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Results for “CO2 fixation”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Rubisco kinetic acclimation at the holoenzyme level

Kinetic acclimation enables proteins to adjust their activity in response to environmental perturbations. For the CO 2 -fixing enzyme Rubisco, kinetic acclimation may be conferred by its small subunits. Plants express multiple small subunits and vary their expression with temperature. Here, we demonstrate that different small subunits can bind to the same Rubisco to form a heterogeneous holoenzyme. These small subunits had distinct kinetic effects which aligned with changes in holoenzyme structure and stability. Our findings indicate that small subunits enable Rubisco kinetic acclimation via manipulation of flexibility. By assembling a more rigid active site in higher temperatures and a more flexible one in lower temperatures, plants maximize the efficiency of their Rubisco, and thus photosynthesis, over a wide range of temperatures.

CO2 fixation↗
DOE OSTI2024

Homologous acetone carboxylases select Fe(II) or Mn(II) as the catalytic cofactor

The Irving-Williams series refers to the predicted stabilities of transition metal complexes where the observed general stability for divalent first-row transition metal complexes increase across the row. Acetone carboxylases (ACs) use a coordinated divalent metal at their active site in the catalytic conversion of bicarbonate and acetone to form acetoacetate. Highly homologous ACs discriminate among different divalent metals at their active sites such that variations of the enzyme prefer Mn(II) over Fe(II), defying Irving-Williams-predicted behavior. Defining the determinants that promote metal discrimination within the first-row transition metals is of broad fundamental importance in understanding metal-mediated catalysis and metal catalyst design.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Acetyl-CoA Synthesis Through a Bicyclic Carbon-Fixing Pathway in Gas-Fermenting Bacteria

Gas-fermenting acetogens can upgrade one-carbon (C1) compounds (such as CO2 and CO) to the two-carbon (C2) metabolite acetyl coenzyme A (CoA) and convert sugar feedstocks to acetyl-CoA with minimal CO2 emissions. Fulfilling the biosynthetic potential of these microbes requires overcoming challenges in pathway engineering. Here we design a synthetic acetyl-CoA bi-cycle-in addition to the natural carbon-fixing pathways-for C2 metabolite synthesis. This pathway produces an acetyl-CoA by fixation of two CO2 equivalents via three functional modules acting in sequence: carbon fixation, gluconeogenesis and non-oxidative glycolysis. The pathway was examined by in silico thermodynamic and kinetic analyses. The prototypic pathway was implemented in a syngas-fermenting organism, Clostridium ljungdahlii DSM 13528, by expressing a heterologous phosphoketolase that can work with other native enzymes in the host acetogen. The carbon conversion pathway is possible under various growth conditions and is independent of the Wood-Ljungdahl pathway for the valorization of H2 and CO2. This study reports the improvement of carbon conversion using a reductive acetyl-CoA bi-cycle and the potential impact of redox homoeostasis in the acetogenic host for industrial applications of gas fermentation.

Acetyl-CoA↗
DOE OSTI2019

High yield algal biomass production without concentrated CO2 supply under open pond conditions

Methods and systems for efficient culturing of algae in open ponds. Further, the methods include a method for culturing algae in an open pond medium that is free of any concentrated supply of CO2, and no concentrated source of CO2 is used to supply carbon for culturing the algae. Also, the algae are cultured in the open pond which has a pH above 9.5. In addition, the open pond medium has incorporated therein an inorganic carbon buffer at a specified concentration under conditions for obtaining an increased biomass. Also, the pH above 9.5 permits sufficient increased fixation of atmospheric CO2 into the open pond medium.

Pendyala, Brahmaiah↗
NASA NTRS1993

Microscale characterization of dissolved organic matter production and uptake in marine microbial mat communities

Intertidal marine microbial mats exhibited biologically mediated uptake of low molecular weight dissolved organic matter (DOM), including D-glucose, acetate, and an L-amino acid mixture at trace concentrations. Uptake of all compounds occurred in darkness, but was frequently enhanced under natural illumination. The photosystem 2 inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU) generally failed to inhibit light-stimulated DOM uptake. Occasionally, light plus DCMU-amended treatments led to uptake rates higher than light-incubated samples, possibly due to phototrophic bacteria present in subsurface anoxic layers. Uptake was similar with either 3H- or 14C-labeled substrates, indicating that recycling of labeled CO2 via photosynthetic fixation was not interfering with measurements of light-stimulated DOM uptake. Microautoradiographs showed a variety of pigmented and nonpigmented bacteria and, to a lesser extent, cyanobacteria and eucaryotic microalgae involved in light-mediated DOM uptake. Light-stimulated DOM uptake was often observed in bacteria associated with sheaths and mucilage surrounding filamentous cyanobacteria, revealing a close association of organisms taking up DOM with photoautotrophic members of the mat community. The capacity for dark- and light-mediated heterotrophy, coupled to efficient retention of fixed carbon in the mat community, may help optimize net production and accretion of mats, even in oligotrophic waters.

NASA Discipline Exobiology↗
DOE OSTI2024

Reducing stomatal density by expression of a synthetic epidermal patterning factor increases leaf intrinsic water use efficiency and reduces plant water use in a C4 crop

Abstract Enhancing crop water use efficiency (WUE) is a key target trait for climatic resilience and expanding cultivation on marginal lands. Engineering lower stomatal density to reduce stomatal conductance (gs) has improved WUE in multiple C3 crop species. However, reducing gs in C3 species often reduces photosynthetic carbon gain. A different response is expected in C4 plants because they possess specialized anatomy and biochemistry which concentrates CO2 at the site of fixation. This modifies the relationship of photosynthesis (AN) with intracellular CO2 concentration (ci), such that photosynthesis is CO2 saturated and reductions in gs are unlikely to limit AN. To test this hypothesis, genetic strategies were investigated to reduce stomatal density in the C4 crop sorghum. Constitutive expression of a synthetic epidermal patterning factor (EPF) transgenic allele in sorghum led to reduced stomatal densities, reduced gs, reduced plant water use, and avoidance of stress during a period of water deprivation. In addition, moderate reduction in stomatal density did not increase stomatal limitation to AN. However, these positive outcomes were associated with negative pleiotropic effects on reproductive development and photosynthetic capacity. Avoiding pleiotropy by targeting expression of the transgene to specific tissues could provide a pathway to improved agronomic outcomes.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1994

Elevated CO2: Impact on diurnal patterns of photosynthesis in natural microbial ecosystems

Algae, including blue-green algae (cyanobacteria), are the major source of fixed carbon in many aquatic ecosystems. Previous work has shown that photosynthetic carbon fixation is often enhanced in the presence of additional carbon dioxide (CO2). This study was undertaken to determine if this CO2 fertilization effect extended to microbial mats, and, if so, at what times during the day might the addition of CO2 affect carbon fixation. Four microbial mats from diverse environments were selected, including mats from a hypersaline pond (area 5, Exportadora de Sal, Mexico), the marine intertidal (Lyngbya, Laguna Ojo de Liebre, Mexico), an acidic hotspring (Cyanidium, Nymph Creek, Yellowstone National Park), and an acidic stream at ambient temperature (Zygogonium, Yellowstone National Park). Carbon fixation in the absence of additional CO2 essentially followed the rising and falling sunlight levels, except that during the middle of the day there was a short dip in carbon fixation rates. The addition of CO2 profoundly enhanced carbon fixation rates during the daylight hours, including during the midday dip. Therefore, it is unlikely that the midday dip was due to photoinhibition. Surprisingly, enhancement of carbon fixation was often greatest in the early morning or late afternoon, times when carbon fixation would be most likely to be light limited.

Rothschild, L. J.↗
DOE OSTI2020

Chapter 8. Hybrid Biological–Inorganic Systems for CO 2 Conversion to Fuels

The biological reduction of CO 2 into organic carbon is integral to the formation and maintenance of all life on earth. An urgent need to mitigate the effects of CO 2 on our atmosphere has provided an imperative to exploit biological CO 2 fixation for the conversion of CO2 into valuable and energy rich fuels. Photosynthesis uses only sunlight, water, and CO2 as starting materials to form all biomass.

CO2 Conversion to Fuels↗
DOE OSTI2021

Effect of tectonic processes on biosphere–geosphere feedbacks across a convergent margin

The subsurface is among Earth’s largest biomes, but the extent to which microbial communities vary across tectonic plate boundaries or interact with subduction-scale geological processes remains unknown. Here we compare bacterial community composition with deep-subsurface geochemistry from 21 hot springs across the Costa Rican convergent margin. We find that cation and anion compositions of the springs reflect the dip angle and position of the underlying tectonic structure and also correlate with the bacterial community. Co-occurring microbial cliques related to cultured chemolithoautotrophs that use the reverse tricarboxylic acid cycle (rTCA) as well as abundances of metagenomic rTCA genes correlate with concentrations of slab-volatilized carbon. This, combined with carbon isotope evidence, suggests that fixation of slab-derived CO2 into biomass may support a chemolithoautotrophy-based subsurface ecosystem. We calculate that this forearc subsurface biosphere could sequester 1.4 × 10 9 to 1.4 × 10 10 mol of carbon per year, which would decrease estimates of the total carbon delivered to the mantle by 2 to 22%. Furthermore, based on the observed correlations, we suggest that distribution and composition of the subsurface bacterial community are probably affected by deep tectonic processes across the Costa Rican convergent margin and that, by sequestering carbon volatilized during subduction, these chemolithoautotrophic communities could in turn impact the geosphere.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1979

Laboratory simulations of the pyrolytic release experiments - An interim report

During its operation on Mars the pyrolytic release experiment (PR) detected the fixation of small amounts of CO2 and/or CO. Laboratory simulations of the experimental conditions were made in an attempt to substantiate the previous conclusion that these reactions were chemical rather than biological. After pretreatment and incubation under various conditions, pyrolytic analysis was used to indicate the extent of surface catalyzed conversion of (C-14)O2 or (C-14)O to (C-14)-organic compounds. This abiotic synthesis was detected in experiments with three iron oxides, viz. hematite, magnetite and maghemite. When the incubation atmosphere was supplemented with water vapor, the levels of synthesis were in a range comparable to that detected in the Viking PR tests. An abiotic synthesis was also detected in experiments with a mixture of clays and minerals (Mars analog soil) or with montmorillonite artificially enriched in iron. With either substratum the reaction appeared to be the result of a photocatalytic synthesis of (C-14)-organics from (C-14)O and surface hydroxyl groups. This process was not dependent on the presence of water vapor in the incubation atmosphere. Although a duplication of the Viking data has not been achieved, these findings support the abiotic interpretation of the PR results.

Hubbard, J. S.↗
NASA NTRS1990

Model of carbon fixation in microbial mats from 3,500 Myr ago to the present

Using modern microbial mats as analogs for ancient stromatolites, it is shown that the rate of carbon fixation is higher at the greater levels of atmospheric CO2 that were probably present in the past. It is suggested that carbon fixation in microbial mats was not carbon-limited during the early Precambrian, but became carbon-limited as the supply of inorganic carbon decreased. Carbon limitation led to a lower rate of carbon fixation, especially towards the end of the Precambrian.

Rothschild, Lynn J.↗
DOE OSTI2026

Leafweb: Leaf Gas Exchange and Pulse-Amplitude Modulated Fluorometry for C4 Species, June 2026 Release

This dataset contains leaf gas exchange and Pulse-Amplitude Modulated (PAM) fluorometry for 98 C4 species. The C4 photosynthetic pathway employs specialized CO2 concentration mechanisms and Kranz anatomy to enrich CO2 concentration around Rubisco, the enzyme that catalyzes carbon fixation in the Calvin-Benson cycle to suppress photorespiration and increase the use efficiencies of light, nitrogen, and water as compared to the C3 photosynthetic pathways. Large-scale C4 photosynthetic datasets are relatively scarce, which has affected C4 photosynthesis research. To improve C4 photosynthetic data availability, Leafweb organized an effort to systematically collect, compile, standardize, and organize measurements of leaf gas exchange and/or Pulse-Amplitude Modulated (PAM) fluorometry of C4 species. This derived a C4 photosynthetic dataset containing measurements made by independent researchers in multiple countries in various environments (field, garden, or greenhouse). It covers three biochemical subtypes – the nicotinamide adenine dinucleotide phosphate-malic enzyme (NADP-ME), nicotinamide adenine dinucleotide-malic enzyme (NAD-ME), and phosphoenolpyruvate carboxykinase (PEP-CK) subtypes. This dataset is useful for using Artificial Intelligence / Machine Learning and mechanistic models to study C4 photosynthesis and compare across different biochemical subtypes. This dataset contains 3 compressed (*.zip) folders containing 1,892 data files in comma-separate values (*.csv) format. Additional metadata are provided: one data dictionary and a file-level metadata file in comma-separate values (*.csv) format and a user guide in PDF (*.pdf) format.

Zhou, Haoran [Tianjin University, China]↗
NASA NTRS1996

Interacting effects of photoperiod and photosynthetic photon flux on net carbon assimilation and starch accumulation in potato leaves

The effect of photoperiod (PP) on net carbon assimilation rate (Anet) and starch accumulation in newly mature canopy leaves of 'Norland' potato (Solanum tuberosum L.) was determined under high (412 varies as mol m-2s-1) and low (263 varies as mol m-2s-1) photosynthetic photon flux (PPF) conditions. The Anet decreased from 13.9 to 11.6 and 9.3 micromoles m-2s-1, and leaf starch increased from 70 to 129 and 118 mg g-1 drymass (DM) as photoperiod (PP) was increased from 12/12 to 18/6, and 24/0, respectively. Longer PP had a greater effect with high PPF conditions than with low PPF treatments, with high PPF showing greater decline in Anet. Photoperiod did not affect either the CO2 compensation point (50 micromoles mol-1) or CO2 saturation point (1100-1200 micromoles mol-1) for Anet. These results show an apparent limit to the amount of starch that can be stored (approximately 15% DM) in potato leaves. An apparent feedback mechanism exists for regulating Anet under high PPF, high CO2, and long PP, but there was no correlation between Anet and starch concentration in individual leaves. This suggests that maximum Anet cannot be sustained with elevated CO2 conditions under long PP (> or = 12 hours) and high PPF conditions. If a physiological limit exists for the fixation and transport of carbon,then increasing photoperiod and light intensity under high CO2 conditions is not the most appropriate means to maximize the yield of potatoes.

NASA Discipline Number 61-20↗
DOE OSTI2024

Electrocatalytic nitrate reduction: controlling adsorbate affinity to tailor reaction products

Every year, Haber-Bosch nitrogen fixation to form ammonia releases immense volumes of CO2. At the same time, nitrate contamination from untreated wastewater threatens human health across the US. Development of circular processes to efficiently upgrade waste nitrate for reuse is critical to sustainably address this growing environmental hazard. Electrochemical reduction of nitrate operates at ambient temperatures and pressures, and can leverage distributed renewable energy sources and water as a hydrogen source for ammonia production. However, current catalysts lack electron efficiency in reducing nitrate versus water, lack selectivity in forming ammonia as a product, or rely on expensive rare metals, making widespread implementation unfeasible. To overcome these limitations, this proposal seeks a mechanistic understanding of nitrate electrochemical reduction on earth abundant metals and their alloys, with the goal of identifying active-site properties that improve both Faradaic efficiency and product selectivity. This insight will extend to other electrocatalytic reductive process that compete with water reduction.

30 DIRECT ENERGY CONVERSION↗
NASA NTRS2012

State of Climate 2011 - Global Ocean Phytoplankton

Phytoplankton photosynthesis in the sun lit upper layer of the global ocean is the overwhelmingly dominant source of organic matter that fuels marine ecosystems. Phytoplankton contribute roughly half of the global (land and ocean) net primary production (NPP; gross photosynthesis minus plant respiration) and phytoplankton carbon fixation is the primary conduit through which atmospheric CO2 concentrations interact with the ocean s carbon cycle. Phytoplankton productivity depends on the availability of sunlight, macronutrients (e.g., nitrogen, phosphorous), and micronutrients (e.g., iron), and thus is sensitive to climate-driven changes in the delivery of these resources to the euphotic zone

Siegel, D. A.↗
NASA NTRS1981

Rates of fixation by lightning of carbon and nitrogen in possible primitive atmospheres

A thermochemical-hydrodynamic model of the production of trace species by electrical discharges has been used to estimate the rates of fixation of C and N by lightning in the primitive atmosphere. Calculations for various possible mixtures of CH4, CO2, CO, N2, H2, and H2O reveal that the prime species produced were probably HCN and NO and that the key parameter determining the rates of fixation was the ratio of C atoms to O atoms in the atmosphere. Atmospheres with C more abundant than O have large HCN fixation rates, in excess of 10 to the 17th molecules/J, but small NO yields. However, when O is more abundant than C, the NO fixation rate approaches 10 to the 17th molecules/J while the HCN yield is small. The implications for the evolution of life are discussed.

Chameides, W. L.↗
NASA NTRS1997

Interannual Variability in Soil Trace Gas (CO2, N2O, NO) Fluxes and Analysis of Controllers

Interannual variability in flux rates of biogenic trace gases must be quantified in order to understand the differences between short-term trends and actual long-term change in biosphere-atmosphere interactions. We simulated interannual patterns (1983-1988) of global trace gas fluxes from soils using the NASA Ames model version of CASA (Carnegie-Ames-Stanford Approach) in a transient simulation mode. This ecosystem model has been recalibrated for simulations driven by satellite vegetation index data from the NOAA Advanced Very High Resolution Radiometer (AVHRR) over the mid-1980s. The predicted interannual pattern of soil heterotropic CO2 emissions indicates that relatively large increases in global carbon flux from soils occurred about three years following the strong El Nino Southern Oscillation (ENSO) event of 1983. Results for the years 1986 and 1987 showed an annual increment of +1 Pg (1015 g) C-CO2 emitted from soils, which tended to dampen the estimated global increase in net ecosystem production with about a two year lag period relative to plant carbon fixation. Zonal discrimination of model results implies that 80-90 percent of the yearly positive increments in soil CO2 emission during 1986-87 were attributable to soil organic matter decomposition in the low-latitudes (between 30 N and 30 S). Soils of the northern middle-latitude zone (between 30 N and 60 N) accounted for the residual of these annual increments. Total annual emissions of nitrogen trace gases (N2O and NO) from soils were estimated to vary from 2-4 percent over the time period modeled, a level of variability which is consistent with predicted interannual fluctuations in global soil CO2 fluxes. Interannual variability of precipitation in tropical and subtropical zones (30 N to 20 S appeared to drive the dynamic inverse relationship between higher annual emissions of NO versus emissions of N2O. Global mean emission rates from natural (heterotrophic) soil sources over the period modeled (1983-1988) were estimated at 57.1 Pg C-CO2yr-1, 9.8Tg (1012 g) N-NO yr-1, and 9.7 Tg N-N2O yr-1. Chemical fertilizer contributions to global soil N gas fluxes were estimated at between 1.3 to 7.3 Tg N-NO yr-1, and 1.2 to 4.0 Tg N-N2O yr-1.

Potter, C.↗