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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Incorporation of salinity, nitrogen, and shading stress factors into the Huesemann Algae Biomass Growth model

The Huesemann Algae Biomass Growth (HABG) model predicts microalgae biomass growth in outdoor raceways as a function of water temperature and incident light intensity. The model over-predicted growth in several Regional Algal Feedstock Testbed (RAFT) experiments. Inspection of the culture conditions suggested that salinity stress, nutrient limitation, and shading reduced growth, which were not included in the original model. Laboratory experiments were carried out to measure growth response of S. obliquus to high salinity and limited nitrogen. In addition, the shading effect was estimated based on raceway geometry, solar angle, albedo and measured light intensity data. In this study, the improvement of model performance is presented step by step as each growth limiting factor is incorporated into the model. The new salinity, shanding, and nutrient stress factors remove most of the over-prediction of the original model. Comparison of the model with observed data indicated that ignoring the lag phase also resulted in overprediction. Delaying the start of the simulation until the end of the lag phase and inclusion of stress factors lowered model inaccuracy from 90% over-prediction to within ±10% in six out of seven batches.

09 BIOMASS FUELS↗
DOE OSTI2016

Measurement of D s + production and nuclear modification factor in Pb-Pb collisions at $ \sqrt{{\mathrm{s}}_{\mathrm{NN}}}=2.76 $

Here, the production of prompt D s + mesons was measured for the first time in collisions of heavy nuclei with the ALICE detector at the LHC. The analysis was performed on a data sample of Pb-Pb collisions at a centre-of-mass energy per nucleon pair, √s NN , of 2.76 TeV in two different centrality classes, namely 0–10% and 20–50%. Ds+ mesons and their antiparticles were reconstructed at mid-rapidity from their hadronic decay channel D s + → Φπ + , with Φ → K – K + , in the transverse momentum intervals 4 < pT < 12GeV/c and 6 < pT < 12 GeV/c for the 0–10% and 20–50% centrality classes, respectively. The nuclear modification factor RAA was computed by comparing the pT-differential production yields in Pb-Pb collisions to those in proton-proton (pp) collisions at the same energy. This pp reference was obtained using the cross section measured at √s = 7 TeV and scaled to √s = 2.76 TeV. The RAA of D s + mesons was compared to that of non-strange D mesons in the 10% most central Pb-Pb collisions. At high p T (8 < p T < 12 GeV/c) a suppression of the D s + -meson yield by a factor of about three, compatible within uncertainties with that of non-strange D mesons, is observed. At lower p T (4 < p T < 8 GeV/c) the values of the D s + -meson R AA are larger than those of non-strange D mesons, although compatible within uncertainties. The production ratios D s + /D 0 and D s + /D + were also measured in Pb-Pb collisions and compared to their values in proton-proton collisions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Transcription Factors Controlling the Rhizobium–Legume Symbiosis: Integrating Infection, Organogenesis and the Abiotic Environment

Abstract Legume roots engage in a symbiotic relationship with rhizobia, leading to the development of nitrogen-fixing nodules. Nodule development is a sophisticated process and is under the tight regulation of the plant. The symbiosis initiates with a signal exchange between the two partners, followed by the development of a new organ colonized by rhizobia. Over two decades of study have shed light on the transcriptional regulation of rhizobium–legume symbiosis. A large number of transcription factors (TFs) have been implicated in one or more stages of this symbiosis. Legumes must monitor nodule development amidst a dynamic physical environment. Some environmental factors are conducive to nodulation, whereas others are stressful. The modulation of rhizobium–legume symbiosis by the abiotic environment adds another layer of complexity and is also transcriptionally regulated. Several symbiotic TFs act as integrators between symbiosis and the response to the abiotic environment. In this review, we trace the role of various TFs involved in rhizobium–legume symbiosis along its developmental route and highlight the ones that also act as communicators between this symbiosis and the response to the abiotic environment. Finally, we discuss contemporary approaches to study TF-target interactions in plants and probe their potential utility in the field of rhizobium–legume symbiosis.

Cell Biology↗
DOE OSTI2020

Two interacting ethylene response factors regulate heat stress response

Abstract The ethylene response factor (ERF) transcription factors are integral components of environmental stress signaling cascades, regulating a wide variety of downstream genes related to stress responses and plant development. However, the mechanisms by which ERF genes regulate the heat stress response are not well understood. Here, we uncover the positive role of ethylene signaling, ERF95 and ERF97 in basal thermotolerance of Arabidopsis thaliana. We demonstrate that ethylene signaling-defective mutants exhibit compromised basal thermotolerance, whereas plants with constitutively activated ethylene response show enhanced basal thermotolerance. EIN3 physically binds to the promoters of ERF95 and ERF97. Ectopic constitutive expression of ERF95 or ERF97 increases the basal thermotolerance of plants. In contrast, erf95 erf96 erf97 erf98 quadruple mutants exhibit decreased basal thermotolerance. ERF95 and ERF97 genetically function downstream of EIN3. ERF95 can physically interact with ERF97, and this interaction is heat inducible. ERF95 and ERF97 regulate a common set of target genes, including known heat-responsive genes and directly bind to the promoter of HSFA2. Thus, our study reveals that the EIN3-ERF95/ERF97-HSFA2 transcriptional cascade may play an important role in the heat stress response, thereby establishing a connection between ethylene and its downstream regulation in basal thermotolerance of plants.

Biochemistry & Molecular Biology↗
DOE OSTI2024

QCD Predictions for Meson Electromagnetic Form Factors at High Momenta: Testing Factorization in Exclusive Processes

We report the first lattice QCD computation of pion and kaon electromagnetic form factors, 𝐹 𝑀⁡ (𝑄 2 ), at large momentum transfer up to 10 and 28 GeV 2 , respectively. Utilizing physical masses and two fine lattices, we achieve good agreement with JLab experimental results at 𝑄 2 ≲ 4 GeV 2 . For 𝑄 2 ≳ 4 GeV 2 , our results provide ab initio QCD benchmarks for the forthcoming experiments at JLab 12 GeV and future electron-ion colliders. We also test the QCD collinear factorization framework utilizing our high-𝑄 2 form factors at next-to-next-to-leading order in perturbation theory, which relates the form factors to the leading Fock-state meson distribution amplitudes. Comparisons with independent lattice QCD calculations using the same framework demonstrate, within estimated uncertainties, the universality of these nonperturbative quantities.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

A Numerical Study of Factors Affecting Fracture-Fluid Cleanup and Produced Gas/Water in Marcellus Shale: Part II

Horizontal wells combined with successful multi-stage hydraulic fracture treatments are currently the most established method for effectively stimulating and enabling economic development of gas bearing organic-rich shale formations. Fracture cleanup in the Stimulated Reservoir Volume (SRV) is critical to stimulation effectiveness and long-term well performance. However, fluid cleanup is often hampered by formation damage, and post-fracture well performance frequently falls below expectations. A systematic study of the factors that hinder fracture fluid cleanup in shale formations can help optimize fracture treatments and better quantify long term volumes of produced water and gas. Fracture fluid cleanup is a complex process influenced by multi-phase flow through porous media (relative permeability hysteresis, capillary pressure etc.), reservoir rock and fluid properties, fracture fluid properties, proppant placement, fracture treatment parameters, and subsequent flowback and field operations. Changing SRV and fracture conductivity as production progresses further adds to the complexity of this problem. Numerical simulation is the best, and most practical approach to investigate such a complicated blend of mechanisms, parameters, their interactions, and subsequent impact on fracture fluid cleanup and well deliverability. In this paper, a 3-dimensional, 2-phase, dual-porosity model was used to investigate the impact of multiphase flow, proppant crushing, proppant diagenesis, shut-in time, reservoir rock compaction, gas slippage, and gas desorption on fracture fluid cleanup, and well performance in Marcellus shale. The research findings have shed light on the factors that substantially constrains efficient fracture fluid cleanup in gas shales, and provided guidelines for improved fracture treatment designs and water management.

58 GEOSCIENCES↗
DOE OSTI2022

Air Exchange Rate Impact on Activity Equilibrium Factors and Inhalation Fractional Equilibrium Factors for Rn, Xe, Kr, Ar, Ne, and Their Progeny in Vapor Intrusion, Risk, and Dose Models

Exposure to the radioactive noble gasses, especially radon, is of high concern and poses a significant risk to humans in an indoor air environment as the second leading cause of lung cancer in the United States. To evaluate and minimize the risks posed by these gasses, it is important to understand their radiological and physical properties. The EPA’s Radon Vapor Intrusion Screening Level (RVISL) calculator calculates indoor air RVISLs based on target working levels (WLs), target excess lifetime cancer risk (ELCR), and annual dose limits for the actinon (Rn-219), thoron (Rn-220), and radon (Rn-222) decay series. The RVISLs are based on inhalation and submersion in gas cloud exposure routes for residential and commercial settings. The RVISLs are analogous to preliminary remediation goals (PRGs) and dose compliance concentrations (DCCs), where the isotope-specific values are in units of activity concentration (activity per unit volume). If the concentration of a parent isotope of radon or its progeny is found to exceed the RVISL, then further action to ensure cleanup of the contaminant may be necessary. In residential and commercial settings, the RVISLs will vary based on the air exchange rate present. The EPA’s Radionuclide PRG and DCC Calculators also assess the risk/dose from noble gases in the air due to household use of water like showering. In this study, a computational method in MATLAB was developed to determine the impact of the air exchange rate on the activity equilibrium factor (A eq ) and the inhalation fractional equilibrium factor (F eq ). Both factors are values that reflect the equilibrium concentrations of progeny to their parent in the air. These factors have a direct impact on the RVISL, PRG, and DCC calculations of WL, ELCR, and annual dose, respectively. This study builds on a previous report that only focused on actinon, thoron, and radon by revisiting the original A eq and F eq calculation methods, as well as including the values for the Rn-207, Rn-209, Rn-210, Rn-211, Rn-215, Rn-216, Rn-217, Rn-218, Rn-223, Ne-24, Ar-42, Ar-43, Ar-44, Kr-74, Kr-75, Kr-76, Kr-77, Kr-88, Kr-89, Xe-120, Xe-121, Xe-122, Xe-123, Xe-135m, and Xe-138 decay chains, which are not currently available in literature. The EPA’s RVISL calculator will be updated to include the new A eq and F eq values for the actinon, thoron, and radon decay chains, while the rest of the calculators will incorporate all the new A eq and F eq values as appropriate.

63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTAN↗
DOE OSTI2016

Biota Modeling in EPA’s Preliminary Remediation Goal and Dose Compliance Concentration Calculators for Use in EPA Superfund Risk Assessment: Explanation of Intake Rate Derivation, Transfer Factor Compilation, and Mass Loading Factor Sources

The Preliminary Remediation Goal (PRG) and Dose Compliance Concentration (DCC) calculators are screening level tools that set forth Environmental Protection Agency’s (EPA) recommended approaches, based upon currently available information with respect to risk assessment, for response actions at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) sites, commonly known as Superfund. The screening levels derived by the PRG and DCC calculators are used to identify isotopes contributing the highest risk and dose as well as establish preliminary remediation goals. Each calculator has a residential gardening scenario and subsistence farmer exposure scenarios that require modeling of the transfer of contaminants from soil and water into various types of biota (crops and animal products). New publications of human intake rates of biota; farm animal intakes of water, soil, and fodder; and soil to plant interactions require updates be implemented into the PRG and DCC exposure scenarios. Recent improvements have been made in the biota modeling for these calculators, including newly derived biota intake rates, more comprehensive soil mass loading factors (MLFs), and more comprehensive soil to tissue transfer factors (TFs) for animals and soil to plant transfer factors (BV’s). New biota have been added in both the produce and animal products categories that greatly improve the accuracy and utility of the PRG and DCC calculators and encompass greater geographic diversity on a national and international scale.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Pd 2 Se 3 Monolayer: A Promising Two-Dimensional Thermoelectric Material with Ultralow Lattice Thermal Conductivity and High Power Factor

A high power factor and low lattice thermal conductivity are two essential ingredients of highly efficient thermoelectric materials. Although monolayers of transition-metal dichalcogenides possess high power factors, high lattice thermal conductivities significantly impede their practical applications. Our first-principles calculations show that these two ingredients are well fulfilled in the recently synthesized Pd 2 Se 3 monolayer, whose crystal structure is composed of [Se 2 ] 2- dimers, Se 2- anions, and Pd 2+ cations coordinated in a square-planar manner. Our detailed analysis of third-order interatomic force constants reveals that the anharmonicity and soft phonon modes associated with covalently bonded [Se 2 ] 2- dimers lead to ultralow lattice thermal conductivities in Pd 2 Se 3 monolayers (1.5 and 2.9 W m -1 K -1 along the a- and b-axes at 300 K, respectively), which are comparable to those of high-performance bulk thermoelectric materials such as PbTe. Moreover, the “pudding-mold” type band structure, caused by Pd 2+ (d 8 ) cations coordinated in a square-planar crystal field, leads to high power factors in Pd 2 Se 3 monolayers. Consequently, both electron- and hole-doped thermoelectric materials with a considerably high zT can be achieved at moderate carrier concentrations, suggesting that Pd 2 Se 3 is a promising two-dimensional thermoelectric material. Our results suggest that hierarchical chemical bonds, that is, coexistence of different types of chemical bonds, combined with a square-planar crystal field is a promising route for designing high-efficiency thermoelectric materials.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Stand development and other intrinsic factors largely control fine-root dynamics with only subtle modifications from resource availability

Forest productivity depends on resource acquisition by ephemeral roots and leaves. A combination of intrinsic and environmental factors influences ephemeral organs; however, difficulties in studying belowground organs impede mechanistic understanding of fine-root production and turnover. To quantify factors controlling fine-root dynamics, we grew a deciduous hardwood (Populus deltoides Bartr.) and an evergreen conifer (Pinus taeda L.) with distinct soil moisture and nutrient availability treatments. We monitored fine-root dynamics with minirhizotrons for 6 years during early stand development and expressed results on a root length, biomass and mortality-risk basis. Stand development and other intrinsic factors consistently influenced both species in the same direction and by similar magnitude. Live-root length increased to a peak during establishment and slowly declined after roots of neighboring trees overlapped. Root longevity was highest during establishment and decreased thereafter. Root longevity consistently increased with depth of appearance and initial root diameter. Season of appearance affected root longevity in the following order: spring > summer > fall > winter. The influence of soil resource availability on fine-root dynamics was inconsistent between species, and ranked below that of rooting depth, initial diameter, stand development and phenology. Fine-root biomass either increased or was unaffected by greater resource availability. Fine-root production and live root length decreased with irrigation for both species, and increased with fertilization only for poplar. Fine-root mortality risk both increased and decreased depending on species and amendment treatment. Differing responses to soil moisture and nutrient availability between species suggests we should carefully evaluate generalizations about the response of fine-root dynamics to resource availability. Finally, while attempting to describe and explain carbon allocation to fine-root production and turnover, modelers and physiologists should first consider consistent patterns of allocation caused by different depth, diameter, stand development, phenology and species before considering allocation due to soil resource availability.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

SU-F-T-572: Small Fields Output Factors Measurement and Correction Factor Determination for Several Active and Passive Detectors

Purpose: To measure the output factor (OF) and output correction factors (OCF) of small circular cones using various active and passive detectors. Methods: The OF of BrainLab circular cones of 4, 6, 7.5, 10, 12.5 and 15mm diameter were measured isocentrically at 15mm depth for 6 MV X-rays at 1000 MU/min from Novalis-Tx Linac using high resolution diodes (SFD, Edge, PTW60008), plastic scintillator (ExtradinW1), small ionization chamber (CC01), EBT3 film and Al2O3:C OSLDs (nanoDot). OCF was calculated as a ratio of the OF of each detector relative to EBT3. Long term overall measurement uncertainty were estimated from the 15 repeat measurement performed for each detector over a period of 1year Results: The mean OF measured using various detectors are shown in the figure. In comparison to EDR3 measurement, nanoDot, CC01 and ExtradinW1 showed consistently lower OF upto −25.7% (nanoDot) which gradually improves with cone size (Table). The variation in OF measure with CC01 and ExtradinW1 for cone size >10mm is within −1.4% and −1.9%. Whereas, Edge and PTW60008 measured consistently larger OF except for 4mm cone. All diodes showed better agreement with EDR3 with maximum variation within ±1.7% (SFD), 2.5% (Edge) and 4.4% (PTW60008). The OCF was largest for nanoDot (range 1.04–1.35) and least for the diodes (range 0.97–1.04). The estimated overall long term standard uncertainty (k=2, 95% confidence) were highest for nanoDot at 3% followed by 2.43% for EDR3, 1% for SFD, 0.49% for ExtradinW1, 0.42% for CC01 and PTW60008, 0.16% for edge. Conclusion: Largest OF for the smallest cone was observed from EDR3. Although correction factor needed for all diodes were very similar, Edge showed most consistent result. nanoDot in its present form is not suitable for OF measurement from small fields. ExtradinW1 with its stem oriented perpendicular to beam axis underestimate OF for field size ≤10mm and need further investigation.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Biota Modeling in EPA’s Preliminary Remediation Goal and Dose Compliance Concentration Calculators for Use in EPA Superfund Risk Assessment: Explanation of Intake Rate Derivation, Transfer Factor Compilation, and Mass Loading Factor Sources

The Preliminary Remediation Goal (PRG) and Dose Compliance Concentration (DCC) calculators are screening level risk assessment tools that set forth the Environmental Protection Agency’s (EPA) recommended approaches and currently available risk assessment guidance for response actions at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) sites, commonly known as Superfund. The environmental screening levels derived by the PRG and DCC calculators are used to identify isotopes contributing the highest risk and dose as well as establish preliminary remediation goals. Each calculator has residential gardening and subsistence farmer exposure scenarios that model transfer of contaminants from soil and water into various types of biota (crops and animal products). New publications of human intake rates of biota; farm animal intakes of water, soil, and fodder; and soil to plant interactions require updates be implemented into the PRG and DCC calculators. Recent improvements in the biota modeling for these calculators include newly derived biota intake rates, enhanced soil mass loading factors (MLFs), and more comprehensive soil to plant transfer factors (BV’s) and soil to tissue transfer factors (TFs) for animals. New biota have been added in both the produce and animal products categories that greatly improve the accuracy and utility of the PRG and DCC calculators and encompass greater geographic diversity on a national and international scale.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Low-rank factorization of electron integral tensors and its application in electronic structure theory

In this letter, we introduce the reverse Cuthill-McKee (RCM) algorithm, which is often used for the bandwidth reduction of sparse tensors, to transform the two-electron integral tensors to their block diagonal forms. By further applying the pivoted Cholesky decomposition (CD) on each of the diagonal blocks, we are able to represent the high-dimensional two-electron integral tensors in terms of permutation matrices and low-rank Cholesky vectors. This representation facilitates the low-rank factorization of the high-dimensional tensor contractions that are usually encountered in post-Hartree-Fock calculations. In this letter, we discuss the second-order Møller-Plesset (MP2) method and linear coupled- cluster model with doubles (L-CCD) as two simple examples to demonstrate the efficiency of the RCM-CD technique in representing two-electron integrals in a compact form.

electronic structure theory↗
DOE OSTI2022

An expanded role for the transcription factor WRINKLED1 in the biosynthesis of triacylglycerols during seed development

The transcription factor WRINKLED1 ( WRI1 ) is known as a master regulator of fatty acid synthesis in developing oilseeds of Arabidopsis thaliana and other species. WRI1 is known to directly stimulate the expression of many fatty acid biosynthetic enzymes and a few targets in the lower part of the glycolytic pathway. However, it remains unclear to what extent and how the conversion of sugars into fatty acid biosynthetic precursors is controlled by WRI 1. To shortlist possible gene targets for future in-planta experimental validation, here we present a strategy that combines phylogenetic foot printing of cis-regulatory elements with additional layers of evidence. Upstream regions of protein-encoding genes in A. thaliana were searched for the previously described DNA-binding consensus for WRI1, the ASML1/WRI1 (AW)-box. For about 900 genes, AW-box sites were found to be conserved across orthologous upstream regions in 11 related species of the crucifer family. For 145 select potential target genes identified this way, affinity of upstream AW-box sequences to WRI1 was assayed by Microscale Thermophoresis. This allowed definition of a refined WRI1 DNA-binding consensus. We find that known WRI1 gene targets are predictable with good confidence when upstream AW-sites are phylogenetically conserved, specifically binding WRI1 in the in vitro assay, positioned in proximity to the transcriptional start site, and if the gene is co-expressed with WRI1 during seed development. When targets predicted in this way are mapped to central metabolism, a conserved regulatory blueprint emerges that infers concerted control of contiguous pathway sections in glycolysis and fatty acid biosynthesis by WRI1. Several of the newly predicted targets are in the upper glycolysis pathway and the pentose phosphate pathway. Of these, plastidic isoforms of fructokinase ( FRK 3) and of phosphoglucose isomerase ( PGI 1) are particularly corroborated by previously reported seed phenotypes of respective null mutations.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

The trypanocidal benznidazole promotes adaptive response to oxidative injury: Involvement of the nuclear factor-erythroid 2-related factor-2 (Nrf2) and multidrug resistance associated protein 2 (MRP2)

Oxidative stress is a frequent cause underlying drug-induced hepatotoxicity. Benznidazole (BZL) is the only trypanocidal agent available for treatment of Chagas disease in endemic areas. Its use is associated with side effects, including increases in biomarkers of hepatotoxicity. However, BZL potential to cause oxidative stress has been poorly investigated. Here, we evaluated the effect of a pharmacologically relevant BZL concentration (200 μM) at different time points on redox status and the counteracting mechanisms in the human hepatic cell line HepG2. BZL increased reactive oxygen species (ROS) after 1 and 3 h of exposure, returning to normality at 24 h. Additionally, BZL increased glutathione peroxidase activity at 12 h and the oxidized glutathione/total glutathione (GSSG/GSSG + GSH) ratio that reached a peak at 24 h. Thus, an enhanced detoxification of peroxide and GSSG formation could account for ROS normalization. GSSG/GSSG + GSH returned to control values at 48 h. Expression of the multidrug resistance-associated protein 2 (MRP2) and GSSG efflux via MRP2 were induced by BZL at 24 and 48 h, explaining normalization of GSSG/GSSG + GSH. BZL activated the nuclear erythroid 2-related factor 2 (Nrf2), already shown to modulate MRP2 expression in response to oxidative stress. Nrf2 participation was confirmed using Nrf2-knockout mice in which MRP2 mRNA expression was not affected by BZL. In summary, we demonstrated a ROS increase by BZL in HepG2 cells and a glutathione peroxidase- and MRP2 driven counteracting mechanism, being Nrf2 a key modulator of this response. Our results could explain hepatic alterations associated with BZL therapy. - Highlights: • BZL triggers a redox imbalance in the human hepatic cell line HepG2. • Concomitantly BZL triggers compensatory mechanisms to alleviate the redox injury. • Response mechanisms comprise an enhanced glutathione peroxidase and MRP2 activity. • Transcription factor Nrf2 plays a key role orchestrating compensatory mechanisms.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

A microbial sensor for organophosphate hydrolysis exploiting an engineered specificity switch in a transcription factor

A whole-cell biosensor utilizing a transcription factor (TF) is an effective tool for sensitive and selective detection of specialty chemicals or anthropogenic molecules, but requires access to an expanded repertoire of TFs. Using homology modeling and ligand docking for binding pocket identification, assisted by conservative mutations in the pocket, we engineered a novel specificity in an Acinetobacter TF, PobR, to ‘sense’ a chemical p-nitrophenol (pNP) and measured the response via a fluorescent protein reporter expressed from a PobR promoter. Out of 107 variants of PobR, four were active when dosed with pNP, with two mutants showing a specificity switch from the native effector 4-hydroxybenzoate (4HB). One of the mutants, pNPmut1 was then used to create a smart microbial cell responding to pNP production from hydrolysis of an insecticide, paraoxon, in a coupled assay involving phosphotriesterase (PTE) enzyme expressed from a separate promoter. We show the fluorescence of the cells correlated with the catalytic efficiency of the PTE variant expressed in each cell. High selectivity between similar molecules (4HB versus pNP), high sensitivity for pNP detection (~2 μM) and agreement of apo- and holo-structures of PobR scaffold with predetermined computational models are other significant results presented in this work.

Jha, Ramesh K.↗