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Achim J Herrmann, Michelle M Gehringer
The oldest species of bacteria capable of oxygenic photosynthesis today are the freshwater Cyanobacteria Gloeobacter spp., belonging to the class Oxyphotobacteria. Several modern molecular evolutionary studies support the freshwater origin of cyanobacteria during the Archaean and their subsequent acquisition of salt tolerance mechanisms necessary for their expansion into the marine environment. This study investigated the effect of a sudden washout event from a freshwater location into either a brackish or marine environment on the photosynthetic efficiency of two unicellular freshwater cyanobacteria: the salt-tolerant Chroococcidiopsis thermalis PCC7203 and the cyanobacterial phylogenetic root species, Gloeobacter violaceus PCC7421...
March 15, 2019: Geobiology
Kuldeep D More, Liviu Giosan, Kliti Grice, Marco J L Coolen
Subsurface microbial communities are generally thought to be structured through in situ environmental conditions such as the availability of electron acceptors and donors and porosity, but recent studies suggest that the vertical distribution of a subset of subseafloor microbial taxa, which were present at the time of deposition, were selected by the paleodepositional environment. However, additional highly resolved temporal records of subsurface microbiomes and paired paleoenvironmental reconstructions are needed to justify this claim...
March 6, 2019: Geobiology
Shuichang Zhang, Xiaomei Wang, Huajian Wang, Christian J Bjerrum, Emma U Hammarlund, Emma R Haxen, Hanjie Wen, Yuntao Ye, Donald E Canfield
The Mesoproterozoic Era (1,600-1,000 million years ago, Ma) geochemical record is sparse, but, nevertheless, critical in untangling relationships between the evolution of eukaryotic ecosystems and the evolution of Earth-surface chemistry. The ca. 1,400 Ma Xiamaling Formation has experienced only very low-grade thermal maturity and has emerged as a promising geochemical archive informing on the interplay between climate, ecosystem organization, and the chemistry of the atmosphere and oceans. Indeed, the geochemical record of portions of the Xiamaling Formation has been used to place minimum constraints on concentrations of atmospheric oxygen as well as possible influences of climate and climate change on water chemistry and sedimentation dynamics...
March 6, 2019: Geobiology
Sylvie Bruggmann, Robert M Klaebe, Cora Paulukat, Robert Frei
The mollusc genus Mytilus is abundant in various modern marine environments and is an important substrate for palaeo-proxy work. The redox-sensitive chromium (Cr) isotope system is emerging as a proxy for changes in the oxidation state of the Earth's atmosphere and oceans. However, potential isotopic offsets between ambient sea water and modern biogenic carbonates have yet to be constrained. We measured Cr concentrations ([Cr]) and isotope variations (δ53 Cr) in recent mollusc shells (Mytilus) from open and restricted marine environments and compared these to ambient sea water δ53 Cr values...
February 21, 2019: Geobiology
Erik A Sperling, Sabrina Tecklenburg, Laramie E Duncan
No abstract text is available yet for this article.
February 12, 2019: Geobiology
Amber J M Jarrett, Grant M Cox, Jochen J Brocks, Emmanuelle Grosjean, Chris J Boreham, Dianne S Edwards
The ca. 1.38 billion years (Ga) old Roper Group of the McArthur Basin, northern Australia, is one of the most extensive Proterozoic hydrocarbon-bearing units. Organic-rich black siltstones from the Velkerri Formation were deposited in a deep-water sequence and were analysed to determine their organic geochemical (biomarker) signatures, which were used to interpret the microbial diversity and palaeoenvironment of the Roper Seaway. The indigenous hydrocarbon biomarker assemblages describe a water column dominated by bacteria with large-scale heterotrophic reworking of the organic matter in the water column or bottom sediment...
February 7, 2019: Geobiology
Mark A Torres, Sijia Dong, Kenneth H Nealson, A Joshua West
Silicate minerals represent an important reservoir of nutrients at Earth's surface and a source of alkalinity that modulates long-term geochemical cycles. Due to the slow kinetics of primary silicate mineral dissolution and the potential for nutrient immobilization by secondary mineral precipitation, the bioavailability of many silicate-bound nutrients may be limited by the ability of micro-organisms to actively scavenge these nutrients via redox alteration and/or organic ligand production. In this study, we use targeted laboratory experiments with olivine and the siderophore deferoxamine B to explore how microbial ligands affect nutrient (Fe) release and the overall rate of mineral dissolution...
February 7, 2019: Geobiology
Matthew A LeRoy, Benjamin C Gill
The later Cambrian Steptoean Positive Carbon Isotope Excursion (SPICE) event was an episode marked by pronounced changes to the global biogeochemical cycles of carbon and sulfur and significant extinctions on several paleocontinents including Laurentia (North America). While the exact cause(s) of these events remains debated, various lines of evidence suggest an increase in the areal extent of anoxia at the seafloor was a likely feature. Here, we explore whether changes in local oxygenation accompanied the onset of the SPICE in southern Laurentia using cores of the Nolichucky and Eau Claire Formations from Ohio and Kentucky, USA, that represent a transect into the Rome Trough/Conasauga intrashelf basin...
February 6, 2019: Geobiology
Nora Richter, William M Longo, Sarabeth George, Anna Shipunova, Yongsong Huang, Linda Amaral-Zettler
Members of the order Isochrysidales are unique among haptophyte lineages in being the exclusive producers of alkenones, long-chain ketones that are commonly used for paleotemperature reconstructions. Alkenone-producing haptophytes are divided into three major groups based largely on molecular ecological data: Group I is found in freshwater lakes, Group II commonly occurs in brackish and coastal marine environments, and Group III consists of open ocean species. Each group has distinct alkenone distributions; however, only Groups II and III Isochrysidales currently have cultured representatives...
February 5, 2019: Geobiology
Emily D Matys, Tyler Mackey, Christen Grettenberger, Elliott Mueller, Dawn Y Sumner, Ian Hawes, Roger E Summons
Bacteriohopanepolyols (BHPs) are bacterial membrane lipids that may be used as biological or environmental biomarkers. Previous studies have described the diversity, distribution, and abundance of BHPs in a variety of modern environments. However, the regulation of BHP production in polar settings is not well understood. Benthic microbial mats from ice-covered lakes of the McMurdo Dry Valleys, Antarctica provide an opportunity to investigate the sources, physiological roles, and preservation of BHPs in high-latitude environments...
February 1, 2019: Geobiology
Kevin Nguyen, Gordon D Love, J Alex Zumberge, Amy E Kelly, Jeremy D Owens, Megan K Rohrssen, Steven M Bates, Chunfang Cai, Timothy W Lyons
By about 2.0 billion years ago (Ga), there is evidence for a period best known for its extended, apparent geochemical stability expressed famously in the carbonate-carbon isotope data. Despite the first appearance and early innovation among eukaryotic organisms, this period is also known for a rarity of eukaryotic fossils and an absence of organic biomarker fingerprints for those organisms, suggesting low diversity and relatively small populations compared to the Neoproterozoic era. Nevertheless, the search for diagnostic biomarkers has not been performed with guidance from paleoenvironmental redox constrains from inorganic geochemistry that should reveal the facies that were most likely hospitable to these organisms...
January 10, 2019: Geobiology
Arne Sturm, David A Fowle, CarriAyne Jones, Karla Leslie, Sulung Nomosatryo, Cynthia Henny, Donald E Canfield, Sean A Crowe
This study evaluates rates and pathways of methane (CH4 ) oxidation and uptake using 14 C-based tracer experiments throughout the oxic and anoxic waters of ferruginous Lake Matano. Methane oxidation rates in Lake Matano are moderate (0.36 nmol L-1  day-1 to 117 μmol L-1  day-1 ) compared to other lakes, but are sufficiently high to preclude strong CH4 fluxes to the atmosphere. In addition to aerobic CH4 oxidation, which takes place in Lake Matano's oxic mixolimnion, we also detected CH4 oxidation in Lake Matano's anoxic ferruginous waters...
December 28, 2018: Geobiology
Jennifer Goff, Lee Terry, Joyabrata Mal, Kathrin Schilling, Céline Pallud, Nathan Yee
The dissolution of elemental selenium [Se(0)] during chemical weathering is an important step in the global selenium cycle. While microorganisms have been shown to play a key role in selenium dissolution in soils, the mechanisms of microbial selenium solubilization are poorly understood. In this study, we isolated a Bacillus species, designated as strain JG17, that exhibited the ability to dissolve Se(0) under oxic conditions and neutral pH. Growth of JG17 in a defined medium resulted in the production and accumulation of extracellular compounds that mediated Se(0) dissolution...
December 27, 2018: Geobiology
Joy Buongiorno, Fernando J Gomez, David A Fike, Linda C Kah
Environmental fluctuations are recorded in a variety of sedimentary archives of lacustrine depositional systems. Geochemical signals recovered from bottom sediments in closed-basin lakes are among the most sensitive paleoenvironmental indicators and are commonly used in reconstructing lake evolution. Microbialites (i.e., organosedimentary deposits accreted through microbial trapping and binding of detrital sediment or in situ mineral precipitation on organics [Palaios, 2, 1987, 241]), however, have been largely overlooked as paleoenvironmental repositories...
December 13, 2018: Geobiology
Graham Purvis, Cees van der Land, Naoko Sano, Charles Cockell, Anders Barlow, Peter Cumpson, Elisa Lopez-Capel, Neil Gray
Structures in geological samples are often interpreted as fossilised life; however, such interpretations are equivocal, as abiotic processes can be invoked to explain their presence. Thus, additional lines of chemical evidence are invaluable in confirming or refuting such morphological evidence. Glass shards in tuff from the Ontong Java Plateau (OJP) contain microtubular structures that are in close proximity to functionalised nitrogen substituted aromatic compounds that may be indicative of the chemical remnants of biological activity...
December 7, 2018: Geobiology
Toni L Cox, Han Ming Gan, John W Moreau
Subseafloor sulfate concentrations typically decrease with depth as this electron acceptor is consumed by respiring microorganisms. However, studies show that seawater can flow through hydraulically conductive basalt to deliver sulfate upwards into deeply buried overlying sediments. Our previous work on IODP Site C0012A (Nankai Trough, Japan) revealed that recirculation of sulfate through the subducting Philippine Sea Plate stimulated microbial activity near the sediment-basement interface (SBI). Here, we describe the microbial ecology, phylogeny, and energetic requirements of population of aero-tolerant sulfate-reducing bacteria in the deep subseafloor...
November 25, 2018: Geobiology
David T Flannery, Abigail C Allwood, Robert Hodyss, Roger Everett Summons, Michael Tuite, Malcolm R Walter, Kenneth H Williford
Ooids are accretionary grains commonly reported from turbulent, shallow-water environments. They have long been associated with microbially dominated ecosystems and often occur in close proximity to, or embedded within, stromatolites, yet have historically been thought to form solely through physicochemical processes. Numerous studies have revealed both constructive and destructive roles for microbes colonizing the surfaces of modern calcitic and aragonitic ooids, but there has been little evidence for the operation of these processes during the Archean and Proterozoic, when both ooids and microbially dominated ecosystems were more widespread...
November 18, 2018: Geobiology
Thomas A Laakso, Daniel P Schrag
The riverine supply of the globally limiting nutrient, phosphorus, to the ocean accounts for only a few percent of nutrient supply to photosynthetic organisms in surface waters. Recycling of marine organic matter by heterotrophic organisms provides almost all of the phosphorus that drives net primary production in the modern ocean. In the low-oxygen environments of the Proterozoic, the lack of free oxygen would have limited rates of oxic respiration, slowing the recycling of nutrients and thus limiting global rates of photosynthesis...
November 11, 2018: Geobiology
Tanai Cardona, Patricia Sánchez-Baracaldo, A William Rutherford, Anthony W Larkum
Photosystem II is a photochemical reaction center that catalyzes the light-driven oxidation of water to molecular oxygen. Water oxidation is the distinctive photochemical reaction that permitted the evolution of oxygenic photosynthesis and the eventual rise of eukaryotes. At what point during the history of life an ancestral photosystem evolved the capacity to oxidize water still remains unknown. Here, we study the evolution of the core reaction center proteins of Photosystem II using sequence and structural comparisons in combination with Bayesian relaxed molecular clocks...
November 9, 2018: Geobiology
Kyle A Marquart, Ben R Haller, Janet M Paper, Theodore M Flynn, Maxim I Boyanov, Ganiyat Shodunke, Colleen Gura, Qusheng Jin, Matthew F Kirk
Methanogenesis and iron reduction play major roles in determining global fluxes of greenhouse gases. Despite their importance, environmental factors that influence their interactions are poorly known. Here, we present evidence that pH significantly influences the balance between each reaction in anoxic environments that contain ferric (oxyhydr)oxide minerals. In sediment bioreactors that contained goethite as a source of ferric iron, both iron reduction and methanogenesis occurred but the balance between them varied significantly with pH...
November 1, 2018: Geobiology
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