Roger Summons

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Papers by Roger Summons

Carbon Oxidation State in Microbial Polar Lipids Suggests Adaptation to Hot Spring Temperature and Redox Gradients

Frontiers in Microbiology, Feb 20, 2020

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Oxygen-18 incorporation into malic acid during nocturnal carbon dioxide fixation in crassulacean acid metabolism plants. A new approach to estimating in vivo carbonic anhydrase activity

Journal of Biological Chemistry, 1984

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Lipid Biomarker Record of the Serpentinite-Hosted Ecosystem of the Samail Ophiolite, Oman and Implications for the Search for Biosignatures on Mars

Astrobiology, 2020

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Alcohols of microbial mats from Lake 2A on Kiritimati Island

In Supplement to: Bühring, Solveig I; Smittenberg, Rienk H; Sachse, Dirk; Lipp, Julius S; Golubic, S; Sachs, Julian P; Hinrichs, Kai-Uwe; Summons, Roger E (2009): A hypersaline microbial mat from the Pacific Atoll Kiritimati: Insight into composition and carbon fixation using biomarker analyses a..., Jun 16, 2010

Organic Geochemical Signatures of Early Life on Earth

Treatise on Geochemistry, 2014

Organic geochemical data concerned with recognizing biological activity on the early Earth are re... more Organic geochemical data concerned with recognizing biological activity on the early Earth are reviewed. We discuss the stable carbon isotopic records of organic and inorganic carbon, the nature of preserved organic matter as well as microscopic, macroscopic, and molecular fossils that record the presence of microbes in the world's oldest sediments.

Chirality of meteoritic free and IOM-derived monocarboxylic acids and implications for prebiotic organic synthesis

Geochimica et Cosmochimica Acta, 2014

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Vagrant oils: geochemical signposts to unrecognised petroleum systems

... tropical: break-up of Comi Sea Focene lacustrine oil shales oil shale resource yet to be deve... more

Environmental conditions and microbial community structure during the Great Ordovician Biodiversification Event; a multi-disciplinary study from the Canning Basin, Western Australia

Global and Planetary Change, Dec 1, 2017

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Abstract: Spectroscopic and Microscopic Characterization of Carbonaceous Material in Archaean Cherts, Pilbara Craton, Western Australia

Spatially Resolved, In Situ Carbon Isotope Analysis of Archean Organic Matter

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Carbon and sulfur isotopic signatures of ancient life and environment at the microbial scale: Neoarchean shales and carbonates

Geobiology, Oct 24, 2015

An approach to coordinated, spatially resolved, in situ carbon isotope analysis of organic matter... more An approach to coordinated, spatially resolved, in situ carbon isotope analysis of organic matter and carbonate minerals, and sulfur three-and four-isotope analysis of pyrite with an unprecedented combination of spatial resolution, precision, and accuracy is described. Organic matter and pyrite from eleven rock samples of Neoarchean drill core express nearly the entire range of d 13 C, d 34 S, D 33 S, and D 36 S known from the geologic record, commonly in correlation with morphology, mineralogy, and elemental composition. A new analytical approach (including a set of organic calibration standards) to account for a strong correlation between H/C and instrumental bias in SIMS d 13 C measurement of organic matter is identified. Small (2-3 lm) organic domains in carbonate matrices are analyzed with sub-permil accuracy and precision. Separate 20-to 50-lm domains of kerogen in a single~0.5 cm 3 sample of the~2.7 Ga Tumbiana Formation have d 13 C = À52.3 AE 0.1& and À34.4 AE 0.1&, likely preserving distinct signatures of methanotrophy and photoautotrophy. Pyrobitumen in the~2.6 Ga Jeerinah Formation and the~2.5 Ga Mount McRae Shale is systematically 13 C-enriched relative to co-occurring kerogen, and associations with uraniferous mineral grains suggest radiolytic alteration. A large range in sulfur isotopic compositions (including higher D 33 S and more extreme spatial gradients in D 33 S and D 36 S than any previously reported) are observed in correlation with morphology and associated mineralogy. Changing systematics of d 34 S, D 33 S, and D 36 S, previously investigated at the millimeter to centimeter scale using bulk analysis, are shown to occur at the micrometer scale of individual pyrite grains. These results support the emerging view that the dampened signature of mass-independent sulfur isotope fractionation (S-MIF) associated with the Mesoarchean continued into the early Neoarchean, and that the connections between methane and sulfur metabolism affected the production and preservation of S-MIF during the first half of the planet's history.

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In Situ Carbon and Sulfur Isotope Analysis of Archean Organic Matter and Pyrite

Stable isotopic compositions of biologically important elements (e.g., C and S) in sedimentary ro... more Stable isotopic compositions of biologically important elements (e.g., C and S) in sedimentary rocks are valuable biosignatures to the extent that they indicate the presence and variable expression of microbial metabolisms in space and time. Strong interactions between the carbon and sulfur cycles (e.g., via organic matter remineralization during microbial sulfate reduction) make coordinated, in situ C and S isotope analysis by secondary ion mass spectrometry (SIMS) a particularly powerful tool. In rocks ranging in age from 2.7-2.5 Ga, expansions in the ranges of delta C-13 of organic matter and delta S-34 of pyrite likely reflect the increasing influence of oxygenic photosynthesis in the surface ocean (as well as methane and sulfur metabolisms in deeper waters), whereas the large range of mass independent sulfur isotope fractionation (Delta S-33) suggests that the atmosphere remained anoxic until approx 2.4 Gyr ago. We report in situ delta C-13 measurements of organic matter in the approx 2.7-2.6 Ga Carawine Dolomite, Marra Mamba Iron Formation, and Jeerinah, Wittenoom, and Tumbiana Formations, as well as the approx 2.5 Ga Mount McRae Shale. We also report in situ delta S-24 and Delta S-33 measurements of pyrite associated with organic matter in a subset of these samples. In a single square cm sample of the Tumbiana Formation with bulk delta C-13(sub org) of -49.7% (VPDB), two distinct kerogen types have delta C-13 values, measured in situ, consistent with oxygenic photosynthesis (-33%) and methane metabolism (-52%). In a sample from the ABDP-9 core, radiobitumen associated with a uraniferous mineral grain is C-13-enriched by 8% (-26.8%0) relative to average in situ kerogen (-34.9%0) and similar in delta C-13 to solvent extractable hydrocarbons from the Mount McRae Shale (avg delta C-13 = -27.1 %). Average reproducibility for delta C-13 was 0.4% (2 SD) using a 6 micron spot and 0.8% using a 3 micron spot. In situ sulfur isotope analyses of 33 authigenic pyrite grains in 3 samples of the ABDP-9 core using a 10 micron spot (2 SD reproducibility = 0.4% for delta S-34 and -0.1% for Delta S-33) show a range of 28.1 % in delta S-34 (-10.3 to 17.8%) and 13.3%0 in Delta S-33 (-3.8 to 9.5%), whereas the range from 132 bulk analyses across 84 m of core is 19.4% for delta S-34 and 11.5% for Delta S-33. Coordinated, in situ carbon and sulfur isotope analyses in one ABDP-9 sample are shown. In situ values from this kerogen-pyrite association are within 0.1% of the bulk value in the case of delta C-13 and higher by several permil in the case of delta S-34 and Delta S-33. Coordinated in situ carbon and sulfur isotope analyses in rocks deposited during key intervals of environmental change (e.g., the Great Oxidation Event) can refine our understanding of the mode and tempo of change. In Earth's oldest sedimentary rocks, and in extraterrestrial samples, these coordinated in situ analyses may reveal biosignatures in the form of isotopic correlations at the scale of individual microorganisms and their microhabitats

Redox-Controlled Ammonium Storage and Overturn in Ediacaran Oceans

Frontiers in Earth Science, 2021

As a key nutrient, nitrogen can limit primary productivity and carbon cycle dynamics, but also ev... more As a key nutrient, nitrogen can limit primary productivity and carbon cycle dynamics, but also evolutionary progress. Given strong redox-dependency of its molecular speciation, environmental conditions can control nitrogen localization and bioavailability. This particularly applies to periods in Earth history with strong and frequent redox fluctuations, such as the Neoproterozoic. We here report on chlorophyll-derived porphyrins and maleimides in Ediacaran sediments from Oman. Exceptionally light δ15N values (< –10‰) in maleimides derived from anoxygenic phototrophs point towards ammonium assimilation at the chemocline, whereas the isotopic offset between kerogens and chlorophyll-derivatives indicates a variable regime of cyanobacterial and eukaryotic primary production in surface waters. Biomarker and maleimide mass balance considerations imply shallow euxinia during the terminal Ediacaran and a stronger contribution of anoxygenic phototrophs to primary productivity, possibly as...

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Microbially influenced formation of Neoarchean ooids

Geobiology, 2018

Ooids are accretionary grains commonly reported from turbulent, shallow‐water environments. They ... more 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. Recently described carbonate ooids from the 2.9 Ga Pongola Supergroup, South Africa, include well‐preserved examples composed of diagenetic dolomite interpreted to have formed from a high‐Mg‐calcite precursor. Spatial distributions of organic matter and elements associated with metabolic activity (N, S, and P) were interpreted as evidence for ...

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Biostratigraphy and Paleobiogeography of the Proterozoic

The Proterozoic Biosphere

Hydrocarbons of microbial mats from Lake 2A on Kiritimati Island

Fatty acids of microbial mats from Lake 2A on Kiritimati Island

Fatty acids, alcohols and hydrocarbons of microbial mats from Lake 2A on Kiritimati Island

Modern microbial mats are widely recognized as useful analogs for the study of biogeochemical pro... more Modern microbial mats are widely recognized as useful analogs for the study of biogeochemical processes relevant to paleoenvironmental reconstruction in the Precambrian. We combined microscopic observations and investigations of biomarker composition to investigate community structure and function in the upper layers of a thick phototrophic microbial mat system from a hypersaline lake on Kiritimati (Christmas Island) in the Northern Line Islands, Republic of Kiribati. In particular, an exploratory incubation experiment with 13C-labeled bicarbonate was conducted to pinpoint biomarkers from organisms actively fixing carbon. A high relative abundance of the cyanobacterial taxa Aphanocapsa and Aphanothece was revealed by microscopic observation, and cyanobacterial fatty acids and hydrocarbons showed 13C-uptake in the labeling experiment. Microscopic observations also revealed purple sulfur bacteria (PSB) in the deeper layers. A cyclic C19:0 fatty acid and farnesol were attributed to this group that was also actively fixing carbon. Background isotopic values indicate Calvin-Benson cycle-based autotrophy for cycC19:0 and farnesol-producing PSBs. Biomarkers from sulfate-reducing bacteria (SRB) in the top layer of the mat and their 13C-uptake patterns indicated a close coupling between SRBs and cyanobacteria. Archaeol, possibly from methanogens, was detected in all layers and was especially abundant near the surface where it contained substantial amounts of 13C-label. Intact glycosidic tetraether lipids detected in the deepest layer indicated other archaea. Large amounts of ornithine and betaine bearing intact polar lipids could be an indicator of a phosphate-limited ecosystem, where organisms that are able to substitute these for phospholipids may have a competitive advantage.

Low fossilization potential of keratin protein revealed by experimental taphonomy

Palaeontology, 2017

Recent studies have suggested the presence of keratin in Cenozoic-to Mesozoicaged fossils. Howeve... more Recent studies have suggested the presence of keratin in Cenozoic-to Mesozoicaged fossils. However, ultrastructural studies revealing exposed melanosomes in many fossil keratinous tissues suggest that keratin should rarely, if ever, be preserved. In this study, keratin's stability through diagenesis was tested using microbial decay and maturation experiments on various keratinous structures. The residues were analyzed by pyrolysis-gas chromatographymass spectrometry and compared to unpublished feather and hair fossils and published fresh and fossil melanin from squid ink. Results show that highly matured feathers (200-250 °C/250 bars/24 hours) become a volatile-rich, thick fluid with semi-distinct pyrolysis compounds from those observed in less degraded keratins (i.e., fresh, decayed, moderately matured, and decayed and moderately matured), suggesting hydrolysis of peptide bonds and potential degradation of free amino acids. Neither melanization nor keratin (secondary) structure (e.g., ⍺vs. β-keratin) produced different pyrograms-melanin pyrolysates are largely a subset of those from proteins and proteins have characteristic pyrolysates. Analyses of fossil fur and feather lacked amides, succinimide, and piperazines (present even in highly matured keratin) and showed pyrolysis compounds more similar to fossil and fresh melanin than to non-matured or matured keratin. Although the highly matured fluid was not water soluble at room temperature, it readily dissolved at elevated temperatures easily attained during diagenesis, meaning it can leach away from the fossil. Future interpretations of fossils must consider that calcium phosphate and pigments are the only components of keratinous structures known to survive fossilisation in mature sediments.

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Lipidomics of the sea sponge Amphimedon queenslandica and implication for biomarker geochemistry

Geobiology, 2017

Demosponges are a rich natural source of unusual lipids, some of which are of interest as geochem... more 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. queenslandica to identify which biomarkers could potentially be synthesized and/or modified by the sponge. The fatty acid profile of A. queenslandica is dominated by an unusual Δ 5,9 fatty acid (cis-5,9-hexacosadienoic acid)similar to what has been found in other members of the Amphimdeon genus-while the sterol profile is dominated by C 27-C 29 derivatives of cholesterol. Based on our analysis of the A. queenslandica genome, we predict that this sponge can synthesize sterols de novo, but it lacks critical genes necessary to synthesize basic saturated and unsaturated fatty acids. However, it does appear to have the genes necessary to modify simpler products into a more complex "algal-like" assemblage of unsaturated fatty acids. Ultimately, our results provide additional support for the poriferan affinity of 24-isopropylcholestanes in Neoproterozoic-age rocks (the "sponge biomarker" hypothesis) and suggest that some algal proxies in the geochemical record could also have animal contributions.

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Carbon Oxidation State in Microbial Polar Lipids Suggests Adaptation to Hot Spring Temperature and Redox Gradients

Frontiers in Microbiology, Feb 20, 2020

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Oxygen-18 incorporation into malic acid during nocturnal carbon dioxide fixation in crassulacean acid metabolism plants. A new approach to estimating in vivo carbonic anhydrase activity

Journal of Biological Chemistry, 1984

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Lipid Biomarker Record of the Serpentinite-Hosted Ecosystem of the Samail Ophiolite, Oman and Implications for the Search for Biosignatures on Mars

Astrobiology, 2020

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Alcohols of microbial mats from Lake 2A on Kiritimati Island