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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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NASA NTRS2019

NASA’s Orbital Debris JAO/ES-MCAT Optical Telescope Facility on Ascension Island

The NASA Orbital Debris Program Office has a long-standing optical program begun over three and a half decades ago in 1984, designed to observe the Earth-orbiting environment with optical telescopes. Photometrically calibrated optical data provides a statistical sample for input to NASA models of the debris population for understanding the current and future debris environment around the Earth. Tracked objects and orbits allow for analysis of break-up events. Both known (correlated target in the SSN catalogue, or CT) and unknown (uncorrelated target, or UCT) objects are of interest to better understand how to protect current spacecraft and design more robust future operational satellites, and advise on how policies and practices can lead to protecting the environment itself for future generations. In 2015, a joint NASA JSC – Air Force Research Labs (AFRL) project culminated in the installation of the 1.3-meter Eugene Stansbery Meter Class Autonomous Telescope, ES-MCAT (a.k.a. MCAT) on Ascension Island. This DFM Engineering designed telescope provides nearly five-times greater light-collecting power than its predecessor, the 0.6-m MODEST telescope, and faster tracking capabilities by both the telescope and the 7-m ObservaDome. This allows for all orbital regimes to be easily within reach, ranging from low Earth to geosynchronous orbits. Extensive testing and commissioning activities of this custom system led to successfully reaching Initial Operational Capability in 2018, and the facility is currently on track to reach Full Operational Capability. The John Africano Observatory (JAO) comprises the primary 1.3-m ES-MCAT facility, the adjacent tower platform with a 0.4-m telescope, a sophisticated suite of weather instruments, and custom software by Euclid Research for autonomously running the entire system, including monitoring the weather and hardware, tasking all components, and collecting, processing, and analyzing the data. The mission of JAO and MCAT will be discussed, including survey and tracking tasking, a full discussion of data calibration, and both optics and weather-dependent performance.

Lederer, S. M.↗
NASA NTRSDate not supplied

Tangerine Dream: Observations of Titan from the Earth

From its discovery in 1655 by the Dutch astronomer Christiaan Huygens, Titan perplexed and confounded Earth-based astronomers for three centuries with its stubborn refusal to yield virtually any clues about its nature. Until the Voyager 1 1980, even fundamentals such as its true diameter, surface pressure, and major atmospheric gas were uncertain [1]. Most of the information we now know about Titan has been wrestled at great expense of time and effort by three spacecraft visitors: Voyager 1, Cassini and Huygens. So why then continue to bother with Earth-based telescopic observations? In this review talk I will describe how significant clues about Titan’s atmospheric composition began to emerge from ground-based observations in the 1940s through 1970s, in the run-up to the revolutionary Voyager 1 flyby. These included the discovery of methane [2], and other significant hydrocarbons including ethane and acetylene in Titan’s stratosphere [3, 4]. Further ground and space-based telescopic work in the 1980s and 1990s revealed the presence of the fourth most abundance gas, carbon monoxide [5], spotted for the first time the bright continent on Titan’s leading hemisphere now known as Xanadu [6], and the comings and goings of bright tropospheric clouds [7]. The Cassini-Huygens mission of 2004-2017 [8, 9] greatly expanded our knowledge of Titan, including the first in situ measurements of the atmosphere and detailed imaging of the surface. However in the two-decades long gap before the next mission, Dragonfly, reaches Titan we are finding new ways to further our knowledge of Titan using the current generation of telescopes and instruments. With high-resolution spectroscopy at infrared and sub-millimeter wavelengths we are finding new chemical constituents in the atmosphere, and even measuring wind fields at middle altitudes. I will conclude by discussing how the next generation of Earth and space-based telescopes and instruments promises yet more breakthroughs via astronomy, including with large aperture 30 and 40 meter class telescopes that will become available in the late 2020s, and spectroscopy with airborne

Titan↗
NASA NTRSDate not supplied

PRECiSA: a static analysis tool for floating-point programs

This presentation introduces PRECiSA, a static analysis framework for analyzing floating-point programs. PRECiSA computes round-off error bounds for a class of floating-point programs, and produces a formal proof certificate of the correctness of these bounds. PRECiSA also has the capability of generating C code which is instrumented to detect unstable branching conditions from a real-number algorithm specification.

Floating-point↗
DOE OSTI2017

Considerations on the Use of Custom Accelerators for Big Data Analytics

Accelerators, including Graphic Processing Units (GPUs) for gen- eral purpose computation, many-core designs with wide vector units (e.g., Intel Phi), have become a common component of many high performance clusters. The appearance of more stable and reliable tools tools that can automatically convert code written in high-level specifications with annotations (such as C or C++) to hardware de- scription languages (High-Level Synthesis - HLS), is also setting the stage for a broader use of reconfigurable devices (e.g., Field Pro- grammable Gate Arrays - FPGAs) in high performance system for the implementation of custom accelerators, helped by the fact that new processors include advanced cache-coherent interconnects for these components. In this chapter, we briefly survey the status of the use of accelerators in high performance systems targeted at big data analytics applications. We argue that, although the progress in the use of accelerators for this class of applications has been sig- nificant, differently from scientific simulations there still are gaps to close. This is particularly true for the ”irregular” behaviors exhibited by no-SQL, graph databases. We focus our attention on the limits of HLS tools for data analytics and graph methods, and discuss a new architectural template that better fits the requirement of this class of applications. We validate the new architectural templates by mod- ifying the Graph Engine for Multithreaded System (GEMS) frame- work to support accelerators generated with such a methodology, and testing with queries coming from the Lehigh University Benchmark (LUBM). The architectural template enables better supporting the task and memory level parallelism present in graph methods by sup- porting a new control model and a enhanced memory interface. We show that out solution allows generating parallel accelerators, pro- viding speed ups with respect to conventional HLS flows. We finally draw conclusions and present a perspective on the use of reconfig- urable devices and Design Automation tools for data analytics.

Data Analytics↗
NASA NTRS2015

NEAs: Phase Angle Dependence of Asteroid Class and Diameter from Observational Studies

We will discuss the results of a planned observation campaign of Near Earth Asteroids (NEAs), 1999 CU3, 2002 GM2, 2002 FG7, and 3691 Bede with instruments on the United Kingdom Infrared Telescope (UKIRT) from 15-Mar-2015 to 28-April 2015 UT. We will study the phase-angle dependence of the reflectance and thermal emission spectra. Recent publications reveal that the assignment of the asteroid class from visible and near-IR spectroscopy can change with phase angle for NEAs with silicate-bearing minerals on their surfaces (S-class asteroids) (Thomas et al. 2014, Icarus 228, 217; Sanchez et al. 2012 Icarus 220, 36). Only three of the larger NEAs have been measured at a dozen phase angles and the trends are not all the same, so there is not yet enough information to create a phase-angle correction. Also, the phase angle effect is not characterized well for the thermal emission including determination of the albedo and the thermal emission. The few NEAs were selected for our study amongst many possible targets based on being able to observe them through a wide range of phase angles, ranging from less than about 10 degrees to greater than 45 degrees over the constrained date range. The orbits of NEAs often generate short observing windows at phase angles higher than 45 deg (i.e., whizzing by Earth and/or close to dawn or dusk). Ultimately, lowering the uncertainty of the translation of asteroid class to meteorite analog and of albedo and size determinations are amongst our science goals. On a few specific nights, we plan to observe the 0.75-2.5 micron spectra with IRTF+SpeX for comparison with UKIRT data including 5-20 micron with UKIRT+UIST/Michelle to determine as best as possible the albedos. To ensure correct phasing of spectroscopic data, we augment with TRAPPIST-telescope light curves and R-band guider image data. Our observations will contribute to understanding single epoch mid-IR and near-IR measurements to obtain albedo, size and IR beaming parameters (the outcomes of thermal models) and asteroid spectral class.

phase-angle↗
DOE OSTI2017

Analysis of hydrogen as a Transportation Fuel FY17 Report

This report summarizes the results of literature reviews, surveys and analyses performed to evaluate the potential of hydrogen-fueled vehicles to be an economically viable transportation alternative. Five existing and important drivers of expanding hydrogen-fueled transportation adoption are multi-billion dollar sales reservations of Nikola Class 8 trucks, CALSTART viability analysis of hybrid-hydrogen drayage trucks in the shipyard cargo application, analysis showing economic advantages of Fuel Cell Electric Vehicles (FCEV)s over Battery Electric Vehicles (BEV)s beginning at 150-mile ranges, the announcement of a commercial 5kg electrolyzer, and commercial plans or vehicle availability by nine vehicle manufacturers of FCEV passenger vehicles. But hydrogen infrastructure availability needed to support broad adoption of hydrogen-fueled vehicles is limited to less than 50 publicly-available refueling stations, primarily in California. The demand side (consumer) economics associated with FCEV adoption showed strong economic sensitivity to the original vehicle’s fuel economy (mpg), distance traveled, and hydrogen (H2) generation costs. Seven use cases were used to evaluate the broad range of potential FCEV purchasers, including autonomous vehicle applications. Each consumer use case analysis resulted in a different hydrogen fuel cost that would be equivalent to the current fuel cost being paid by the consumer. The H2 generation costs (supply side) were sensitive to the volume of H2 supplied and H2 production costs needed to repay H2 supply facility capital costs and produce competitively-priced energy. H2FAST was used to more accurately incorporate capital, maintenance and production costs into a viable H2 supply cost to the consumer. When the H2 generation and consumer economics were combined, several applications with positive economics became clear. The availability of low-cost hydrogen pipeline connections, and therefore low-cost hydrogen, greatly benefits the California drayage truck application with hybrid-hydrogen retrofits being repaid within seven years. Class 8 trucks could also take advantage of these low-cost, but regional hydrogen supplies. In addition, the IVYS electrolyzer-based hydrogen generation product showed the potential to deliver hydrogen economically in an urban or freeway off-ramp setting to a limited number of passenger vehicles in areas with low-cost electricity. These positive, manually developed results show the need to develop more advanced tools to provide an expanded evaluation of the economics of hydrogen-based fuel applications. The use cases evaluated showed significant potential for hydrogen-fueled vehicles to have a sustainable impact as a transportation fuel. The positive impact is not limited to transportation fuels, but also grid resilience and flexibility through the use of controllable and variable electrolyzer output to rapidly adjust to changing grid conditions and enable greater integration of solar and wind generated power. This capability would directly enable alternative fuel vehicles to impact energy consumption, GHG emissions, and the economy at the regional and national levels.

08 HYDROGEN↗
DOE OSTI2018

Beyond Insertion for Na‐Ion Batteries: Nanostructured Alloying and Conversion Anode Materials

Abstract Sodium‐ion technology has the potential to become the next generation of low cost and environmentally friendly electrochemical energy storage system for grid‐level applications. The low cost and abundant raw materials employed in sodium cells have driven the recent increasing interest in sodium‐ion batteries (SIBs), which appear especially appealing, since manufacturers can use the already existing production technology of lithium‐ion batteries. However, SIBs are still an early stage technology, which requires several issues affecting cell performance to be addressed. Despite the accelerated development of cathode materials, anode materials still require further investigation and optimization to reach high energy density performance. In the pursuit of high capacity anode materials, several alloying‐, conversion‐, and combined conversion–alloying‐based electrodes have been investigated. This review offers a comprehensive overview on the recent progresses toward the realization of “beyond‐insertion” anode materials. The role of nanostructuration with the associated advantages and disadvantages is presented for each class of compounds, combined with the main strategies adopted to improve the electrochemical behavior. Finally, an overview of the challenges and perspectives associated with the development of the next generation of anode materials is presented with a particular focus on the role of the electrolyte solutions and solid/electrolyte interphase.

Zhang, Huang↗
DOE OSTI2013

Gamma-ray lines and one-loop continuum from s-channel dark matter annihilations

The era of indirect detection searches for dark matter has begun, with the sensitivities of gamma-ray detectors now approaching the parameter space relevant for weakly interacting massive particles. In particular, gamma ray lines would be smoking gun signatures of dark matter annihilation, although they are typically suppressed compared to the continuum. In this paper, we pay particular attention to the 1-loop continuum generated together with the gamma-ray lines and investigate under which conditions a dark matter model can naturally lead to a line signal that is relatively enhanced. We study generic classes of models in which DM is a fermion that annihilates through an s-channel mediator which is either a vector or scalar and identify the coupling and mass conditions under which large line signals occur. We focus on the ''forbidden channel mechanism'' advocated a few years ago in the ''Higgs in space'' scenario for which tree level annihilation is kinematically forbidden today. Detailed calculations of all 1-loop annihilation channels are provided. We single out very simple models with a large line over continuum ratio and present general predictions for a large range of WIMP masses that are relevant not only for Fermi and Hess II but also for the next generation of telescopes such as CTA and Gamma-400. Constraints from the relic abundance, direct detection and collider bounds are also discussed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

A renewable double plasma mirror for Petawatt-class lasers

Exceptional pulse contrast can be critical for ultraintense laser experiments, particularly when using solid density targets, and their use is becoming widespread. However, current plasma mirror technology is becoming inadequate for the new generation of high repetition rate, high power lasers now available. We describe a novel double plasma mirror configuration based on renewable, free standing, ultrathin liquid crystal films tested at the BELLA Petawatt Laser Center. Although operating at a repetition rate of several shots per minute, this system can be scaled to a high repetition rate exceeding 1 Hz and represents an important step towards enabling sustained, continuous operation of plasma mirrors. We demonstrate an improvement of two to three orders of magnitude in contrast and a total throughput of 80%. We present the first measurements of a beam reflected from a single or double plasma mirror system using a wavefront sensor, showing a well preserved wavefront and spatial mode. Finally, we introduce a model that predicts the total throughput through this double plasma mirror. This is the first model that accurately predicts the peak reflectivity of a plasma mirror when given the laser temporal profile.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Techno Economic Analysis of an LGFCS MWE Class SOFCT System (Final Scientific/Technical Report)

The objective of this project is to perform a range of technical, cost and economic analyses of a MWscale natural gas fired Solid Oxide Fuel Cell (SOFC) distributed power generation system design. The information generated will provide evidence of the tracking of technology and manufacturing readiness supportive of Technology Readiness Level 7 (TRL7) system testing in the 2022 timeframe that meets the Department of Energy’s (DOE) targets for cost (<$6000/kW) and durability (<0.5% power degradation/1000 hours).

20 FOSSIL-FUELED POWER PLANTS↗
NASA NTRS2018

Oceanus: A High Science Return Uranus Orbiter with a Low-Cost Instrument Suite

Ice-giant-sized planets are the most common type of observed exoplanet, yet the two ice giants in our own solar system (Uranus and Neptune) are the least explored class of planet, having only been observed through ground-based observations and a single flyby each by Voyager 2 approximately 30 years ago. These single flybys were unable to characterize the spatial and temporal variability in ice giant magnetospheres, some of the most odd and intriguing magnetospheres in the solar system. They also offered only limited constraints on the internal structure of ice giants; understanding the internal structure of a planet is important for understanding its formation and evolution. The most recent planetary science Decadal Survey by the U.S. National Academy of Sciences, ''Vision and Voyages for Planetary Science in the Decade 2013-2022,'' identified the ice giant Uranus as the third highest priority for a Flagship mission in the decade 2013-2022. However, in the event that NASA or another space agency is unable to fly a Flagship-class mission to an ice giant in the next decade, this paper presents a mission concept for a focused, lower cost Uranus orbiter called OCEANUS (Origins and Composition of the Exoplanet Analog Uranus System). OCEANUS would increase our understanding of the interior structure of Uranus, its magnetosphere, and how its magnetic field is generated. These goals could be achieved with just a magnetometer and the spacecraft's radio system. This study shows that several of the objectives outlined by the Decadal Survey, including one of the two identified as highest priority, are within reach for a New-Frontiers-class mission.

Elder, C. M.↗
DOE OSTI2024

Nonsteady Load Responses of Wind Turbines to Atmospheric and Mountain-Generated Turbulence Eddies, With Impacts on the Main Bearing: A Validation Study

Previous computational and field experiments identify three characteristic time scales in the aerodynamic responses of utility-scale wind turbine loads to atmospheric boundary layer (ABL) turbulence: a 30-90 second time scale for the passage of high/low speed "streaks" through the rotor plane, the blade and rotor rotation time scales (approximately 1 to 5 seconds), and a sub-second time scale created by blade rotation through gradients within eddy coherent structure. In the current study we compare aerodynamic load responses from daytime ABL turbulence quantified with large-eddy simulation and a actuator line model of the NREL 5 MW wind turbine with analysis of field data from the NREL/GE 1.5 MW wind turbine 5 kilometers east of the Rocky Mountain Front Range in Colorado. In addition, we contrast the responses to the passage of the mountain-generated eddies embedded within the westerly winds with the ABL eddies embedded within northerly/southerly winds. These analyses are in context with the nonsteady forcing of the main bearing by the aerodynamic generation of nontorque bending moments on the main shaft. Potentially relevant to main bearing failure mechanisms, both computational and field data show that the magnitudes of turbulence-generated nontorque bending moments, that we show generate nonsteady force on the main bearing, are of order, and often larger than, torque (which underlies power). However, the temporal variations in these two responses are uncorrelated, implying that the aerodynamic mechanisms that drive power and main bearing response are fundamentally different. We find this to be the case in the field with both mountain-generated eddies (westerly winds) and ABL-generated eddies (northerly/southerly winds). Whereas the time and length scales are comparable, the mountain eddies were somewhat more energetic than the northerly/southerly ABL eddies. Interestingly, however, the fluctuations in nontorque bending moment that force the main bearing were found to be stronger when forced by the ABL eddies than the mountain eddies. The field studies validate the key results from the computational study and show even stronger response in the nontorque bending moment than in the computer simulations. In all cases, the torque and nontorque bending moments are temporally uncorrelated, torque and power are driven by time variations in rotor-averaged horizontal wind velocity and nontorque bending moments are driven by time changes in the degree of nonuniformity in the distribution of velocity over the rotor plane. Thus the results generalize the mechanisms underlying nonsteady aerodynamic forcing to classes of turbulence eddy types with strength of order or stronger than ABL eddies with transverse scale of order the wind turbine rotor. These include atmospheric turbulence eddies, topography-generated turbulence eddies and, by extension, impacts of turbine-wake-scale turbulence eddies on downstream wind turbine rotors.

17 WIND ENERGY↗
DOE OSTI2025

When Pore Met Semi: Charting the Rise of Porous Metal Halide Semiconductors

Metal halide semiconductors (MHS) are a versatile class of materials with fully customizable mechanical and optoelectronic properties that have proven to be prominent candidates in numerous impactful applications. Finding a way to generate porosity in MHS would bestow upon them an additional node in property engineering, thus allowing them to be utilized in uncharted technologies. Motivated by this promise, we developed a general strategy to render the MHS porous. We employed molecular cages as structure-directing agents and countercations, which fostered a new family of materials: porous metal halide semiconductors (PMHS). The presence of molecular cages gave rise to ultramicroporous structures imposed by the organic part cavities and a record water stability performance of 27 months so far. In this Perspective, we discuss the principles and promises of PMHS, which combine the merits of porous and electronic compounds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Synthesis-driven, structure-dependent optical behavior in phase-tunable NaYF 4 :Yb,Er-based motifs and associated heterostructures

Understanding the key parameters necessary for generating uniform Er,Yb co-activated NaYF 4 possessing various selected phases (i.e. cubic or hexagonal) represents an important chemical strategy towards tailoring optical behavior in these systems. In this paper, we report on a straightforward hydrothermal synthesis in which the separate effects of reaction temperature, reaction time, and precursor stoichiometry in the absence of any surfactant were independently investigated. Interestingly, the presence and the concentration of NH 4 OH appear to be the most critical determinants of the phase and morphology. For example, with NH 4 OH as an additive, we have observed the formation of novel hierarchical nanowire bundles which possess overall lengths of ~5 μm and widths of ~1.5 μm but are composed of constituent component sub-units of long, ultrathin (~5 nm) nanowires. These motifs have yet to be reported as distinctive morphological manifestations of fluoride materials. The optical properties of as-generated structures have also been carefully analyzed. Specifically, we have observed tunable, structure-dependent energy transfer behavior associated with the formation of a unique class of NaYF 4 –CdSe quantum dot (QD) heterostructures, incorporating zero-dimensional (0D), one-dimensional (1D), and three-dimensional (3D) NaYF 4 structures. Our results have demonstrated the key roles of the intrinsic morphology-specific physical surface area and porosity as factors in governing the resulting opto-electronic behavior. Finally and specifically, the trend in energy transfer efficiency correlates well with the corresponding QD loading within these heterostructures, thereby implying that the efficiency of FRET appears to be directly affected by the amount of QDs immobilized onto the external surfaces of the underlying fluoride host materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Feynman formulae and phase space Feynman path integrals for tau-quantization of some Lévy-Khintchine type Hamilton functions

Evolution semigroups generated by pseudo-differential operators are considered. These operators are obtained by different (parameterized by a number τ) procedures of quantization from a certain class of functions (or symbols) defined on the phase space. This class contains Hamilton functions of particles with variable mass in magnetic and potential fields and more general symbols given by the Lévy-Khintchine formula. The considered semigroups are represented as limits of n-fold iterated integrals when n tends to infinity. Such representations are called Feynman formulae. Some of these representations are constructed with the help of another pseudo-differential operator, obtained by the same procedure of quantization; such representations are called Hamiltonian Feynman formulae. Some representations are based on integral operators with elementary kernels; these are called Lagrangian Feynman formulae. Langrangian Feynman formulae provide approximations of evolution semigroups, suitable for direct computations and numerical modeling of the corresponding dynamics. Hamiltonian Feynman formulae allow to represent the considered semigroups by means of Feynman path integrals. In the article, a family of phase space Feynman pseudomeasures corresponding to different procedures of quantization is introduced. The considered evolution semigroups are represented as phase space Feynman path integrals with respect to these Feynman pseudomeasures, i.e., different quantizations correspond to Feynman path integrals with the same integrand but with respect to different pseudomeasures. This answers Berezin’s problem of distinguishing a procedure of quantization on the language of Feynman path integrals. Moreover, the obtained Lagrangian Feynman formulae allow also to calculate these phase space Feynman path integrals and to connect them with some functional integrals with respect to probability measures.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Multidimensional smooth loops with universal elasticity

Let E-tilde be a universal (isotopically invariant) identity that is derived from the elasticity identity E:(xy)x=x(yx). One of the authors has previously shown that a) each local loop of dimension r with identity E-tilde (briefly, a loop E-tilde ) is a smooth middle Bol loop of dimension r; b) smooth two-dimensional loops E-tilde are Lie groups; c) up to isotopy, there exist only two three-dimensional loops E-tilde : the loops E{sub 1} and E{sub 2}. In this paper, the loops E{sub 1} and E{sub 2} are extended to the multidimensional case. The fact that each smooth loop E-tilde of dimension r corresponds to a unique multidimensional three-web on a manifold of dimension 2r is key to our work. In addition, the class of loops under investigation is characterized by the fact that the torsion tensor of the corresponding web has rank 1 (that is, the algebra generated by this tensor has a one-dimensional derived algebra). This enables us to express the differential equations of the problem in an invariant form. The system of equations thus obtained was found to be amenable to integration in the most general case, and the equations of the required loops have been obtained in local coordinates. Bibliography: 17 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

Theory of Defect-Induced Crystal Field Perturbations in Rare-Earth Magnets

We present a theory describing the single-ion anisotropy of rare-earth (RE) magnets in the presence of point defects. Taking the RE-lean 1 ∶ 12 magnet class as a prototype, we use first-principles calculations to show how the introduction of Ti substitutions into SmFe 12 perturbs the crystal field, generating new coefficients due to the lower symmetry of the RE environment. We then demonstrate that these perturbations can be described extremely efficiently using a screened point charge model. We provide analytical expressions for the anisotropy energy that can be straightforwardly implemented in atomistic spin dynamics simulations, meaning that such simulations can be carried out for an arbitrary arrangement of point defects. The significant crystal field perturbations calculated here demonstrate that a sample that is single phase from a structural point of view can nonetheless have a dramatically varying anisotropy profile at the atomistic level if there is compositional disorder, which may influence localized magnetic objects like domain walls or skyrmions. Published by the American Physical Society 2024

25 ENERGY STORAGE↗
DOE OSTI2019

Systems-Level Analysis of Oxygen Exposure in Zymomonas mobilis : Implications for Isoprenoid Production

ABSTRACT Zymomonas mobilis is an aerotolerant anaerobe and prolific ethanologen with attractive characteristics for industrial bioproduct generation. However, there is currently insufficient knowledge of the impact that environmental factors have on flux through industrially relevant biosynthetic pathways. Here, we examined the effect of oxygen exposure on metabolism and gene expression in Z. mobilis by combining targeted metabolomics, mRNA sequencing, and shotgun proteomics. We found that exposure to oxygen profoundly influenced metabolism, inducing both transient metabolic bottlenecks and long-term metabolic remodeling. In particular, oxygen induced a severe but temporary metabolic bottleneck in the methyl erythritol 4-phosphate pathway for isoprenoid biosynthesis caused by oxidative damage to the iron-sulfur cofactors of the final two enzymes in the pathway. This bottleneck was resolved with minimal changes in expression of isoprenoid biosynthetic enzymes. Instead, it was associated with pronounced upregulation of enzymes related to iron-sulfur cluster maintenance and biogenesis (i.e., flavodoxin reductase and the suf operon). We also detected major changes in glucose utilization in the presence of oxygen. Specifically, we observed increased gluconate production following exposure to oxygen, accounting for 18% of glucose uptake. Our results suggest that under aerobic conditions, electrons derived from the oxidation of glucose to gluconate are diverted to the electron transport chain, where they can minimize oxidative damage by reducing reactive oxygen species such as H 2 O 2 . This model is supported by the simultaneous upregulation of three membrane-bound dehydrogenases, cytochrome c peroxidase, and a cytochrome bd oxidase following exposure to oxygen. IMPORTANCE Microbially generated biofuels and bioproducts have the potential to provide a more environmentally sustainable alternative to fossil-fuel-derived products. In particular, isoprenoids, a diverse class of natural products, are chemically suitable for use as high-grade transport fuels and other commodity molecules. However, metabolic engineering for increased production of isoprenoids and other bioproducts is limited by an incomplete understanding of factors that control flux through biosynthetic pathways. Here, we examined the native regulation of the isoprenoid biosynthetic pathway in the biofuel producer Zymomonas mobilis . We leveraged oxygen exposure as a means to perturb carbon flux, allowing us to observe the formation and resolution of a metabolic bottleneck in the pathway. Our multi-omics analysis of this perturbation enabled us to identify key auxiliary enzymes whose expression correlates with increased production of isoprenoid precursors, which we propose as potential targets for future metabolic engineering.

59 BASIC BIOLOGICAL SCIENCES↗