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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Anaerobic CO2 fixation by the acetogenic bacterium Moorella thermoacetica

Anaerobic bacteria such as Moorella thermoacetica have the capacity of fixing carbon dioxide with carbon monoxide and hydrogen for the production of ethanol, acetic acid, and other useful chemicals. In this study, we evaluated the fixation of CO2 for the production of acetic acid, as a product in its own right but also as precursor for lipid synthesis by oleaginous organisms. We achieved maximum cell optical density of 11.3, acetic acid titer of 31 g/L, and productivity of 0.55 g/L-h at CO mass-transfer rate of 83 mM/h. We also showed electron availability by CO mass transfer limited the process at CO mass transfer rates lower than 30 mM/h. Further enhancement of mass-transfer rate removed such limitations in favor of biological kinetics as main limitation. This work underlines the potential of microbial processes for converting syngas to fuel and chemical products in processes suitable for distributed feedstock utilization. (c) 2013 American Institute of Chemical Engineers AIChE J, 59: 3176-3183, 2013

Hu, P↗
DOE OSTI2012

Efficient CO2 Fixation Pathways: Energy Plant: High Efficiency Photosynthetic Organisms

PETRO Project: UCLA is redesigning the carbon fixation pathways of plants to make them more efficient at capturing the energy in sunlight. Carbon fixation is the key process that plants use to convert carbon dioxide (CO2) from the atmosphere into higher energy molecules (such as sugars) using energy from the sun. UCLA is addressing the inefficiency of the process through an alternative biochemical pathway that uses 50% less energy than the pathway used by all land plants. In addition, instead of producing sugars, UCLA’s designer pathway will produce pyruvate, the precursor of choice for a wide variety of liquid fuels. Theoretically, the new biochemical pathway will allow a plant to capture 200% as much CO2 using the same amount of light. The pathways will first be tested on model photosynthetic organisms and later incorporated into other plants, thus dramatically improving the productivity of both food and fuel crops.

Advanced Fuels↗
DOE OSTI2013

Role of 4-Hydroxybutyrate-CoA Synthetase in the CO2 Fixation Cycle in Thermoacidophilic Archaea

Metallosphaera sedula is an extremely thermoacidophilic archaeon that grows heterotrophically on peptides and chemolithoautotrophically on hydrogen, sulfur, or reduced metals as energy sources. During autotrophic growth, carbon dioxide is incorporated into cellular carbon via the 3-hydroxypropionate/4-hydroxybutyrate cycle (3HP/4HB). To date, all of the steps in the pathway have been connected to enzymes encoded in specific genes, except for the one responsible for ligation of coenzyme A (CoA) to 4HB. Although several candidates for this step have been identified through bioinformatic analysis of the M. sedula genome, none have been shown to catalyze this biotransformation. In this report, transcriptomic analysis of cells grown under strict H-2-CO2 autotrophy was consistent with the involvement of Msed_0406 and Msed_0394. Recombinant versions of these enzymes catalyzed the ligation of CoA to 4HB, with similar affinities for 4HB (K-m values of 1.9 and 1.5 mM for Msed_0406 and Msed_0394, respectively) but with different rates (1.69 and 0.22 mu mol x min(-1) x mg(-1) for Msed_0406 and Msed_0394, respectively). Neither Msed_0406 nor Msed_0394 have close homologs in other Sulfolobales, although low sequence similarity is not unusual for acyl-adenylate-forming enzymes. The capacity of these two enzymes to use 4HB as a substrate may have arisen from simple modifications to acyl-adenylate-forming enzymes. For example, a single amino acid substitution (W424G) in the active site of the acetate/propionate synthetase (Msed_1353), an enzyme that is highly conserved among the Sulfolobales, changed its substrate specificity to include 4HB. The identification of the 4-HB CoA synthetase now completes the set of enzymes comprising the 3HP/4HB cycle.

Hawkins, AS↗
DOE OSTI2024

Novel microbial based enzymatic CO2 fixation mechanisms: Conformational control of enzymatic reactivity

The broad, long-term goal of the research is to provide insight into the mechanism of novel carboxylation and electron bifurcation reactions as paradigms to study how enzyme utilized protein conformational change to protect reactive intermediates and/or control the pathway in a catalytic cycle. catalyzed by enzymes involved in bacterial alkene, ketone, and epoxide metabolism. We are examining two paradigms in which conformational change is a key mechanistic feature of 1) protecting reaction intermediates that are sensitive to breakdown in the presence of water and 2) directing electron flow in reactions that split electron pairs along two pathways in reactions that fine tune metabolic efficiency in microbial metabolism. Both paradigms are of key importance in defining the molecular determinants of reactions relevant to CO 2 capture and fuel upcycling. In the first paradigm the compounds acetone and bicarbonate are activated by the addition of phosphate creating reaction intermediates (phosphoenolacetone and carboxyphosphate) that are very sensitive to breakdown in the presence of water. We are studying the mechanism of how the enzyme protects these reactive intermediates from water by encapsulating them upon their formation within a hydrophobic protein channel leading to an enzyme active site approximately 40 Å away. In the second paradigm, we are examining how the direction of electron transfer reactions can be modulated through protein conformational change that alters either the difference driving force or distance or both between electron transfer pathways in enzymes that catalyze electron bifurcation. We are using a combination of enzyme kinetics, mass spectrometry, spectroscopy, and structural analysis through X-ray diffraction and scattering methods to characterize the mechanism of conformational changes along the catalytic path. Within the context of the mission of the Department of Energy and the core activities of the Energy Biosciences, the results obtained in the study will reveal new insights into the fundamentals of novel carboxylation / CO 2 capture chemical transformations and electron transfer reactions that equate to biological fuel upcycling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Engineering the Cyanobacterial Carbon Concentrating Mechanism for Enhanced CO2 Capture and Fixation

In cyanobacteria CO2 fixation is localized in a special proteinaceous organelle, the carboxysome. The CO2 fixation enzymes are encapsulated by a selectively permeable protein shell. By structurally and functionally characterizing subunits of the carboxysome shell and the encapsulated proteins, we hope to understand what regulates the shape, assembly and permeability of the shell, as well as the targeting mechanism and organization of the encapsulated proteins. This knowledge will be used to enhance CO2 fixation in both cyanobacteria and plants through synthetic biology. The same strategy can also serve as a template for the production of modular synthetic bacterial organelles. Our research is conducted using a variety of techniques such as genomic sequencing and analysis, transcriptional regulation, DNA synthesis, synthetic biology, protein crystallization, Small Angle X-ray Scattering (SAXS), protein-protein interaction assays and phenotypic characterization using various types of cellular imaging, e.g. fluorescence microscopy, Transmission Electron Microscopy (TEM), and Soft X-ray Tomography (SXT).

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Fixation of CO 2 and CO on a diverse range of carbohydrates using anaerobic, non-photosynthetic mixotrophy

Biological CO 2 fixation is an important technology that can assist in combating climate change. Here, we show an approach called anaerobic, non-photosynthetic mixotrophy can result in net CO 2 fixation when using a reduced feedstock. This approach uses microbes called acetogens that are capable of concurrent utilization of both organic and inorganic substrates. In this study, we investigated the substrate utilization of 17 different acetogens, both mesophilic and thermophilic, on a variety of different carbohydrates and gases. Compared to most model acetogen strains, several non-model mesophilic strains displayed greater substrate flexibility, including the ability to utilize disaccharides, glycerol and an oligosaccharide, and growth rates. Three of these non-model strains ( Blautia producta , Clostridium scatologenes and Thermoanaerobacter kivui ) were chosen for further characterization, under a variety of conditions including H 2 - or syngas-fed sugar fermentations and a CO 2 -fed glycerol fermentation. In all cases, CO 2 was fixed and carbon yields approached 100%. Finally, the model acetogen C. ljungdahlii was engineered to utilize glucose, a non-preferred sugar, while maintaining mixotrophic behavior. This work demonstrates the flexibility and robustness of anaerobic, non-photosynthetic mixotrophy as a technology to help reduce CO 2 emissions.

09 BIOMASS FUELS↗
DOE OSTI2014

Carbon dioxide fixation by Metallosphaera yellowstonensis and acidothermophilic iron-oxidizing microbial communities from Yellowstone National Park

The fixation of inorganic carbon (as carbon dioxide) has been documented in all three domains of life and results in the biosynthesis of a diverse suite of organic compounds that support the growth of heterotrophic organisms. The primary aim of this study was to assess the importance of carbon dioxide fixation in high-temperature Fe(III)-oxide mat communities and in pure cultures of one of the dominant Fe(II)-oxidizing organisms (Metallosphaera yellowstonensis strain MK1) present in situ. Protein-encoding genes of the complete 3-hydroxypropionate/4-hydroxybutyrate (3-HP/4-HB) carbon fixation pathway were identified in pure-cultures of M. yellowstonensis strain MK1. Metagenome sequencing from the same environments also revealed genes for the 3-HP/4-HB pathway belonging to M. yellowstonensis populations, as well as genes for a complete reductive TCA cycle from Hydrogenobaculum spp. (Aquificales). Stable isotope (13CO2) labeling was used to measure the fixation of CO2 by M. yellowstonensis strain MK1, and in ex situ assays containing live Fe(III)-oxide microbial mats. Results showed that M. yellowstonensis strain MK1 fixes CO2 via the 3-HP/4-HB pathway with a fractionation factor of ~ 2.5 ‰. Direct analysis of the 13C composition of dissolved inorganic C (DIC), dissolved organic C (DOC), landscape C and microbial mat C showed that mat C is comprised of both DIC and non-DIC sources. The estimated contribution of DIC carbon to biomass C (> ~ 35%) is reasonably consistent with the relative abundance of known chemolithoautotrophs and corresponding CO2 fixation pathways detected in metagenome sequence. The significance of DIC as a major source of carbon for Fe-oxide mat communities provides a foundation for examining microbial interactions in these systems that are dependent on the activity of autotrophic organisms such as Hydrogenobaculum and Metallosphaera spp.

Sulfolobales, Crenarchaeota, stable isotope analys↗
DOE OSTI2024

Alternative electron pathways of photosynthesis power green algal CO2 capture

Abstract Microalgae contribute to about half of global net photosynthesis, which converts sunlight into the chemical energy (ATP and NADPH) used to transform CO2 into biomass. Alternative electron pathways of photosynthesis have been proposed to generate additional ATP that is required to sustain CO2 fixation. However, the relative importance of each alternative pathway remains elusive. Here, we dissect and quantify the contribution of cyclic, pseudo-cyclic, and chloroplast-to-mitochondrion electron flows for their ability to sustain net photosynthesis in the microalga Chlamydomonas reinhardtii. We show that (i) each alternative pathway can provide sufficient additional energy to sustain high CO2 fixation rates, (ii) the alternative pathways exhibit cross-compensation, and (iii) the activity of at least one of the three alternative pathways is necessary to sustain photosynthesis. We further show that all pathways have very different efficiencies at energizing CO2 fixation, with the chloroplast–mitochondrion interaction being the most efficient. Overall, our data lay bioenergetic foundations for biotechnological strategies to improve CO2 capture and fixation.

Biochemistry & Molecular Biology↗
DOE OSTI2024

Bioprocess and microbe engineering for total carbon utilization in biofuel production

Some aspects of this invention provide methods and bioreactors for converting a carbon source into a lipid. In some embodiments, lipid production is carried out in an aerobic fermentor and carbon dioxide generated during lipid production is converted into a carbon substrate by CO2 fixation in an anaerobic fermentor. In some embodiments, the carbon substrate generated by CO2 fixation is used as the carbon source for lipid production, thus achieving total carbon utilization in lipid production.

Stephanopoulos, Gregory↗
DOE OSTI2012

Acclimation of the Global Transcriptome of the Cyanobacterium Synechococcus sp. Strain PCC 7002 to Nutrient Limitations and Different Nitrogen Sources

The unicellular, euryhaline cyanobacterium Synechococcus sp. strain PCC 7002 is a model organism for laboratory-based studies of cyanobacterial metabolism and is a potential platform for biotechnological applications. Two of its most notable properties are its exceptional tolerance of high-light intensity and very rapid growth under optimal conditions. In this study, transcription profiling by RNAseq has been used to perform an integrated study of global changes in transcript levels in cells subjected to limitation for the major nutrients CO2, nitrogen, sulfate, phosphate, and iron. Transcriptional patterns for cells grown on nitrate, ammonia, and urea were also studied. Nutrient limitation caused strong decreases of transcript levels of the genes encoding major metabolic pathways, especially for components of the photosynthetic apparatus, CO2 fixation, and protein biosynthesis. Uptake mechanisms for the respective nutrients were strongly up-regulated. The transcription data further suggest that major changes in the composition of the NADH dehydrogenase complex occur upon nutrient limitation. Transcripts for flavoproteins increased strongly when CO2 was limiting. Genes involved in protection from oxidative stress generally showed high, constitutive transcript levels, which possibly explains the high-light tolerance of this organism. The transcriptomes of cells grown with ammonia or urea as nitrogen source showed increased transcript levels for components of the CO2 fixation machinery compared to cells grown with nitrate, but in general transcription differences in cells grown on different N-sources exhibited surprisingly minor differences.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2013

Comparative genomics of freshwater Fe-oxidizing bacteria: implications for physiology, ecology, and systematics

The two microaerophilic, Fe-oxidizing bacteria (FeOB) Sideroxydans ES-1 and Gallionella ES-2 have single circular chromosomes of 3.00 and 3.16 Mb that encode 3049 and 3006 genes, respectively. Multi-locus sequence analysis (MLSA) confirmed the relationship of these two organisms to one another, and indicated they may form a novel order, the Gallionellalaes, within the Betaproteobacteria. Both are adapted for chemolithoautotropy, including pathways for CO2-fixation, and electron transport pathways adapted for growth at low O2-levels, an important adaptation for growing on Fe(II). Both genomes contain Mto-genes implicated in iron-oxidation, as well as other genes that could be involved in Fe-oxidation. Nearly 10% of their genomes are devoted to environmental sensing, signal transduction, and chemotaxis, consistent with their requirement for growing in narrow redox gradients of Fe(II) and O2. There are important differences as well. Sideroxydans ES-1 is more metabolically flexible, and can utilize reduced S-compounds, including thiosulfate, for lithotrophic growth. It has a suite of genes for nitrogen fixation. Gallionella ES-2 contains additional gene clusters for exopolysaccharide production, and has more capacity to resist heavy metals. Both strains contain genes for hemerythrins and globins, but ES-1 has an especially high numbers of these genes that may be involved in oxygen homeostasis, or storage. The two strains share homology with the marine FeOB Mariprofundus ferrooxydans PV-1 in CO2 fixation genes, and respiratory genes. In addition, ES-1 shares a suite of 20 potentially redox active genes with PV-1, as well as a large prophage. Combined these genetic, morphological, and physiological differences indicate that these are two novel species, Sideroxydans lithotrophicus ES-1T (ATCC 700298T; JCM 14762; DSMZ 22444; NCMA B100), and Gallionella capsiferriformans ES-2T (ATCC 700299T; JCM 14763; DSMZ 22445; NCMA B101).

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2012

Fermentation, Hydrogen, and Sulfur Metabolism in Multiple Uncultivated Bacterial Phyla

BD1-5, OP11, and OD1 bacteria have been widely detected in anaerobic environments, but their metabolisms remain unclear owing to lack of cultivated representatives and minimal genomic sampling. We uncovered metabolic characteristics for members of these phyla, and a new lineage, PER, via cultivation-independent recovery of 49 partial to near-complete genomes from an acetate-amended aquifer. All organisms were nonrespiring anaerobes predicted to ferment. Three augment fermentation with archaeal-like type II and III ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO) that couples adenosine monophosphate salvage with CO2 fixation, a pathway previously not described in Bacteria. Members of OD1 reduce sulfur and may pump protons using archaeal-type hydrogenases. For six organisms, the UGA stop codon is translated as tryptophan. All bacteria studied here may play previously unrecognized roles in hydrogen production, sulfur cycling, and fermentation of refractory sedimentary carbon.

bacterial phyla↗
DOE OSTI2023

Restricting electron flow at cytochrome b6f when downstream electron acceptors are severely limited

Abstract Photosynthetic organisms frequently experience abiotic stress that restricts their growth and development. Under such circumstances, most absorbed solar energy cannot be used for CO2 fixation and can cause the photoproduction of reactive oxygen species (ROS) that can damage the photosynthetic reaction centers of PSI and PSII, resulting in a decline in primary productivity. This work describes a biological “switch” in the green alga Chlamydomonas reinhardtii that reversibly restricts photosynthetic electron transport (PET) at the cytochrome b6f (Cyt b6f) complex when the capacity for accepting electrons downstream of PSI is severely limited. We specifically show this restriction in STARCHLESS6 (sta6) mutant cells, which cannot synthesize starch when they are limited for nitrogen (growth inhibition) and subjected to a dark-to-light transition. This restriction represents a form of photosynthetic control that causes diminished electron flow to PSI and thereby prevents PSI photodamage but does not appear to rely on a ΔpH. Furthermore, when electron flow is restricted, the plastid alternative oxidase (PTOX) becomes active, functioning as an electron valve that dissipates some excitation energy absorbed by PSII and allows the formation of a proton motive force (PMF) that would drive some ATP production (potentially sustaining PSII repair and nonphotochemical quenching [NPQ]). The restriction at the Cyt b6f complex can be gradually relieved with continued illumination. This study provides insights into how PET responds to a marked reduction in availability of downstream electron acceptors and the protective mechanisms involved.

Plant Sciences↗
DOE OSTI2026

Data for A Role for Differential Rubisco Activase Isoform Expression in C4 Bioenergy Grasses at High Temperature

Rubisco activase (Rca) facilitates the release of sugar-phosphate inhibitors at Rubisco catalytic sites during CO2 fixation. Most plant species express two Rca isoforms, the larger Rca-α and the shorter Rca-β, either by alternative splicing from a single gene or expression from separate genes. The mechanism of Rubisco activation by Rca isoforms has been intensively studied in C3 plants. However, the functional role of Rca in C4 plants where Rubisco and Rca are located in a much higher [CO2] compartment is less clear. In this study, we selected four C4 bioenergy grasses and the model C4 grass setaria ( Setaria viridis ) to investigate the role of Rca in C4 photosynthesis. All five C4 grass species contained two Rca genes, one encoding Rca-α and the other Rca-β, which were positioned closely together in the genomes. A variety of abiotic stress-related motifs were identified in the Rca-α promoter of each grass, and while the Rca-β gene was constantly highly expressed at ambient temperature, Rca-α isoforms were expressed only at high temperature but never surpassed 30% of Rca-β content. The pattern of Rca-α induction on transition to high temperature and reduction on return to ambient temperature was the same in all five C4 grasses. In sorghum ( Sorghum bicolor ), sugarcane ( Saccharum officinarum ), and setaria, the induction rate of Rca-α was similar to the recovery rate of photosynthesis and Rubisco activation at high temperature. This association between Rca-α isoform expression and maintenance of Rubisco activation at high temperature suggests that Rca-α has a functional thermo-protective role in carbon fixation in C4 grasses by sustaining Rubisco activation at high temperature.

Genomics↗
DOE OSTI2013

Visible-Light Photoredox Catalysis: Selective Reduction of Carbon Dioxide to Carbon Monoxide by a Nickel N-Heterocyclic Carbene-Isoquinoline Complex

The solar-driven reduction of carbon dioxide to value-added chemical fuels is a longstanding challenge in the fields of catalysis, energy science, and green chemistry. In order to develop effective CO2 fixation, several key considerations must be balanced, including (1) catalyst selectivity for promoting CO2 reduction over competing hydrogen generation from proton reduction, (2) visible-light harvesting that matches the solar spectrum, and (3) the use of cheap and earth-abundant catalytic components. In this report, we present the synthesis and characterization of a new family of earth-abundant nickel complexes supported by N-heterocyclic carbene amine ligands that exhibit high selectivity and activity for the electrocatalytic and photocatalytic conversion of CO2 to CO. Systematic changes in the carbene and amine donors of the ligand have been surveyed, and [Ni(Prbimiq1)]2+ (1c, where Prbimiq1 = bis(3-(imidazolyl)isoquinolinyl)propane) emerges as a catalyst for electrochemical reduction of CO2 with the lowest cathodic onset potential (Ecat = 1.2 V vs SCE). Using this earth-abundant catalyst with Ir(ppy)3 (where ppy = 2-phenylpyridine) and an electron donor, we have developed a visible-light photoredox system for the catalytic conversion of CO2 to CO that proceeds with high selectivity and activity and achieves turnover numbers and turnover frequencies reaching 98,000 and 3.9 s1, respectively. Further studies reveal that the overall efficiency of this solar-to-fuel cycle may be limited by the formation of the active Ni catalyst and/or the chemical reduction of CO2 to CO at the reduced nickel center and provide a starting point for improved photoredox systems for sustainable carbon-neutral energy conversion.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗