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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Transparent soil microcosms for live-cell imaging and non-destructive stable isotope probing of soil microorganisms

Microscale processes are critically important to soil ecology and biogeochemistry yet are difficult to study due to soil’s opacity and complexity. To advance the study of soil processes, we constructed transparent soil microcosms that enable the visualization of microbes via fluorescence microscopy and the non-destructive measurement of microbial activity and carbon uptake in situ via Raman microspectroscopy. We assessed the polymer Nafion and the crystal cryolite as optically transparent soil substrates. We demonstrated that both substrates enable the growth, maintenance, and visualization of microbial cells in three dimensions over time, and are compatible with stable isotope probing using Raman. We applied this system to ascertain that after a dry-down/rewetting cycle, bacteria on and near dead fungal hyphae were more metabolically active than those far from hyphae. These data underscore the impact fungi have facilitating bacterial survival in fluctuating conditions and how these microcosms can yield insights into microscale microbial activities.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2026

Quantitative stable isotope probing (qSIP)-informed metagenomics identifies viruses infecting chemoautotrophs

Aquatic environments absorb ~2.5 gigatonnes of atmospheric carbon each year1, more than the carbon stored in the atmosphere, soils, and all biomass combined. Primary producers transform this dissolved inorganic carbon into biomass that can subsequently flow into other trophic levels, or be released back into the environment through viral lysis. While there is substantial knowledge about the diversity and activity of viruses infecting photoautotrophic primary producers and the ecosystem impact, little is known about viruses infecting chemoautotrophs, representing a gap in our understanding of key processes driving microbial carbon cycling. Here, we combine metagenomics with quantitative 12/13C stable isotopic probing (qSIP) mesocosm experiments in a marine-derived meromictic pond to quantify population-specific isotopic enrichment, identify key chemoautotrophic primary producers, and virus-host dynamics. Isotopically enriched carbon is tracked from the genomes of chemoautotrophs to putative viruses, showing that active populations of hydrogen/sulfur-oxidizing chemoautotrophs (Thiomicrorhabdus, Hydrogenovibrio, Sulfurimonas, Sulfurovum) are targeted by viruses. This work provides the foundation for revealing the diversity and activity of viruses infecting globally-widespread chemoautotrophs. Our study sheds light on trophic interactions that impact microbial carbon cycling in aphotic environments and builds toward biogeochemical models that incorporate viral impacts on chemoautotrophic microbial communities.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS2015

Investigation of Benthic Foraminiferal Non-Traditional Stable Isotopes to Reconstruct Methane Fluxes in Sedimentary Environments

Methane (CH4) is an important greenhouse gas, with a global warming potential much higher than carbon dioxide (CO2) on a short time scale. Even if the residence time of CH4 in the atmosphere is relatively short (tens of years), one of the products of CH4 oxidation is CO2, a greenhouse gas with a much longer residence time in the atmosphere (tens to hundreds of years). CH4 has been proposed as one of the trigger mechanisms for rapid global climate change today and in the geological past. With regards to the geological past, numerous studies proposed the benthic foraminiferal carbon isotope ratio (Delta13C) as a tool to reconstruct the impact of marine CH4 on rapid climate changes; however, the investigation of modern benthic foraminiferal Delta13C have produced inconclusive results. CH4 has a distinctive hydrogen isotope (Delta(D)) and Delta13C signature compared to seawater, and sulfate reduction, often coupled to CH4 anaerobic oxidation in sediments, changes the sulfur isotope signature (Delta34S) of the remaining sulfate in porewater. Therefore, we hypothesize that the Delta(D) and Delta34S signature of infaunal benthic foraminiferal species can provide a complementary approach to Delta13C to study CH4 dynamics in sedimentary environments. Here, we present the preliminary results obtained analyzing Uvigerina peregrina Delta(D) and Delta34S from three different locations at Hydrate Ridge, offshore Oregon. Unfortunately, the lack of chemical data related to the moment of foraminiferal calcification makes difficult to build a robust relationship among the U. peregrina stable isotopes and the CH4 fluxes at the sampling sites. However, our results look very promising, as each site is characterized by a different Delta(D) and Delta34S signature. We emphasize that this study represents the first step in the development of new proxies (Delta(D)) and Delta34S), which may complement the more traditional benthic foraminiferal Delta13C values, to reconstruct marine CH4 fluxes in the geological past.

Borrelli, C.↗
NASA NTRS1988

Characteristics and carbon stable isotopes of fluids in the Southern Kerala granulites and their bearing on the source of CO2

Carbon dioxide-rich inclusions commonly occur in the banded charnockites and khondalites of southern Kerala as well as in the incipient charnockites formed by desiccation of gneisses along oriented zones. The combined high density fluid inclusion isochores and the range of thermometric estimates from mineral assemblages indicate entrapment pressures in the range of 5.4 to 6.1 Kbar. The CO2 equation of state barometry closely compares with the 5 plus or minus 1 Kbar estimate from mineral phases for the region. The isochores for the high density fluid inclusions in all the three rock types pass through the P-T domain recorded by phase equilibria, implying that carbon dioxide was the dominating ambient fluid species during peak metamorphic conditions. In order to constrain the source of fluids and to evaluate the mechanism of desiccation, researchers undertook detailed investigations of the carbon stable isotope composition of entrapped fluids. Researchers report here the results of preliminary studies in some of the classic localities in southern Kerala namely, Ponmudi, Kottavattom, Manali and Kadakamon.

Santosh, M.↗
NASA NTRS1993

Stable isotopes as tracers of methane dynamics in Everglades marshes with and without active populations of methane oxidizing bacteria

The stable carbon isotopic composition of CH4 is used to study the processes that affect it during transport through plants from sediment to the atmosphere. The enhancement of CH4 flux from Cladium and Eleocharis over the flux from open water or clipped sites indicated that these plants served as gas conduits between the sediments and the atmosphere. Lowering of the water table below the sediment surface caused an Everglades sawgrass marsh to shift from emission of CH4 to consumption of atmospheric CH4. Cladium transported gases passively mainly via molecular diffusion and/or effusion instead of actively via bulk flow. Stable isotropic data gave no evidence that CH4 oxidation was occurring in the rhizosphere of Cladium. Both CH4 stable carbon isotope and flux data indicated a lack of CH4 oxidation at the sediment-water interface in Everglades marl soils and its presence in peat soils where 40 to 92 percent of the flux across the sediment-water interface was oxidized.

Happell, James D.↗
DOE OSTI2020

Short-Term Stable Isotope Probing of Proteins Reveals Taxa Incorporating Inorganic Carbon in a Hot Spring Microbial Mat

The upper green layer of the chlorophototrophic microbial mats associated with the alkaline siliceous hot springs of Yellowstone National Park consists of oxygenic cyanobacteria ( Synechococcus spp.), anoxygenic Roseiflexus spp., and several other anoxygenic chlorophototrophs. Synechococcus spp. are believed to be the main fixers of inorganic carbon (C i ), but some evidence indicates that Roseiflexus spp. also contribute to inorganic carbon fixation during low-light, anoxic morning periods. Contributions of other phototrophic taxa have not been investigated. In order to follow the pathway of C i incorporation into different taxa, mat samples were incubated with [ 13 C]bicarbonate for 3 h during the early-morning, low-light anoxic period. Extracted proteins were treated with trypsin and analyzed by mass spectrometry, leading to peptide identifications and peptide isotopic profile signatures containing evidence of 13 C label incorporation. A total of 25,483 peptides, corresponding to 7,221 proteins, were identified from spectral features and associated with mat taxa by comparison to metagenomic assembly sequences. A total of 1,417 peptides, derived from 720 proteins, were detectably labeled with 13 C. Most 13 C-labeled peptides were derived from proteins of Synechococcus spp. and Roseiflexus spp. Chaperones and proteins of carbohydrate metabolism were most abundantly labeled. Proteins associated with photosynthesis, C i fixation, and N 2 fixation were also labeled in Synechococcus spp. Importantly, most proteins of the 3-hydroxypropionate bi-cycle for C i fixation in Roseiflexus spp. were labeled, establishing that members of this taxocene contribute to C i fixation. Other taxa showed much lower [ 13 C]bicarbonate incorporation. IMPORTANCE Yellowstone hot spring mats have been studied as natural models for understanding microbial community ecology and as modern analogs of stromatolites, the earliest community fossils on Earth. Stable-isotope probing of proteins (Pro-SIP) permitted short-term interrogation of the taxa that are involved in the important process of light-driven C i fixation in this highly active community and will be useful in linking other metabolic processes to mat taxa. Here, evidence is presented that Roseiflexus spp., which use the 3-hydroxypropionate bi-cycle, are active in C i fixation. Because this pathway imparts a lower degree of selection of isotopically heavy C i than does the Calvin-Benson-Bassham cycle, the results suggest a mechanism to explain why the natural abundance of 13 C in mat biomass is greater than expected if only the latter pathway were involved. Understanding how mat community members influence the 13 C/ 12 C ratios of mat biomass will help geochemists interpret the 13 C/ 12 C ratios of organic carbon in the fossil record.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS2000

BOREAS TE-5 CO2 Concentration and Stable Isotope Composition

The BOREAS TE-5 team collected measurements in the NSA and SSA on gas exchange, gas composition, and tree growth. This data set contains measurements of the concentration and stable carbon (C-13/C-12 and oxygen (O-18/O-16) isotope ratios of atmospheric CO2 in air samples collected at different heights within forest canopies. The data were collected to determine the influence of photosynthesis and respiration by the forest ecosystems on the concentration and stable isotope ratio of atmospheric CO2 These measurements were collected at the SSA during each 1994 IFC at OJP, OBS, and OA sites. Measurements were also collected at the NSA during each 1994 IFC at the OJP, T6R5S TE UBS, and T2Q6A TE OA sites. The stable isotope ratios are expressed using standard delta notation and in units of per mil. The isotope ratios are expressed relative to the international standard, PDB, for both carbon and oxygen samples. The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Activity Archive Center (DAAC).

Hall, Forrest G.↗
NASA NTRS1998

Stable Isotope Laser Spectrometer for Exploration of Mars

On Earth, measurements of the ratios of stable carbon isotopes have providet much information about geological and biological processes. For example, fractionation of carbon occur in biotic processes and the retention of a distinctive 2-4% contrast in C-13/C-12 between organic carbon and carbonates in rocks as old as 3.8 billion years constitutes some of the firmest evidence for the antiquity of life on the Earth. We have developed a prototype tunable diode laser spectrometer which demonstrates the feasibility of making accurate in situ isotopic ratio measurements on Mars. This miniaturized instrument, with an optical path length of 10 cm should be capable of making accurate C-13/C-12 and N-15/N-14 measurements. Gas samples for measurement are to be produced by pyrolysis using soil samples as small as 50 mg. Measurements of C-13/C-12, O-18/O-16 and N-15/N-14 have been made to a precision of better than 0.1%, and various other isotopes are feasible. This laser technique, which relies on the extremely narrow emission linewidth of tunable diode lasers (less than 0.001/ cm),has favorable features in comparison to mass spectrometry, the standard method of accurate isotopic ratio measurement. The miniature instrument could be ready to deploy c 2003 or other Mars lander missions.

Sauke, Todd B.↗
NASA NTRS1991

Method for determining stable isotope ratios of dissolved organic carbon in interstitial and other natural marine waters

A procedure is described for the analysis of the stable carbon isotopic composition of dissolved organic carbon (DOC) in natural waters from marine and higher-salinity environments. Rapid (less than 5 min) and complete oxidation of DOC is achieved using a modification of previous photochemical oxidation techniques. The CO2 evolved from DOC oxidation can be collected in less than 10 min for isotopic analysis. The procedure is at present suitable for oxidation and collection of 1-5 micromoles of carbon and has an associated blank of 0.1-0.2 micromole of carbon. Complete photochemical oxidation of DOC standards was demonstrated by quantitative recovery of CO2 as measured manometrically. Isotopic analyses of standards by photochemical and high-temperature sealed-tube combustion methods agreed to within 0.3%. Photochemical oxidation of DOC in a representative sediment pore-water sample was also quantitative, as shown by the excellent agreement between the photochemical and sealed-tube methods. The delta 13C values obtained for pore-water DOC using the two methods of oxidation were identical, suggesting that the modified photochemical method is adequate for the isotopically non-fractionated oxidation of pore-water DOC. The procedure was evaluated through an analysis of DOC in pond and pore waters from a hypersaline microbial mat environment. Concentrations of DOC in the water column over the mat displayed a diel pattern, but the isotopic composition of this DOC remained relatively constant (average delta 13C = -12.4%). Pore-water DOC exhibited a distinct concentration maximum in the mat surface layer, and delta 13C of pore-water DOC was nearly 8% lighter at 1.5-2.0-cm depth than in the mat surface layer (0-0.5-cm depth). These results demonstrate the effectiveness of the method in elucidating differences in DOC concentration and delta 13C over biogeochemically relevant spatial and temporal scales. Carbon isotopic analysis of DOC in natural waters, especially pore waters, should be a useful probe of biogeochemical processes in recent environments.

NASA Discipline Exobiology↗
DOE OSTI2024

Land cover and space use influence coyote carnivory: evidence from stable-isotope analysis

For many species, the relationship between space use and diet composition is complex, with individuals adopting varying space use strategies such as territoriality to facilitate resource acquisition. Coyotes ( Canis latrans ) exhibit two disparate types of space use; defending mutually exclusive territories (residents) or moving nomadically across landscapes (transients). Resident coyotes have increased access to familiar food resources, thus improved foraging opportunities to compensate for the energetic costs of defending territories. Conversely, transients do not defend territories and are able to redirect energetic costs of territorial defense towards extensive movements in search of mates and breeding opportunities. These differences in space use attributed to different behavioral strategies likely influence foraging and ultimately diet composition, but these relationships have not been well studied. We investigated diet composition of resident and transient coyotes in the southeastern United States by pairing individual space use patterns with analysis of stable carbon (δ 13 C) and nitrogen (δ 15 N) isotope values to assess diet. During 2016–2017, we monitored 41 coyotes (26 residents, 15 transients) with GPS radio-collars along the Savannah River area in the southeastern United States. We observed a canopy effect on δ 13 C values and little anthropogenic food in coyote diets, suggesting 13 C enrichment is likely more influenced by reduced canopy cover than consumption of human foods. We also observed other land cover effects, such as agricultural cover and road density, on δ 15 N values as well as reduced space used by coyotes, suggesting that cover types and localized, resident-like space use can influence the degree of carnivory in coyotes. Finally, diets and niche space did not differ between resident and transient coyotes despite differences observed in the proportional contribution of potential food sources to their diets. Although our stable isotope mixing models detected differences between the diets of resident and transient coyotes, both relied mostly on mammalian prey (52.8%, SD = 15.9 for residents, 42.0%, SD = 15.6 for transients). Resident coyotes consumed more game birds (21.3%, SD = 11.6 vs 13.7%, SD = 8.8) and less fruit (10.5%, SD = 6.9 vs 21.3%, SD = 10.7) and insects (7.2%, SD = 4.7 vs 14.3%, SD = 8.5) than did transients. Our findings indicate that coyote populations fall on a feeding continuum of omnivory to carnivory in which variability in feeding strategies is influenced by land cover characteristics and space use behaviors.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Stable isotope analysis for assessing the intercrop movement of Microplitis mediator , a larval endoparasitoid of Helicoverpa armigera

Abstract Methods to trace source habitats and movement of parasitic natural enemies in agroecosystems are limited. This study demonstrates that stable carbon isotope analysis offers a valuable new method for revealing the movement of Microplitis mediator (Haliday) (Hymenoptera: Braconidae), a larval endoparasitoid of Helicoverpa armigera Hübner (Lepidoptera: Noctuidae), between C 3 and C 4 plants. Results indicate that M. mediator with δ 13 C values of lower than −22‰ originate from a C 3 plant, whereas those with δ 13 C values of higher than −19‰ develop on a C 4 plant.

Zhang, Qian↗
NASA NTRS1995

Stable isotope analysis at the molecular level: A new approach for determining the origins of amino acids in the Murchison meteorite

A combined gas chromatography/isotope ratio mass spectrometry (GC/IRMS) method has been developed that permits the direct stable carbon isotope analysis of N(O)-trifluoroacetyl-isopropyl esters of individual amino acids and their respective enantiomers at nanomole abundances. Calculation of the original delta C-13 values of the amino acids is accomplished via a correction for the carbon introduced during the derivatization process. Previous GC/IRMS analyses of individual amino acids in the non-hydrolyzed water extract of an interior sample of a Murchison meteorite stone revealed an enrichment in C-13 relative to terrestrial organic matter, in agreement with previous findings for bulk extracts. The range of amino acid delta C-13 values (+5 to +30 per mill, PDB) suggests possible kinetic effects during synthesis. In this study, an apparent kinetic isotope effect was also observed for the amino acid products of a spark discharge experiment. These preliminary resutls are supportive of a similar mechanism for the abiotic synthesis of amino acids in the Murchison meteorite.

Engel, M. H.↗
NASA NTRS2004

LC/MS Method for the Determination of Stable Isotope Labeled Promethazine in Human Plasma

Promethazine (PMZ) is taken by astronauts orally (PO), intramuscularly (IM) or rectally (PR) for space motion sickness. LC/MS method was developed with off-line solid phase extraction to measure plasma concentrations of PMZ given as stable isotope-labeled (SIL) formulations by the three different routes of administration simultaneously. Samples (0.5ml) were loaded on to Waters Oasis HLB co-polymer cartridges and eluted with 1.0 mL methanol. HPLC separation of the eluted sample was performed using an Agilent Zorbax SB-CN column (50 x 2.1 mm) at a flow rate of 0.2 mL/min for 6 min. Acetonitrile/ ammonium acetate (30 mM) in water (3:2, v/v), pH 5.6 plus or minus 0.1, was used as the mobile phase for separation. Concentrations of PMZ, PMZ-d4 and PMZ-d7 and chlorpromazine (internal standard) were determined using a Micromass ZMD single quadrupole mass spectrometer with Electrospray Ionization (ESI). ESI mass spectra were acquired in positive ion mode with selected ion monitoring of [M+ H]dot plus. The method is rapid, reproducible and the assay specific parameters are listed in a table. A novel, sensitive and specific method for the measurement of PMZ and SIL PMZ in human plasma is reported.

Zuwei, Wang↗
NASA NTRS2020

Oxygen and carbon stable isotope composition of the weathering Mg-carbonates on the surface of the LEW 85320 ordinary chondrite: Revisited

New δ13C and δ18O values were measured to constrain the formation mechanisms of two previously identified generations (Antarctica and Houston) of terrestrial weathering carbonates, nesquehonite, which formed on the surface of the Lewis Cliff 85320 ordinary chondrite. These two nesquehonite generations exhibit a characteristic carbon and oxygen isotopic trend which starts with a linear δ13C-δ18O covariation followed by a continuous increase in δ18O with little to no change in δ13C. Based upon the newly developed nesquehonite-water oxygen isotope thermometry and the measured δ18O value of melted ice from Antarctica, the formation temperature of the Antarctic nesquehonite generation was estimated to be -1.9 ± 3℃. Houston nesquehonite generation was most likely formed from an evaporative residue of the melted Antarctic ice at 30 ± 4℃. Modeling the isotopic trend of the two generations suggests that evaporation created large δ18O variations in the nesquehonite while carbon isotopes were stabilized by exchange between the parent liquid and atmospheric CO2. Thus, we suggest that carbonates formed by terrestrial weathering in Antarctica should possess a widespread in δ18O values and a narrow range in δ13C values under dry and cold conditions. Finally, the observed wide spread of δ18O in Martian carbonates (e.g., Allan Hills 84001 and Nakhla) can be explained by evaporation near 0℃ and may have formed by a similar mechanism to that of the nesquehonite in the LEW 85320. Meanwhile, the wide spread of δ13C suggests that two carbon reservoirs with distinct isotope compositions on Mars (e.g., the atmospheric carbon and magmatic carbon) may be actively participating in the formation process.

weathering↗
NASA NTRS1996

Stable isotope analysis of molecular oxygen from silicates and oxides using CO2 laser extraction

A laser-excited system for determination of the oxygen isotope composition of small quantities of silicate and oxide minerals was constructed and tested at JSC. This device is the first reported to use a commercially available helium cryostat to transfer and purify oxygen gas quantitatively within the system. The system uses oxygen gas instead of the conventional CO2 for mass spectrometer analyses. This modification of technique permits determination of all three stable oxygen isotopes, an essential requirement for oxygen isotope analysis of meteoritic material. Tests of the system included analysis of standard silicate materials NBS 28 and UWMG2 garnet, six SNC meteorites, and inclusions and chondrules from the Allende meteorite. Calibration with terrestrial standards was excellent. Meteorite values are close to published values and show no evidence of terrestrial oxygen contamination. The one limitation observed is that, in some runs on fine-grained SNC matrix material, sample results were affected by other samples in the sample holder within the reaction chamber. This reemphasizes the need for special precautions in dealing with fine-grained, reactive samples. Performance of the JSC instrument compares favorably with that of any other instrument currently producing published oxygen isotope data.

Perry, Eugene↗
DOE OSTI2024

Stream water sourcing from high-elevation snowpack inferred from stable isotopes of water: a novel application of d-excess values

About 80 % of the precipitation at the Colorado River's headwaters is snow, and the resulting snowmelt-driven hydrograph is a crucial water source for about 40 million people. Snowmelt from alpine and subalpine snowpack contributes substantially to groundwater recharge and river flow. However, the dynamics of snowmelt progression are not well understood because observations of the high-elevation snowpack are difficult due to challenging access in complex mountainous terrain as well as the cost and labor intensity of currently available methods. We present a novel approach to infer the processes and dynamics of high-elevation snowmelt contributions predicated upon stable hydrogen and oxygen isotope ratios observed in streamflow. We show that deuterium-excess (d-excess) values of stream water could serve as a comparatively cost-effective proxy for a catchment-integrated signal of high-elevation snowmelt contributions to catchment runoff. We sampled stable hydrogen and oxygen isotope ratios of the precipitation, snowpack, and stream water in the East River, a headwater catchment of the Colorado River, and the stream water of larger catchments at sites on the Gunnison River and Colorado River. The d-excess of snowpack increased with elevation; the upper subalpine and alpine snowpack (> 3200 m) had substantially higher d-excess compared to lower elevations (< 3200 m) in the study area. The d-excess values of stream water reflected this because d-excess values increased as the higher-elevation snowpack contributed more to stream water generation later in the snowmelt/runoff season. End-member mixing analyses based on the d-excess data showed that the share of high-elevation snowmelt contributions within the snowmelt hydrograph was on average 44 % and generally increased during melt period progression, up to 70 %. The observed pattern was consistent during 6 years for the East River, and a similar relation was found for the larger catchments on the Gunnison and Colorado rivers. High-elevation snowpack contributions were found to be higher for years with lower snowpack and warmer spring temperatures. Thus, we conclude that the d-excess of stream water is a viable proxy to observe changes in high-elevation snowmelt contributions in catchments at various scales. Inter-catchment comparisons and temporal trends of the d-excess of stream water could therefore serve as a catchment-integrated measure to monitor if mountain systems rely on high-elevation water inputs more during snow drought compared to years of average snowpack depths.

54 ENVIRONMENTAL SCIENCES↗