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Shinnosuke Aoyama, Yuichiro Ueno
Microbial sulfate reduction is among the most ubiquitous metabolic processes on earth. The oldest evidence of microbial sulfate reduction appears in the ca. 3.5 Ga Dresser Formation in the North Pole area of Pilbara Craton in Western Australia. That evidence was found through analysis of quadruple sulfur isotopes of sulfate and sulfide minerals deposited on the seafloor. However, the activity of microbial sulfate reduction below the Archean seafloor remains poorly understood. Here, we report the quadruple sulfur isotopic compositions of sulfide minerals within hydrothermally altered seafloor basalt and less altered basaltic komatiite collected from the North Pole Dome area...
December 15, 2017: Geobiology
N J Butterfield
No abstract text is available yet for this article.
November 11, 2017: Geobiology
L G Tarhan, N J Planavsky, X Wang, E J Bellefroid, M L Droser, J G Gehling
The paleoenvironmental setting in which the Ediacara Biota lived, died, and was preserved in the eponymous Ediacara Member of the Rawnsley Quartzite of South Australia is an issue of long-standing interest and recent debate. Over the past few decades, interpretations have ranged from deep marine to shallow marine to terrestrial. One of the key features invoked by adherents of the terrestrial paleoenvironment hypothesis is the presence of iron oxide coatings, inferred to represent the upper horizons of paleosols, along fossiliferous sandstone beds of the Ediacara Member...
November 6, 2017: Geobiology
N Cam, K Benzerara, T Georgelin, M Jaber, J-F Lambert, M Poinsot, F Skouri-Panet, D Moreira, P López-García, E Raimbault, L Cordier, D Jézéquel
Cyanobacteria have long been thought to induce the formation of Ca-carbonates as secondary by-products of their metabolic activity, by shifting the chemical composition of their extracellular environment to conditions favoring mineral precipitation. Some cyanobacterial species forming Ca-carbonates intracellularly were recently discovered. However, the environmental conditions under which this intracellular biomineralization process can occur and the impact of cyanobacterial species forming Ca-carbonates intracellularly on extracellular carbonatogenesis are not known...
October 26, 2017: Geobiology
A L Brady, J Goordial, H J Sun, L G Whyte, G F Slater
Cryptoendolithic lichens and cyanobacteria living in porous sandstone in the high-elevation McMurdo Dry Valleys are purported to be among the slowest growing organisms on Earth with cycles of death and regrowth on the order of 10(3) -10(4)  years. Here, organic biomarker and radiocarbon analysis were used to better constrain ages and carbon sources of cryptoendoliths in University Valley (UV; 1,800 m.a.s.l) and neighboring Farnell Valley (FV; 1,700 m.a.s.l). Δ(14) C was measured for membrane component phospholipid fatty acids (PLFA) and glycolipid fatty acids, as well as for total organic carbon (TOC)...
October 26, 2017: Geobiology
M L Gomes, D A Fike, K D Bergmann, C Jones, A H Knoll
In modern microbial mats, hydrogen sulfide shows pronounced sulfur isotope (δ(34) S) variability over small spatial scales (~50‰ over <4 mm), providing information about microbial sulfur cycling within different ecological niches in the mat. In the geological record, the location of pyrite formation, overprinting from mat accretion, and post-depositional alteration also affect both fine-scale δ(34) S patterns and bulk δ(34) Spyrite values. We report μm-scale δ(34) S patterns in Proterozoic samples with well-preserved microbial mat textures...
October 19, 2017: Geobiology
C H Crosby, J V Bailey
Certain phosphatic grains preserved in the rock record are interpreted as microfossils representing a diversity of microorganisms from bacteria to fossil embryos. In addition to bona fide primary biological features, phosphatic microfossils and fossil embryos commonly exhibit features that result from abiotic precipitation or diagenetic alteration. Distinguishing between abiotic and primary biological features can be difficult, and some features thought to represent biological tissue could instead be artifacts that are unrelated to the original morphology of a preserved organism...
October 19, 2017: Geobiology
L M Ward, A Idei, S Terajima, T Kakegawa, W W Fischer, S E McGlynn
Banded iron formations (BIFs) are rock deposits common in the Archean and Paleoproterozoic (and regionally Neoproterozoic) sedimentary successions. Multiple hypotheses for their deposition exist, principally invoking the precipitation of iron via the metabolic activities of oxygenic, photoferrotrophic, and/or aerobic iron-oxidizing bacteria. Some isolated environments support chemistry and mineralogy analogous to processes involved in BIF deposition, and their study can aid in untangling the factors that lead to iron precipitation...
November 2017: Geobiology
T L Hamilton, P V Welander, H L Albrecht, J M Fulton, I Schaperdoth, L R Bird, R E Summons, K H Freeman, J L Macalady
Little Salt Spring (Sarasota County, FL, USA) is a sinkhole with groundwater vents at ~77 m depth. The entire water column experiences sulfidic (~50 μM) conditions seasonally, resulting in a system poised between oxic and sulfidic conditions. Red pinnacle mats occupy the sediment-water interface in the sunlit upper basin of the sinkhole, and yielded 16S rRNA gene clones affiliated with Cyanobacteria, Chlorobi, and sulfate-reducing clades of Deltaproteobacteria. Nine bacteriochlorophyll e homologues and isorenieratene indicate contributions from Chlorobi, and abundant chlorophyll a and pheophytin a are consistent with the presence of Cyanobacteria...
November 2017: Geobiology
N R Posth, L A Bristow, R P Cox, K S Habicht, F Danza, M Tonolla, N-U Frigaard, D E Canfield
Anoxygenic phototrophic bacteria utilize ancient metabolic pathways to link sulfur and iron metabolism to the reduction of CO2 . In meromictic Lake Cadagno, Switzerland, both purple sulfur (PSB) and green sulfur anoxygenic phototrophic bacteria (GSB) dominate the chemocline community and drive the sulfur cycle. PSB and GSB fix carbon utilizing different enzymatic pathways and these fractionate C-isotopes to different extents. Here, these differences in C-isotope fractionation are used to constrain the relative input of various anoxygenic phototrophs to the bulk community C-isotope signal in the chemocline...
September 3, 2017: Geobiology
V E McCoy, D Asael, N Planavsky
The most notable trend in the sedimentary iron isotope record is a shift at the end of the Archean from highly variable δ(56) Fe values with large negative excursions to less variable δ(56) Fe values with more limited negative values. The mechanistic explanation behind this trend has been extensively debated, with two main competing hypotheses: (i) a shift in marine redox conditions and the transition to quantitative iron oxidation; and (ii) a decrease in the signature of microbial iron reduction in the sedimentary record because of increased bacterial sulfate reduction (BSR)...
September 2017: Geobiology
R Schinteie, J J Brocks
While numerous studies have examined modern hypersaline ecosystems, their equivalents in the geologic past, particularly in the Precambrian, are poorly understood. In this study, biomarkers from ~820 million year (Ma)-old evaporites from the Gillen Formation of the mid-Neoproterozoic Bitter Springs Group, central Australia, are investigated to elucidate the antiquity and paleoecology of halophiles. The sediments were composed of alternating laminae of dolomitized microbial mats and up to 90% anhydrite. Solvent extraction of these samples yielded thermally well-preserved hydrocarbon biomarkers...
September 2017: Geobiology
B Kacar, V Hanson-Smith, Z R Adam, N Boekelheide
Ribulose 1,5-bisphosphate (RuBP) carboxylase/oxygenase (RuBisCO, or Rubisco) catalyzes a key reaction by which inorganic carbon is converted into organic carbon in the metabolism of many aerobic and anaerobic organisms. Across the broader Rubisco protein family, homologs exhibit diverse biochemical characteristics and metabolic functions, but the evolutionary origins of this diversity are unclear. Evidence of the timing of Rubisco family emergence and diversification of its different forms has been obscured by a meager paleontological record of early Earth biota, their subcellular physiology and metabolic components...
September 2017: Geobiology
J Pawłowska, M Łącka, M Kucharska, N Szymańska, K Koziorowska, K Kuliński, M Zajączkowski
The aim of this study was to determine the amount of organic and inorganic carbon in foraminifera specimens and to provide quantitative data on the contribution of foraminifera to the sedimentary carbon pool in Adventfjorden. The investigation was based on three calcareous species that occur commonly in Svalbard fjords: Cassidulina reniforme, Elphidium excavatum and Nonionellina labradorica. Our results show that the species investigated did not contribute substantially to the organic carbon pool in Adventfjorden, because they represented only 0...
September 2017: Geobiology
E Percak-Dennett, S He, B Converse, H Konishi, H Xu, A Corcoran, D Noguera, C Chan, A Bhattacharyya, T Borch, E Boyd, E E Roden
Pyrite (FeS2 ) is the most abundant sulfide mineral on Earth and represents a significant reservoir of reduced iron and sulfur both today and in the geologic past. In modern environments, oxidative transformations of pyrite and other metal sulfides play a key role in terrestrial element partitioning with broad impacts to contaminant mobility and the formation of acid mine drainage systems. Although the role of aerobic micro-organisms in pyrite oxidation under acidic-pH conditions is well known, to date there is very little known about the capacity for aerobic micro-organisms to oxidize pyrite at circumneutral pH...
September 2017: Geobiology
M Kouduka, A S Tanabe, S Yamamoto, K Yanagawa, Y Nakamura, F Akiba, H Tomaru, H Toju, Y Suzuki
Marine sediments contain eukaryotic DNA deposited from overlying water columns. However, a large proportion of deposited eukaryotic DNA is aerobically biodegraded in shallow marine sediments. Cold seep sediments are often anaerobic near the sediment-water interface, so eukaryotic DNA in such sediments is expected to be preserved. We investigated deeply buried marine sediments in the Japan Sea, where a methane hydrate deposit is associated with cold seeps. Quantitative PCR analysis revealed the reproducible recovery of eukaryotic DNA in marine sediments at depths up to 31...
September 2017: Geobiology
M S Bray, J Wu, B C Reed, C B Kretz, K M Belli, R L Simister, C Henny, F J Stewart, T J DiChristina, J A Brandes, D A Fowle, S A Crowe, J B Glass
Reactive Fe(III) minerals can influence methane (CH4 ) emissions by inhibiting microbial methanogenesis or by stimulating anaerobic CH4 oxidation. The balance between Fe(III) reduction, methanogenesis, and CH4 oxidation in ferruginous Archean and Paleoproterozoic oceans would have controlled CH4 fluxes to the atmosphere, thereby regulating the capacity for CH4 to warm the early Earth under the Faint Young Sun. We studied CH4 and Fe cycling in anoxic incubations of ferruginous sediment from the ancient ocean analogue Lake Matano, Indonesia, over three successive transfers (500 days in total)...
September 2017: Geobiology
G Bortoluzzi, T Romeo, V La Cono, G La Spada, F Smedile, V Esposito, G Sabatino, M Di Bella, S Canese, G Scotti, M Bo, L Giuliano, D Jones, P N Golyshin, M M Yakimov, F Andaloro
Ammonium- and Fe(II)-rich fluid flows, known from deep-sea hydrothermal systems, have been extensively studied in the last decades and are considered as sites with high microbial diversity and activity. Their shallow-submarine counterparts, despite their easier accessibility, have so far been under-investigated, and as a consequence, much less is known about microbial communities inhabiting these ecosystems. A field of shallow expulsion of hydrothermal fluids has been discovered at depths of 170-400 meters off the base of the Basiluzzo Islet (Aeolian Volcanic Archipelago, Southern Tyrrhenian Sea)...
September 2017: Geobiology
E E Stüeken, R Buick, R E Anderson, J A Baross, N J Planavsky, T W Lyons
The diversification of macro-organisms over the last 500 million years often coincided with the development of new environmental niches. Microbial diversification over the last 4 billion years likely followed similar patterns. However, linkages between environmental settings and microbial ecology have so far not been described from the ancient rock record. In this study, we investigated carbon, nitrogen, and molybdenum isotopes, and iron speciation in five non-marine stratigraphic units of the Neoarchean Fortescue Group, Western Australia, that are similar in age (2...
August 30, 2017: Geobiology
D A Gold, S S O'Reilly, J Watson, B M Degnan, S M Degnan, J O Krömer, R E Summons
Demosponges are a rich natural source of unusual lipids, some of which are of interest as geochemical biomarkers. Although demosponges are animals, they often host dense communities of microbial symbionts, and it is therefore unclear which lipids can be synthesized by the animal de novo, and which require input from the microbial community. To address this uncertainty, we analyzed the lipids of Amphimdeon queenslandica, the only demosponge with a published genome. We correlated the genetic and lipid repertoires of A...
August 28, 2017: Geobiology
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