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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

CO Oxidation on Au/TiO 2 : Condition-Dependent Active Sites and Mechanistic Pathways

We present results of ab initio electronic structure and molecular dynamics simulations (AIMD), as well as microkinetic modeling of CO oxidation catalyzed by TiO2 supported Au nanocatalysts. A coverage-dependent microkinetic analysis, based on energetics obtained with density functional methods, shows that the dominant kinetic pathway, activated oxygen species, and catalytic active sites are all strongly depended on both temperature and oxygen partial pressure. A dynamic single atom catalytic (DSAC) mechanism for CO oxidation is proposed to be the dominant (but not the exclusive) pathway for this reaction under oxidative conditions below T < 400 K. This mechanism proceeds via an Au+-CO species that transfers from the Au-cluster to a surface oxygen ad-atom, where it reacts with the TiO2 support with a Mars van Krevelen mechanism to form CO2 and subsequently reintegrates back into the gold cluster to complete the catalytic cycle. At 300 = T = 600 K oxygen-bound single Au+CO sites and the perimeter sites of the Au-nanoparticle work in tandem to optimally catalyze the reaction. Above 600 K a variety of alternate pathways associated with the perimeter sites of the Au nanoparticle and/or the single atom site are found to be the most active pathways. Overall our results highlight the importance of the dynamic behavior of interfacial area between the catalysts and the support, which allows for a high degree of adaptation. This work was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences and performed at the Pacific Northwest National Laboratory (PNNL). PNNL is a multi-program national laboratory operated for Department of Energy by Battelle. Computational resources were provided at W. R. Wiley Environmental Molecular Science Laboratory (EMSL), a national scientific user facility sponsored by the Department of Energy’s Office of Biological and Environmental Research located at PNNL and the National Energy Research Scientific Computing Center (NERSC) at Lawrence Berkeley National Laboratory.

Wang, Yang-Gang↗
DOE OSTI2013

3013 DE Inner Container Closure Weld Corrosion Evaluation

Destructive evaluation (DE) of 3013 containers is one part of the U. S. Department of Energy Integrated Surveillance Program. During standard DE of 3013 containers, visual examinations for pitting and stress corrosion cracking (SCC) are performed on the accessible surfaces of the outer, inner, and convenience containers, which make up the 3013 container. As a result of 3013 DE additional analysis, the area near the inner container closure weld has been identified as being a region of increased corrosion susceptibility, which may provide a pathway for corrosive gases to the outer container. This area has a higher residual stress, an altered microstructure, and less corrosion resistant weld oxides as a result of the welding process as well as a lower temperature than other areas of the container, which may increase the absorption of moisture on the surface. The deposition of moisture in this stressed region could lead to pitting and stress corrosion cracking. During FY2013, the inner container closure weld area was more closely evaluated on several archived samples from DE containers. These containers included FY09 DE2, FY12 DE4, FY12 DE6 and FY12 DE7 and the Hanford High Moisture Container. The additional examinations included visual observations with a stereomicroscope, scanning electron microscopy along with energy dispersive spectroscopy for chemical analysis, and serial metallography of the sidewall and lid that are part of the inner container closure weld region. Pitting was observed in all the samples taken from the closure weld regions of the examined inner containers. This pitting was generally less 20 µm with most less than 5µm. These pits were similar in depth to those observed in the vapor exposed surfaces of teardrops in the shelf life corrosion testing. Cracking was not observed on either the vapor-exposed surfaces of the teardrop coupons or the inner container closure weld region. Further testing is necessary to determine if the conditions in the welded inner container could support SCC during the 50 year life time for the 3013 container.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Risk-Informed MultiPphysics BestEestimate Plus Uncertainties (BEPU) Application Development of RELAP5-3D Perturbation Model

The United States nuclear industry is facing a strong challenge to ensure maximum safety while enhancing economic benefit. Safety is a key parameter to all aspects related to light water reactor (LWR) nuclear power plants (NPPs), especially cost savings. Since the goal is to extend the lifetimes of these NPPs, the traditional deterministic safety concept may not guarantee a current economic asset. The Light Water Reactor Sustainability (LWRS) Program has been promoting a wide range of research and development (R&D) in this field to maximize the safety, economics, and performance of these NPPs through improved scientific understanding. One of the best practices to achieve this goal is to identify and optimize safety margins, which can lead to cost reduction. To do this, under the LWRS framework, the Risk-Informed Systems Analysis (RISA) Pathway will focus on the optimization of safety margin and minimization of uncertainties to ensure both safety and economics at the highest level. The RISA Pathway will provide enhanced capabilities for analyzing and characterizing LWR systems performance by developing and demonstrating methods, tools, and data to enable risk-informed margins management (RIMM). The goals of the RISA Pathway are twofold: (1) deploy the risk-informed tools and methods that enable better representation of safety margins and factors that contribute to cost and safety; and (2) conduct advanced risk assessment applications with industry to support margin management strategies that enable more cost-effective plant operation. The tools and methods provided by the RISA Pathway will support effective margin management for both active and passive safety systems, structures, and components (SSC) of an NPP. The tools and methods used in the RISA Pathway should have high confidence and highest technical maturity for and implementation to industry at its current setting. They should also have a capability to support risk-informed decision making for both probabilistic and deterministic elements of safety. The RISA Pathway will, therefore, perform a comprehensive assessment of verification and validation (V&V) status of RISA Toolkit to enhance credibility RISA Toolkit which be used by industry. This report summarizes RELAP5-3D development activities for best estimated and uncertainty (BEPU) capability to support ongoing RISA Pathway pilot projects for risk informed uncertainty quantification applications. Work scope includes (1) development of initial perturbation model for selected closure laws and (2) testing of suitable probability distribution functions (PDF) for the selected correlations. Developed BEPU modules are tested with selected separate effect cases and compared with conventional thermal-hydraulics model.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2026

Design Status and Experimental Strategy for Initial Molten Salt Irradiation Experiments in HFIR

The development and deployment of molten salt reactor (MSR) technologies require experimental capabilities that can evaluate molten fuel salt behavior and structural material performance under representative irradiation conditions. Although modeling and separate effects testing provide important insight, there remains a critical lack of in-pile data that capture the coupled effects of neutron irradiation, temperature, salt chemistry, and time. Informed by lessons learned from historical MSR programs and recent international irradiation efforts, this report presents a structured approach to addressing existing gaps in molten salt irradiation testing using the High Flux Isotope Reactor (HFIR). A phased irradiation strategy is presented that incrementally increases experimental complexity while managing cost, risk, and facility constraints. The framework progresses from passive, nonfueled static capsule experiments to fueled, instrumented, and ultimately circulating molten salt systems, providing a pathway for materials screening, mechanistic understanding, and qualification-relevant testing. The report defines a near-term Phase 1 passive capsule concept, associated irradiation conditions, and a conceptual post-irradiation examination strategy. Ongoing modeling, out-of-pile testing, and safety analysis activities are described to support continued capability maturation and to enable future phases of molten salt irradiation testing in support of MSR technology deployment.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2017

Degradation of Adenine on the Martian Surface in the Presence of Perchlorates and Ionizing Radiation: A Reflectron Time-of-flight Mass Spectrometric Study

The aim of the present work is to unravel the radiolytic decomposition of adenine (C{sub 5}H{sub 5}N{sub 5}) under conditions relevant to the Martian surface. Being the fundamental building block of (deoxy)ribonucleic acids, the possibility of survival of this biomolecule on the Martian surface is of primary importance to the astrobiology community. Here, neat adenine and adenine–magnesium perchlorate mixtures were prepared and irradiated with energetic electrons that simulate the secondary electrons originating from the interaction of the galactic cosmic rays with the Martian surface. Perchlorates were added to the samples since they are abundant—and therefore relevant oxidizers on the surface of Mars—and they have been previously shown to facilitate the radiolysis of organics such as glycine. The degradation of the samples were monitored in situ via Fourier transformation infrared spectroscopy and the electron ionization quadruple mass spectrometric method; temperature-programmed desorption profiles were then collected by means of the state-of-the-art single photon photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS), allowing for the detection of the species subliming from the sample. The results showed that perchlorates do increase the destruction rate of adenine by opening alternative reaction channels, including the concurrent radiolysis/oxidation of the sample. This new pathway provides a plethora of different radiolysis products that were identified for the first time. These are carbon dioxide (CO{sub 2}), isocyanic acid (HNCO), isocyanate (OCN{sup −}), carbon monoxide (CO), and nitrogen monoxide (NO); an oxidation product containing carbonyl groups (R{sub 1}R{sub 2}–C=O) with a constrained five-membered cyclic structure could also be observed. Cyanamide (H{sub 2}N–C≡N) was detected in both irradiated samples as well.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Plasma-Catalyst Reactivity Control of Surface Nitrogen Species through Plasma-Temperature-Programmed Hydrogenation to Ammonia

Nonthermal plasma activation of N 2 can facilitate nitrogen adsorption on metal catalysts at low bulk temperatures and atmospheric pressure. Here, we apply a plasma-assisted temperature-programmed reaction (plasma-TPRxn) for ammonia (NH 3 ) synthesis using sequential exposure of a silica-supported metal catalyst to N 2 plasma followed by thermal hydrogen treatment while ramping the temperature to decouple the plasma activation of N 2 from surface catalyzed hydrogenation steps. This approach eliminates the effects from bulk plasma phase reactions, thereby allowing for direct interrogation of plasma activated nitrogen on the active metal surfaces. We confirm previously reported spectroscopic observations that show plasma-generated surface nitrogen can be converted to NH 3 through surface catalyzed pathways. Further, we demonstrate that the ammonia desorption peak temperature is sensitive to metal, with Pt desorbing NH 3 at the lowest temperature. Unsteady state microkinetic models of desorption kinetics as a function of initial N coverage and metal recover observed trends in NH 3 desorption temperatures and confirm that observed results reflect hydrogenation of plasma-induced N accommodation at each surface. In total, we show that the hydrogenation ability of the catalyst after plasma activation of N 2 is responsible for the reactivity trends observed in plasma-assisted NH 3 synthesis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Exploring the Quantum Universe: Pathways to Innovation and Discovery in Particle Physics

Now more than ever, particle physics is an international, even global, endeavor. The experiments needed to address the most profound questions of our field often require resources and cooperation at a global scale and can take more than a decade to design and build. We found the scope of our charge and the responsibility it represents humbling. Throughout our deliberations, we were aware that the impact of our recommendations would be felt past the end of the next decade and beyond the borders of the US particle physics program. The recommended program reflects the consensus of the panel.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

In Situ Fabrication of PtCo Alloy Embedded in Nitrogen-Doped Graphene Nanopores as Synergistic Catalyst for Oxygen Reduction Reaction

A novel PtCo alloy in situ etched and embedded in graphene nanopores (PtCo/NPG) as a high-performance catalyst for ORR was reported. Graphene nanopores were fabricated in situ while forming PtCo nanoparticles that were uniformly embedded in the graphene nanopores. Given the synergistic effect between PtCo alloy and nanopores, PtCo/NPG exhibited 11.5 times higher mass activity than that of the commercial Pt/C cathode electrocatalyst. DFT calculations indicated that the nanopores in NPG cannot only stabilize PtCo nanoparticles but can also definitely change the electronic structures, thereby change its adsorption abilities. This enhancement can lead to a favorable reaction pathway on PtCo/NPG for ORR. This study showed that PtCo/NPG is a potential candidate for the next generation of Pt-based catalysts in fuel cells. This study also offered a promising alternative strategy and enabled the fabrication of various kinds of metal/graphene nanopore nanohybrids with potential applications in catalysts and potential use for other technological devices. The authors acknowledge the financial support from the National Basic Research Program (973 program, No. 2013CB733501), Zhejiang Provincial Education Department Research Program (Y201326554) and the National Natural Science Foundation of China (No. 21306169, 21101137, 21136001, 21176221 and 91334013). D. Mei acknowledges the support from the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle. Computing time was granted by the grand challenge of computational catalysis of the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL) and by the National Energy Research Scientific Computing Center (NERSC).

electrocatalysis↗
DOE OSTI2019

CoBAMP: a Python framework for metabolic pathway analysis in constraint-based models

Abstract Summary CoBAMP is a modular framework for the enumeration of pathway analysis concepts, such as elementary flux modes (EFM) and minimal cut sets in genome-scale constraint-based models (CBMs) of metabolism. It currently includes the K-shortest EFM algorithm and facilitates integration with other frameworks involving reading, manipulation and analysis of CBMs. Availability and implementation The software is implemented in Python 3, supported on most operating systems and requires a mixed-integer linear programming optimizer supported by the optlang framework. Source-code is available at https://github.com/BioSystemsUM/cobamp.

Vieira, Vítor (ORCID:0000000196049586)↗
DOE OSTI2022

Electrochemically-Induced Phase Transformations in Battery Storage Compounds (Final Technical Report)

Compounds of interest for ion storage in advanced batteries frequently exhibit phase transformations as the working ion concentration varies. Under large electrochemical driving forces inherent to practical use, systems are often driven far from equilibrium. This program combines experiments and theory to understand the phase transition behavior of ion insertion compounds when electrochemically driven far from equilibrium. As model systems, we focus on alkaline metal phosphates AMPO4 (A = alkali; M = first row transition metal) of olivine structure, which are both technologically interesting and ideally suited for fundamental study due to the ability to systematically tune transformation strain, and along with it, the phase transformation pathway. Behavior in compositions having large transformation strains (~15 vol%) requiring plasticity for strain accommodation is emphasized. Experimental techniques include operando characterization of structure while simultaneously varying electrokinetic parameters, and high resolution microscopy of nanoscale and interfacial phenomena. Phase-field modeling is used to model the thermodynamics and kinetics of competing transformation pathways, extended to include the effects of plasticity, and integrated with porous electrode kinetic theory to treat multi-particle effects. Success in this project will lead to an ability to design ion storage compounds with predictable transformation pathways, electrochemical kinetics, capacity utilization, and durability. New technologically important compounds may also be discovered.

36 MATERIALS SCIENCE↗
DOE OSTI2017

A REVIEW OF HUMAN-SYSTEM INTERFACE DESIGN ISSUES OBSERVED DURING ANALOG-TO-DIGITAL AND DIGITAL-TO-DIGITAL MIGRATIONS IN U.S. NUCLEAR POWER PLANTS

The United States (U.S.) Department of Energy (DOE) Light Water Reactor Sustainability (LWRS) program is developing a scientific basis through targeted research and development (R&D) to support the U.S. nuclear power plant (NPP) fleet in extending their existing licensing period and ensuring their long-term reliability, productivity, safety, and security. Over the last several years, human factors engineering (HFE) professionals at the Idaho National Laboratory (INL) have supported the LWRS Advanced Instrumentation, Information, and Control (II&C) System Technologies pathway across several U.S. commercial NPPs in analog-to-digital migrations (i.e., turbine control systems) and digital-to-digital migrations (i.e., Safety Parameter Display System). These efforts have included in-depth human factors evaluation of proposed human-system interface (HSI) design concepts against established U.S. Nuclear Regulatory Commission (NRC) design guidelines from NUREG-0700, Rev 2 to inform subsequent HSI design prior to transitioning into Verification and Validation. This paper discusses some of the overarching design issues observed from these past HFE evaluations. In addition, this work presents some observed challenges such as common tradeoffs utilities are likely to face when introducing new HSI technologies into NPP hybrid control rooms. The primary purpose of this work is to distill these observed design issues into general HSI design guidance that industry can use in early stages of HSI design.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2019

LWRS Newsletter March 2019 Issue 28

The latest issue of the LWRS Program Newsletter (Issue 28) was recently posted on the LWRS Program website. This issue includes the following articles: • Stakeholder Engagement Review Meeting • Simulating the Effects of Neutron Irradiation on Concrete with the MOSAIC Software • Risk and Cost Analysis of Utilizing FLEX Equipment for Efficient Maintenance in Nuclear Power Plants • Integration of Classical PRA models into Dynamic PRA • Toward a Predictive Model for Cabling Failure: An interdisciplinary, collaborative effort between the University of Minnesota–Duluth and the Materials Research Pathway • Compact Digital Modernization – Enabling Nuclear Power Plant Operations and Maintenance Cost Benefits • Increasing the Value of the U.S. Nuclear Reactor Fleet

42 ENGINEERING↗
DOE OSTI2021

Mechanistic studies of NH 3 -assisted reduction of mononuclear Cu(ii) cation sites in Cu-CHA zeolites

Cu-Exchanged zeolites catalyze various redox reactions including the selective catalytic reduction (SCR) of NO x with NH 3 and the partial oxidation of hydrocarbons. The reduction of Cu(II) cations to Cu(I) by NH 3 alone has been observed experimentally, yet fundamental details regarding the Cu active site requirements, reaction stoichiometry, and reaction mechanism remain incompletely understood. Here, we synthesized model Cu-exchanged chabazite (Cu-CHA) zeolites with varying Cu ion densities and distributions of mononuclear Cu(II) ion site types (Cu 2+ , (CuOH) + ) and studied NH 3 -assisted Cu(II) reduction reactions using a combination of spectroscopic, titrimetric, and gas-phase product analysis methods. In situ UV-visible and X-ray absorption spectroscopies were used to monitor and quantify the transient reduction of Cu(II) to Cu(I) during exposure to NH 3 (473 K), in concert with titration methods that use NO and NH 3 co-reductants to fully reduce to the Cu(I) state any residual Cu(II) ions that remained after treatments in NH 3 alone for a given time period. The techniques provide quantitative evidence that both mononuclear Cu(II) site types are able to reduce in NH 3 alone, and do so to similar extents as a function of time. NH 3 temperature programmed reduction (TPR) revealed that the reaction stoichiometry of NH 3 -assisted reduction forms approximately one equivalent of N 2 per 6 Cu sites, regardless of Cu speciation or density, consistent with a six-electron reduction process whereby two NH 3 molecules react with six Cu(II) species to produce one N 2 molecule and six Cu(I) species. Furthermore, these findings provide new insights into the reaction pathways and mechanisms by which NH 3 alone reduces mononuclear Cu(II) sites in zeolites, which are undesired side-reactions that occur during steady-state NO x SCR and can unintentionally influence SCR-relevant spectroscopic or titrimetric characterization experiments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

FORCE Regression Testing

Via programs including the Light Water Reactor Sustainability and Integrated Energy Systems, the U.S. Department of Energy has invested in the Framework for Optimization of ResourCes and Economics (FORCE) software framework (Idaho National Laboratory 2024a) for the technical and economic analysis of nuclear-integrated energy systems (IES). Nuclear IES expand the use of nuclear from traditional baseload electricity generation to a flexible and adaptive source of combined heat and power. Nuclear heat can be used in the production of a variety of energy currencies such as hydrogen and ammonia as well as other heat applications including water desalination and district heating. FORCE is designed with the intent to provide interconnected analysis tools that enable the accurate technical and economic assessment of specific nuclear IES configurations for individual energy markets. FORCE consists of three main analysis pathways: HYBRID (Idaho National Laboratory 2024b), which contains high-resolution physical models for IES; Holistic Energy Resource Optimization Network (HERON) (Idaho National Laboratory 2024c), which analyzes IES long-term economic viability; and Optimization of Real-time Capacity Allocation (ORCA) (Idaho National Laboratory 2024d), designed for real-time control of IES via digital twins and optimal decision making, including autonomous and remote operation research. Development of the FORCE ecosystem is guided by three pillars: capability, which assures that the computational requirements of IES analysis are met by the software tools; reliability, which provides for consistent code performance and expected behaviors; and accessibility, which lowers the barrier to entry for using the software and accelerates analysis by users beyond the FORCE primary developers. Reliability of the FORCE ecosystem is established according to the American Nuclear Society?s Nuclear Quality Assurance (NQA-1) program [American Society of Mechanical Engineers 1982], with specific levels of software quality assurance (SQA) within NQA-1 applied to each software tool in FORCE. As the tools within FORCE have matured, some integration algorithms to accurately connect the software tools for holistic analysis have been developed and deployed within the FORCE software repository. In accordance with NQA-1 standards, regression tests are required to guarantee the software performs consistently even when new capabilities are added to the software. In this report, we document the deployment of both unit tests, which test the consistent behavior of small pieces of the FORCE code base, as well as integration tests, which test the consistent performance of full use cases for the FORCE integration algorithms. We further document the encapsulation of these tests within a test harness, which collectively checks for each successful test completion on demand. Finally, we document the automation of the test harness using GitHub Actions [GitHub 2024], which require all tests succeed before any new capability or other changes can be added to the FORCE integration software

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

Stability evaluation and mitigation strategies in advanced tokamaks using 3D MHD spectroscopy

Multi-modal, active 3D MHD spectroscopy is applied in high-performance advanced tokamak scenarios to study their stability time evolution, revealing an intriguing dependence on both and . A tailored applied 3D field provides a 3D plasma response to extract the growth rate of the least stable mode. The estimated growth rate finds a decrease in stability when the minimum in the safety factor (q) passes through 2.0 and reveals inherent risks of crossing an additional rational surface at integer q min , even above the usual q = 1 sawtooth condition. Based on this result, the potential scenario in which q min ~ 2 can be safely crossed during a more stable lower β N phase was investigated, and the improved stability of this scenario is confirmed by the estimated growth rate. This shows that 3D MHD spectroscopy can offer insights into strategies for improving stability by identifying the vulnerable aspects of such scenarios. In addition, the method highlights its potential for instability avoidance by enabling early detection of multiple modes, even before magnetic coils can measure them. The measured growth rate by the 3D MHD spectroscopy shows its reliability by exhibiting a correlation with the programmed rises in plasma beta across various high β N and high q min discharges. In addition, this method is successfully applied during rapidly evolving I p ramp-up phases, a key part of the scenario development. By achieving reasonable growth rate measurements at high-performance scenario developments, this technique contributes to the development of advanced diagnostic tools for tokamak scenario stability, which will help identify an effective pathway to stable, high-performance scenarios.

Yang, S. M. [Princeton Plasma Physics Laboratory (↗
DOE OSTI2017

A review of human-system interface design issues observed during analog-to-digital and digital-to-digital migrations in U.S. nuclear power plants - 312

The United States (U.S.) Department of Energy (DOE) Light Water Reactor Sustainability (LWRS) program is developing a scientific basis through targeted research and development (R and D) to support the U.S. nuclear power plant (NPP) fleet in extending their existing licensing period and ensuring their long-term reliability, productivity, safety, and security. Over the last several years, human factors engineering (HFE) professionals at the Idaho National Laboratory (INL) have supported the LWRS Advanced Instrumentation, Information, and Control (II and C) System Technologies pathway across several U.S. commercial NPPs in analog-to-digital migrations (i.e., turbine control systems) and digital-to-digital migrations (i.e., Safety Parameter Display System). These efforts have included in-depth human factors evaluation of proposed human-system interface (HSI) design concepts against established U.S. Nuclear Regulatory Commission (NRC) design guidelines from NUREG-0700, Rev 2 to inform subsequent HSI design prior to transitioning into Verification and Validation. This paper discusses some of the overarching design issues observed from these past HFE evaluations. In addition, this work presents some observed challenges such as common tradeoffs utilities are likely to face when introducing new HSI technologies into NPP hybrid control rooms. The primary purpose of this work is to distill these observed design issues into general HSI design guidance that industry can use in early stages of HSI design. (authors)

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2018

A Systems Biology and Pond Culture-based Understanding and Improvement of Metabolic Processes Related to Productivity in Diverse Microalgal Classes for Viable Biofuel Production

The overarching goal of this project was to understand and manipulate fundamental molecular mechanisms involved in maximizing growth rate and lipid accumulation in diverse classes of microalgae under authentic diurnal conditions to enhance production capabilities for biofuels. The research was aimed at filling two critical knowledge gaps by addressing fundamental cellular issues that govern growth and fuel molecule accumulation in conjunction with realistic climate-simulated cultivation: 1) The insufficient understanding of the effect of metabolic topology on cellular carbon partitioning and its regulation with regards to productivity. 2) The understudied effect of the diurnal and cell cycles on cellular metabolism, resource allocation, and resource mobilization under simulated production conditions. To unravel broader as well as lineage-specific regulatory mechanisms that determine productivity, we compared green algae with diatoms. Complementing the systems approach with a pond-based cultivation method under authentic diurnal conditions, we anticipated an understanding of how the effect of diurnal and cell cycles affects growth and lipid productivity. Elucidation of the topology and regulation of relevant metabolic networks in proposed new model organisms was expected to enable improvements in functional capabilities and biosynthetic pathways. The major goals of the project were achieved by the following accomplishments. Genome assemblies and functional annotations for the green algae S. obliquus strain DOE0152Z and Coleastrella sp. strain DOE0202. Development of a metabolic map for the core carbon metabolism for S. obliquus. Analyzed the cellular topology for the core carbon network and proposed differences in core carbon metabolism for the Chlorophyceae versus the Trebouxiophyceae. Discovered the genes for enzymes involved in dicarboxylic acid metabolism and proposed the existence of C4-type metabolism for S. obliquus. Calculated the energy and reducing equivalencies for TAG and isoprenoid biosynthesis based on the core carbon network created in this project. Identified one newly created strain SOM-P004 (UV-Mutagenesis), which performed better at higher culture densities than wild type in LEAPS reactors under simulated environmental conditions. Results obtained within the course of this project were used in 2017 to apply for a Community Science Program (CSP) at the DOE Joint Genome Institute (JGI). The project (JGI Proposal Id: 503423) with the Title “Comparative genomics and germ plasm diversity in Acutodesmus, a green microalgal bioenergy feedstock candidate with potential for breeding and hybridization.” was selected for CSP 2018 for sequencing of up to 30 genomes of the alga A. obliquus (=S. obliquus). Our genome of the strain DOE0152Z serves as a reference for this new CSP project. Characterization of synchronized cultures of Cyclotella cryptica and the implications on productivity. Determination that some cellular pigments respond to light, but others to the cell cycle. Characterization of productivity of C. cryptica in PNNL ponds. Genome sequence and metabolic mapping of Marinichlorella kaistiae KAS603. Demonstration that some green algae store and utilize starch in the cytoplasm. Photorespiratory pathway clarified in T. pseudonana leading to a better understanding of carbon flux pathways in diatoms. Genome sequence determination, annotation, and comparison completed for C. cryptica, identifying potential metabolic differences that lead to high biomass and lipid accumulation ability for this species. Transcriptomic comparison of silicon (Si) and nitrogen (N) limited triacylglycerol accumulation in Cyclotella cryptica.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

Conserved and plant-unique strategies for overcoming endoplasmic reticulum stress

Stress caused by environmental conditions or physiological growth can lead to an accumulation of unfolded proteins in the endoplasmic reticulum (ER) causing ER stress, which in turn triggers a cytoprotective mechanism termed the unfolded protein response (UPR). Under mild-short stress conditions the UPR can restore ER functioning and cell growth, such as reducing the load of unfolded proteins through the upregulation of genes involved in protein folding and in degrading mis-folded proteins, and through autophagy activation, but it can also lead to cell death under prolonged and severe stress conditions. A diversified suite of sensors has been evolved in the eukaryotic lineages to orchestrate the UPR most likely to suit the cell’s necessity to respond to the different kinds of stress in a conserved as well as species-specific manner. In plants three UPR sensors cooperate with non-identical signaling pathways: the protein kinase inositol-requiring enzyme (IRE1), the ER-membrane-associated transcription factor bZIP28, and the GTP-binding protein β1 (AGB1). In this mini-review, we show how plants differ from the better characterized metazoans and fungi, providing an overview of the signaling pathways of the UPR, and highlighting the overlapping and the peculiar roles of the different UPR branches in light of evolutionary divergences in eukaryotic kingdoms.

54 ENVIRONMENTAL SCIENCES↗