band (aliphatic CH3 ) decrease during heating, indicating loss of the C-H bonds, which was delayed by the presence of silica...
June 5, 2018: Geobiology
Claire R Cousins, Marilyn Fogel, Roxane Bowden, Ian Crawford, Adrian Boyce, Charles Cockell, Matthew Gunn
We investigated bacterial and archaeal communities along an ice-fed surficial hot spring at Kverkfjöll volcano-a partially ice-covered basaltic volcano at Vatnajökull glacier, Iceland, using biomolecular (16S rRNA, apsA, mcrA, amoA, nifH genes) and stable isotope techniques. The hot spring environment is characterized by high temperatures and low dissolved oxygen concentrations at the source (68°C and <1 mg/L (±0.1%)) changing to lower temperatures and higher dissolved oxygen downstream (34.7°C and 5...
June 1, 2018: Geobiology
Mario Giordano, Camilla Olivieri, Simona Ratti, Alessandra Norici, John A Raven, Andrew H Knoll
We report the results of simple experiments which support the hypothesis that changes in ocean chemistry beginning in the Mesozoic Era resulted in an increase in the nutritional quality per mole of C and per cell of planktonic algal biomass compared to earlier phytoplankton. We cultured a cyanobacterium, a diatom, a dinoflagellate, and a green alga in media mimicking aspects of the chemistry of Palaeozoic and Mesozoic-Cenozoic oceans. Substantial differences emerged in the quality of algal biomass between the Palaeozoic and Mesozoic-Cenozoic growth regimes; these differences were strongly affected by interspecific interactions (i...
May 30, 2018: Geobiology
K M Sutherland, S D Wankel, C M Hansel
The ability of micro-organisms to oxidize manganese (Mn) from Mn(II) to Mn(III/IV) oxides transcends boundaries of biological clade or domain. Many bacteria and fungi oxidize Mn(II) to Mn(III/IV) oxides directly through enzymatic activity or indirectly through the production of reactive oxygen species. Here, we determine the oxygen isotope fractionation factors associated with Mn(II) oxidation via various biotic (bacteria and fungi) and abiotic Mn(II) reaction pathways. As oxygen in Mn(III/IV) oxides may be derived from precursor water and molecular oxygen, we use a twofold approach to determine the isotope fractionation with respect to each oxygen source...
July 2018: Geobiology
D B Johnson, P A Beddows, T M Flynn, M R Osburn
Laguna Bacalar is a sulfate-rich freshwater lake on the Yucatan Peninsula that hosts large microbialites. High sulfate concentrations distinguish Laguna Bacalar from other freshwater microbialite sites such as Pavilion Lake and Alchichica, Mexico, as well as from other aqueous features on the Yucatan Peninsula. While cyanobacterial populations have been described here previously, this study offers a more complete characterization of the microbial populations and corresponding biogeochemical cycling using a three-pronged geobiological approach of microscopy, high-throughput DNA sequencing, and lipid biomarker analyses...
May 2018: Geobiology
Y Shen, V Thiel, J-P Duda, J Reitner
Eukaryotic steranes are typically absent or occur in very low concentrations in Precambrian sedimentary rocks. However, it is as yet unclear whether this may reflect low source inputs or a preservational bias. For instance, it has been proposed that eukaryotic lipids were profoundly degraded in benthic microbial mats that were ubiquitous prior to the advent of vertical bioturbation in the Cambrian ("mat-seal effect"). It is therefore important to test the microbial turnover and degradation of eukaryotic steroids in real-world microbial mats...
May 2018: Geobiology
C W Diamond, N J Planavsky, C Wang, T W Lyons
Despite a surge of recent work, the evolution of mid-Proterozoic oceanic-atmospheric redox remains heavily debated. Constraining the dynamics of Proterozoic redox evolution is essential to determine the role, if any, that anoxia played in protracting the development of eukaryotic diversity. We present a multiproxy suite of high-resolution geochemical measurements from a drill core capturing the ~1.4 Ga Xiamaling Formation, North China Craton. Specifically, we analyzed major and trace element concentrations, sulfur and molybdenum isotopes, and iron speciation not only to better understand the local redox conditions but also to establish how relevant our data are to understanding the contemporaneous global ocean...
May 2018: Geobiology
M Reinhardt, J-P Duda, M Blumenberg, C Ostertag-Henning, J Reitner, C Heim, V Thiel
Fossil derivatives of isorenieratene, an accessory pigment in brown-colored green sulfur bacteria, are often used as tracers for photic zone anoxia through Earth's history, but their diagenetic behavior is still incompletely understood. Here, we assess the preservation of isorenieratene derivatives in organic-rich shales (1.5-8.4 wt.% TOC) from two Lower Jurassic anoxic systems (Bächental oil shale, Tyrol, Austria; Posidonia Shale, Baden-Württemberg, Germany). Bitumens and kerogens were investigated using catalytic hydropyrolysis (HyPy), closed-system hydrous pyrolysis (in gold capsules), gas chromatography-mass spectrometry (GC-MS) and gas chromatography combustion isotope ratio-mass spectrometry (GC-C-IRMS)...
May 2018: Geobiology
R A Boyle, T W Dahl, C J Bjerrum, D E Canfield
Mixing of sediments by moving animals becomes apparent in the trace fossil record from about 550 million years ago (Ma), loosely overlapping with the tail end of the extreme carbonate carbon isotope δ13 Ccarbonate fluctuations that qualitatively distinguish the Proterozoic geochemical record from that of the Phanerozoic. These Precambrian-scale fluctuations in δ13 Ccarbonate (PSF-δ13 Ccarbonate ) remain enigmatic, due to their high amplitude and inclusion of global-scale negative δ13 Ccarbonate values, below anything attributable to mantle input...
May 2018: Geobiology
J Rouillard, J-M García-Ruiz, J Gong, M A van Zuilen
Archean hydrothermal environments formed a likely site for the origin and early evolution of life. These are also the settings, however, were complex abiologic structures can form. Low-temperature serpentinization of ultramafic crust can generate alkaline, silica-saturated fluids in which carbonate-silica crystalline aggregates with life-like morphologies can self-assemble. These "biomorphs" could have adsorbed hydrocarbons from Fischer-Tropsch type synthesis processes, leading to metamorphosed structures that resemble carbonaceous microfossils...
May 2018: Geobiology
M N Müller, A Krabbenhöft, H Vollstaedt, F P Brandini, A Eisenhauer
Marine calcifying eukaryotic phytoplankton (coccolithophores) is a major contributor to the pelagic production of CaCO3 and plays an important role in the biogeochemical cycles of C, Ca and other divalent cations present in the crystal structure of calcite. The geochemical signature of coccolithophore calcite is used as palaeoproxy to reconstruct past environmental conditions and to understand the underlying physiological mechanisms (vital effects) and precipitation kinetics. Here, we present the stable Sr isotope fractionation between seawater and calcite (Δ88/86 Sr) of laboratory cultured coccolithophores in individual dependence of temperature and seawater carbonate chemistry...
May 2018: Geobiology
J M Fulton, M A Arthur, B Thomas, K H Freeman
The carbon and nitrogen isotopic signatures of chloropigments and porphyrins from the sediments of redox-stratified lakes and marine basins reveal details of past biogeochemical nutrient cycling. Such interpretations are strengthened by modern calibration studies, and here, we report on the C and N isotopic composition of pigments and nutrients in the water column and surface sediment of redox-stratified Fayetteville Green Lake (FGL; New York). We also report δ13 C and δ15 N values for pyropheophytin a (Pphe a) and bacteriochlorophyll e (Bchl e) deposited in the Black Sea during its transition to a redox-stratified basin ca...
March 25, 2018: Geobiology
A Pace, R Bourillot, A Bouton, E Vennin, O Braissant, C Dupraz, T Duteil, I Bundeleva, P Patrier, S Galaup, Y Yokoyama, M Franceschi, A Virgone, P T Visscher
In modern stromatolites, mineralization results from a complex interplay between microbial metabolisms, the organic matrix, and environmental parameters. Here, we combined biogeochemical, mineralogical, and microscopic analyses with measurements of metabolic activity to characterize the mineralization processes and products in an emergent (<18 months) hypersaline microbial mat. While the nucleation of Mg silicates is ubiquitous in the mat, the initial formation of a Ca-Mg carbonate lamina depends on (i) the creation of a high-pH interface combined with a major change in properties of the exopolymeric substances at the interface of the oxygenic and anoxygenic photoautotrophic layers and (ii) the synergy between two major players of sulfur cycle, purple sulfur bacteria, and sulfate-reducing bacteria...
March 23, 2018: Geobiology
I Hawes, A D Jungblut, E D Matys, R E Summons
The Cryogenian (~717-636 Ma) is characterized by widespread glaciation and dramatic fluctuations in biogeochemical cycling during the Sturtian and Marinoan glaciations. The Snowball Earth hypothesis posits that during this period, ice-covered oceans of more or less global extent shut down or greatly diminished photosynthesis in the marine realm. However, rather than suffering a catastrophic loss of biodiversity, fossil evidence suggests that major eukaryotic lineages survived and, indeed, the end of the Cryogenian marks the onset of a rapid diversification of eukaryotic life...
March 12, 2018: Geobiology
C Magnabosco, K R Moore, J M Wolfe, G P Fournier
Phototrophic bacteria are among the most biogeochemically significant organisms on Earth and are physiologically related through the use of reaction centers to collect photons for energy metabolism. However, the major phototrophic lineages are not closely related to one another in bacterial phylogeny, and the origins of their respective photosynthetic machinery remain obscured by time and low sequence similarity. To better understand the co-evolution of Cyanobacteria and other ancient anoxygenic phototrophic lineages with respect to geologic time, we designed and implemented a variety of molecular clocks that use horizontal gene transfer (HGT) as additional, relative constraints...
March 2018: Geobiology
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