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At least 1,279 records · Page 71
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

The Value of Increased HVDC Capacity Between Eastern and Western U.S. Grids: The Interconnections Seam Study

The Interconnections Seam Study examines the potential economic value of increasing electricity transfer between the Eastern and Western Interconnections using high-voltage direct-current (HVDC) transmission and cost-optimizing both generation and transmission resources across the United States, proposing, assessing, justifying, and illustrating a major infrastructure change involving two of the worlds largest power grids. The study conducted a multi-model analysis that used co-optimized generation and transmission expansion planning and production cost modeling. Four transmission designs under eight scenarios were developed and studied to estimate costs and potential benefits. The results show benefit-to-cost ratios that reach as high as 2.5, indicating significant value to increasing the transmission capacity between the interconnections under the cases considered, realized through sharing generation resources and flexibility across regions.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2024

Paternal preconception alcohol consumption increased Angiotensin II‐mediated vasoconstriction in male offspring cerebral arteries via oxidative stress‐AT1R pathway

Abstract Alcohol consumption is popular worldwidely and closely associated with cardiovascular diseases. Influences of paternal preconception alcohol consumption on offspring cerebral arteries are largely unknown. Male rats were randomly given alcohol or water before being mated with alcohol‐naive females to produce alcohol‐ and control‐sired offspring. Middle cerebral artery (MCA) was tested with a Danish Myo Technology wire myograph, patch‐clamp, IONOPTIX, immunofluorescence and quantitative PCR. Alcohol consumption enhanced angiotensin II (AngII)‐mediated constriction in male offspring MCA mainly via AT1R. PD123,319 only augmented AngII‐induced constriction in control offspring. AngII and Bay K8644 induced stronger intracellular calcium transient in vascular smooth muscle cells (VSMCs) from MCA of alcohol offspring. L‐type voltage‐dependent calcium channel (L‐Ca 2+ ) current at baseline and after AngII‐stimulation was higher in VSMCs. Influence of large‐conductance calcium‐activated potassium channel (BK C a ) was lower. Caffeine induced stronger constriction and intracellular calcium release in alcohol offspring. Superoxide anion was higher in alcohol MCA than control. Tempol and thenoyltrifluoroacetone alleviated AngII‐mediated contractions, while inhibition was significantly higher in alcohol group. The mitochondria were swollen in alcohol MCA. Despite lower Kcnma1 and Prkce expression, many genes expressions were higher in alcohol group. Hypoxia induced reactive oxygen species production and increased AT1R expression in control MCA and rat aorta smooth muscle cell line. In conclusion, this study firstly demonstrated paternal preconception alcohol potentiated AngII‐mediated vasoconstriction in offspring MCA via ROS‐AT1R. Alcohol consumption increased intracellular calcium via L‐Ca 2+ channel and endoplasmic reticulum and decreased BK Ca function. The present study provided new information for male reproductive health and developmental origin of cerebrovascular diseases.

Zhang, Ze↗
DOE OSTI2024

Rev1 overexpression accelerates N -methyl- N -nitrosourea (MNU)-induced thymic lymphoma by increasing mutagenesis

Rev1 has two important functions in the translesion synthesis pathway, including dCMP transferase activity, and acts as a scaffolding protein for other polymerases involved in translesion synthesis. However, the role of Rev1 in mutagenesis and tumorigenesis in vivo remains unclear. We previously generated Rev1-overexpressing (Rev1-Tg) mice and reported that they exhibited a significantly increased incidence of intestinal adenoma and thymic lymphoma (TL) after N-methyl-N-nitrosourea (MNU) treatment. In this study, we investigated mutagenesis of MNU-induced TL tumorigenesis in wild-type (WT) and Rev1-Tg mice using diverse approaches, including whole-exome sequencing (WES). In Rev1-Tg TLs, the mutation frequency was higher than that in WT TL in most cases. However, no difference in the number of nonsynonymous mutations in the Catalogue of Somatic Mutations in Cancer (COSMIC) genes was observed, and mutations involved in Notch1 and MAPK signaling were similarly detected in both TLs. Mutational signature analysis of WT and Rev1-Tg TLs revealed cosine similarity with COSMIC mutational SBS5 (aging-related) and SBS11 (alkylation-related). Interestingly, the total number of mutations, but not the genotypes of WT and Rev1-Tg, was positively correlated with the relative contribution of SBS5 in individual TLs, suggesting that genetic instability could be accelerated in Rev1-Tg TLs. Finally, we demonstrated that preleukemic cells could be detected earlier in Rev1-Tg mice than in WT mice, following MNU treatment. In conclusion, Rev1 overexpression accelerates mutagenesis and increases the incidence of MNU-induced TL by shortening the latency period, which may be associated with more frequent DNA damage-induced genetic instability.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Lower soil moisture and deep soil temperatures in thermokarst features increase old soil carbon loss after 10 years of experimental permafrost warming

Almost half of the global terrestrial soil carbon (C) is stored in the northern circumpolar permafrost region, where air temperatures are increasing two times faster than the global average. As climate warms, permafrost thaws and soil organic matter becomes vulnerable to greater microbial decomposition. Long-term soil warming of ice-rich permafrost can result in thermokarst formation that creates variability in environmental conditions. Consequently, plant and microbial proportional contributions to ecosystem respiration may change in response to long-term soil warming. Natural abundance δ 13 C and Δ 14 C of aboveground and belowground plant material, and of young and old soil respiration were used to inform a mixing model to partition the contribution of each source to ecosystem respiration fluxes. We employed a hierarchical Bayesian approach that incorporated gross primary productivity and environmental drivers to constrain source contributions. We found that long-term experimental permafrost warming introduced a soil hydrology component that interacted with temperature to affect old soil C respiration. Old soil C loss was suppressed in plots with warmer deep soil temperatures because they tended to be wetter. When soil volumetric water content significantly decreased in 2018 relative to 2016 and 2017, the dominant respiration sources shifted from plant aboveground and young soil respiration to old soil respiration. The proportion of ecosystem respiration from old soil C accounted for up to 39% of ecosystem respiration and represented a 30-fold increase compared to the wet-year average. Our findings show that thermokarst formation may act to moderate microbial decomposition of old soil C when soil is highly saturated. However, when soil moisture decreases, a higher proportion of old soil C is vulnerable to decomposition and can become a large flux to the atmosphere. Furthermore, as permafrost systems continue to change with climate, we must understand the thresholds that may propel these systems from a C sink to a source.

permafrost↗
DOE OSTI2024

Advances in Miscanthus × Giganteus Planting Techniques May Increase Carbon Uptake in the Establishment Year

Agricultural lands hold significant potential for CO 2 sequestration, particularly when utilizing biomass crops and agricultural residues. Among these, Miscanthus × giganteus (mxg) stands out due to its high productivity and carbon sequestration capabilities. Recognizing the importance of such biomass crops, the Intergovernmental Panel on Climate Change (IPCC) has identified Bioenergy with Carbon Capture and Storage (BECCS) as a crucial strategy for achieving net-zero CO 2 emissions by 2050. This study examines the carbon uptake potential of mxg during its establishment year at the Sustainable Advanced Bioeconomy Research (SABR) farm in Iowa, USA, where mxg was planted at a density exceeding previous studies. Using eddy covariance (EC) measurements, we quantified the net ecosystem carbon exchange (NEE), and derived gross primary productivity (GPP), and ecosystem respiration (R eco ). Our findings reveal that SABR's mxg exhibited a significant carbon uptake of –621 g C m –2 , a threefold increase compared to a similar EC site in the “corn-belt” (University of Illinois Energy Research Farm; UIEF), which was established with lower planting density and pre-commercial planting equipment. Favorable growing conditions and advanced planting technologies at SABR likely contributed to this high carbon uptake. Comparisons with other global EC studies indicated a strong correlation between higher planting densities and greater carbon uptake. These results suggest that increasing mxg planting density can enhance carbon uptake, but further studies are necessary to evaluate the impacts under varying environmental conditions and management practices. Additionally, economic analyses are essential to determine the viability of higher planting densities. Our study underscores the potential of optimized mxg management practices to contribute significantly to CO 2 uptake and supports the development of BECCS as a viable climate change mitigation strategy.

09 BIOMASS FUELS↗
DOE OSTI2017

Proportion of fine roots, but not plant biomass allocation below ground, increases with elevation in arctic tundra

Questions: Roots represent a considerable proportion of biomass, primary production and litter input in arctic tundra, and plant allocation of biomass to above- or below- ground tissue in response to climate change is a key factor in the future C balance of these ecosystems. According to optimality theory plants allocate C to the above- or below-ground structure that captures the most limiting resource. We used an elevational gradient to test this theory and as a space-for-time substitution to inform on tundra carbon allocation patterns under a shifting climate, by exploring if increasing elevation was positively related to the root:shoot ratio, as well as a larger plant allocation to adsorptive over storage roots. Location: Arctic tundra heath dominated by Empetrum hermaphroditum close to Abisko, Sweden. Methods: We measured root:shoot and fine:coarse root ratios of the plant communities along an elevational gradient by sampling above- and below-ground biomass, further separating root biomass into fine (<1 mm) and coarse roots. Results: Plant biomass was higher at the lower elevations, but the root:shoot ratio did not vary with elevation. Resource allocation to fine relative to coarse roots increased with elevation, resulting in a fine:coarse root ratio that more than doubled with in- creasing elevation. Conclusions: Contrary to previous works, the root:shoot ratio along this elevational gradient remained stable. However, communities along our study system were dominated by the same species at each elevation, which suggests that when changes in the root:shoot ratio occur with elevation these changes may be driven by differences in allocation patterns among species and thus turnover in plant community structure. Our results further reveal that the allocation of biomass to fine relative to coarse roots can differ between locations along an elevational gradient, even when overall above- vs below-ground biomass allocation does not. Given the functionally different roles of fine vs coarse roots this could have large implications for below-ground C cycling. Thus. our results highlight the importance of direct effects vs indirect effects (such as changes in plant community composition and nutrient availability) of climate change for future C allocation above and below ground.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Winter warming rapidly increases carbon degradation capacities of fungal communities in tundra soil: Potential consequences on carbon stability

We report high-latitude tundra ecosystems are increasingly affected by climate warming. As an important fraction of soil microorganisms, fungi play essential roles in carbon degradation, especially the old, chemically recalcitrant carbon. However, it remains obscure how fungi respond to climate warming and whether fungi, in turn, affect carbon stability of tundra. In a 2-year winter soil warming experiment of 2°C by snow fences, we investigated responses of fungal communities to warming in the active layer of an Alaskan tundra. Although fungal community composition, revealed by the 28S rRNA gene amplicon sequencing, remained unchanged (p > .05), fungal functional gene composition, revealed by a microarray named GeoChip, was altered (p < .05). Changes in functional gene composition were linked to winter soil temperature, thaw depth, soil moisture, and gross primary productivity (canonical correlation analysis, p < .05). Specifically, relative abundances of fungal genes encoding invertase, xylose reductase and vanillin dehydrogenase significantly increased (p < .05), indicating higher carbon degradation capacities of fungal communities under warming. Accordingly, we detected changes in fungal gene networks under warming, including higher average path distance, lower average clustering coefficient and lower percentage of negative links, indicating that warming potentially changed fungal interactions. Together, our study reveals higher carbon degradation capacities of fungal communities under short-term warming and highlights the potential impacts of fungal communities on tundra ecosystem respiration, and consequently future carbon stability of high-latitude tundra.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2013

Elevated CO2 increases tree-level intrinsic water use efficiency: insights from carbon and oxygen isotope analyses in tree rings across three forest FACE sites

Elevated CO2 increases intrinsic water use efficiency (WUEi) of forests, but the magnitude of this effect and its interaction with climate is still poorly understood. We combined tree ring analysis with isotope measurements at three Free Air CO2 Enrichment (FACE, POP-EUROFACE, in Italy; Duke FACE in North Carolina and ORNL in Tennessee, USA) sites, to cover the entire life of the trees. We used 13C to assess carbon isotope discrimination ( 13C ci/ca) and changes in WUEi, while direct CO2 effects on stomatal conductance were explored using 18O as a proxy. Across all the sites, elevated CO2 increased 13C-derived WUEi on average by 73% for Liquidambar styraciflua, 77% for Pinus taeda and 75% for Populus sp., but through different ecophysiological mechanisms. Our findings provide a robust means of predicting WUEi responses from a variety of tree species exposed to variable environmental conditions over time, and species-specific relationships that can help modeling elevated CO2 and climate impacts on forest productivity, carbon and water balances.

Battipaglia, Giovanna↗
DOE OSTI2018

Salicylic acid activates poplar defense against the biotrophic rust fungus Melampsora larici-populina via increased biosynthesis of catechin and proanthocyanidins

Poplar trees synthesize flavan-3-ols (catechin and proanthocyanidins) as a defense against foliar rust fungi, but the regulation of this defense response is poorly understood. Here, we investigated the role of hormones in regulating flavan-3-ol accumulation in poplar during rust infection. We profiled levels of defense hormones, signaling genes, and flavan-3-ol metabolites in black poplar leaves at different stages of rust infection. Hormone levels were manipulated by external sprays, genetic engineering, and drought to reveal their role in rust fungal defenses. Levels of salicylic acid (SA), jasmonic acid, and abscisic acid increased in rust-infected leaves and activated downstream signaling, with SA levels correlating closely with those of flavan-3-ols. Pretreatment with the SA analog benzothiadiazole increased flavan-3-ol accumulation by activating the MYB–bHLH–WD40 complex and reduced rust proliferation. Furthermore, transgenic poplar lines overproducing SA exhibited higher amounts of flavan-3-ols constitutively via the same transcriptional activation mechanism. These findings suggest a strong association among SA, flavan-3-ol biosynthesis, and rust resistance in poplars. Abscisic acid also promoted poplar defense against rust infection, but likely through stomatal immunity independent of flavan-3-ols. Jasmonic acid did not confer any apparent defense responses to the fungal pathogen. We conclude that SA activates flavan-3-ol biosynthesis in poplar against rust infection.

Plant Sciences↗
DOE OSTI2019

Increased adaxial stomatal density is associated with greater mesophyll surface area exposed to intercellular air spaces and mesophyll conductance in diverse C 4 grasses

Summary Mesophyll conductance ( g m ) is the diffusion of CO 2 from intercellular air spaces ( IAS ) to the first site of carboxylation in the mesophyll cells. In C 3 species, g m is influenced by diverse leaf structural and anatomical traits; however, little is known about traits affecting g m in C 4 species. To address this knowledge gap, we used online oxygen isotope discrimination measurements to estimate g m and microscopy techniques to measure leaf structural and anatomical traits potentially related to g m in 18 C 4 grasses. In this study, g m scaled positively with photosynthesis and intrinsic water‐use efficiency ( TE i ), but not with stomatal conductance. Also, g m was not determined by a single trait but was positively correlated with adaxial stomatal densities ( SD ada ), stomatal ratio ( SR ), mesophyll surface area exposed to IAS ( S mes ) and leaf thickness. However, g m was not related to abaxial stomatal densities ( SD aba ) and mesophyll cell wall thickness ( T CW ). Our study suggests that greater SD ada and SR increased g m by increasing S mes and creating additional parallel pathways for CO 2 diffusion inside mesophyll cells. Thus, SD ada , SR and S mes are important determinants of C 4 ‐ g m and could be the target traits selected or modified for achieving greater g m and TE i in C 4 species.

Pathare, Varsha S.↗
DOE OSTI2021

Flg22‐induced Ca 2+ increases undergo desensitization and resensitization

The flagellin epitope flg22, a pathogen-associated molecular pattern (PAMP), binds to the receptor-like kinase FLAGELLIN SENSING2 (FLS2), and triggers Ca 2+ influx across the plasma membrane (PM). The flg22-induced increases in cytosolic Ca 2+ concentration ([Ca 2+ ]i) (FICA) play a crucial role in plant innate immunity. It's well established that the receptor FLS2 and reactive oxygen species (ROS) burst undergo sensitivity adaptation after flg22 stimulation, referred to as desensitization and resensitization, to prevent over responses to pathogens. However, whether FICA also mount adaptation mechanisms to ensure appropriate and efficient responses against pathogens remains poorly understood. Here, we analysed systematically [Ca 2+ ]i increases upon two successive flg22 treatments, recorded and characterized rapid desensitization but slow resensitization of FICA in Arabidopsis thaliana. Pharmacological analyses showed that the rapid desensitization might be synergistically regulated by ligand-induced FLS2 endocytosis as well as the PM depolarization. The resensitization of FICA might require de novo FLS2 protein synthesis. FICA resensitization appeared significantly slower than FLS2 protein recovery, suggesting additional regulatory mechanisms of other components, such as flg22-related Ca 2+ permeable channels. Taken together, we have carefully defined the FICA sensitivity adaptation, which will facilitate further molecular and genetic dissection of the Ca 2+ -mediated adaptive mechanisms in PAMP-triggered immunity.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Direct current response of a thin scCVD diamond detector under increased applied field to 14.1 MeV neutrons

An avalanche effect yielding inherent gain can be exploited in thin, single-crystal chemical vapor deposition (scCVD) diamond. It occurs when a high enough bias is applied across the diamond thickness while avoiding breakdown. This charge multiplication effect was studied previously with alpha particles and heavy ions either by using the transient current technique or by measuring the energy spectrum. The measurements we obtained to evaluate the charge multiplication performance of a 10 μm thick scCVD diamond detector used a novel approach—we employed an electrometer to characterize the response of the detector by performing directly coupled current measurements (time-averaged charge, at 1 Hz sampling) when exposed to 14.1 MeV neutrons from deuterium-tritium fusion. We measured both the dark and irradiated currents from the detector over a range of applied displacement field values from 2 to 75 V/μm. A histogram method with central mean and standard deviation width was used to determine the current over each measurement duration typically from 100 to 300 seconds. The dark-subtracted irradiated current (i.e., contrast) was used to evaluate the gain of the detector at each applied displacement field. The contrast at an applied displacement field between 15 and 20 V/μm was higher than the expected linear increase in contrast proportional to the increased applied bias, indicating the possible presence of avalanche events in the diamond. The detector response also indicated possible polarization and charge depletion effects. These results provide an opportunity to further explore the use of thin scCVD diamond as a fast neutron current mode detector with inherent gain.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Correcting radiation survey data to account for increased leakage during intensity modulated radiotherapy treatments

Purpose: Intensity modulated radiotherapy (IMRT) treatments require more beam-on time and produce more linac head leakage to deliver similar doses to conventional, unmodulated, radiotherapy treatments. It is necessary to take this increased leakage into account when evaluating the results of radiation surveys around bunkers that are, or will be, used for IMRT. The recommended procedure of applying a monitor-unit based workload correction factor to secondary barrier survey measurements, to account for this increased leakage when evaluating radiation survey measurements around IMRT bunkers, can lead to potentially costly overestimation of the required barrier thickness. This study aims to provide initial guidance on the validity of reducing the value of the correction factor when applied to different radiation barriers (primary barriers, doors, maze walls, and other walls) by evaluating three different bunker designs.Methods: Radiation survey measurements of primary, scattered, and leakage radiation were obtained at each of five survey points around each of three different radiotherapy bunkers and the contribution of leakage to the total measured radiation dose at each point was evaluated. Measurements at each survey point were made with the linac gantry set to 12 equidistant positions from 0° to 330°, to assess the effects of radiation beam direction on the results.Results: For all three bunker designs, less than 0.5% of dose measured at and alongside the primary barriers, less than 25% of the dose measured outside the bunker doors and up to 100% of the dose measured outside other secondary barriers was found to be caused by linac head leakage.Conclusions: Results of this study suggest that IMRT workload corrections are unnecessary, for survey measurements made at and alongside primary barriers. Use of reduced IMRT workload correction factors is recommended when evaluating survey measurements around a bunker door, provided that a subset of the measurements used in this study are repeated for the bunker in question. Reduction of the correction factor for other secondary barrier survey measurements is not recommended unless the contribution from leakage is separately evaluated.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

Sci—Fri AM: Mountain — 04: Label-free Raman spectroscopy of single tumour cells detects early radiation-induced glycogen synthesis associated with increased radiation resistance

Purpose: To use label-free Raman spectroscopy (RS) for early treatment monitoring of tumour cell radioresistance. Methods: Three human tumour cell lines, two radioresistant (H460, SF{sub 2} = 0.57 and MCF7, SF{sub 2} = 0.70) and one radiosensitive (LNCaP, SF{sub 2} = 0.36), were irradiated with single fractions of 2, 4, 6, 8 or 10 Gy. In additional experiments, H460 and MCF7 cells were irradiated under co-treatment with the anti-diabetic drug metformin, a known radiosensitizing agent. Treated and control cultures were analyzed with RS daily for 3 days post-treatment. Single-cell Raman spectra were acquired from 20 live cells per sample, and experiments were repeated in triplicate. The combined data sets were analyzed with principal component analysis using standard algorithms. Cells from each culture were also subjected to standard assays for viability, proliferation, cell cycle, and radiation clonogenic survival. Results: The radioresistant cells (H460, MCF7) exhibited a RS molecular radiation response signature, detectable as early as 1 day post-treatment, of which radiation-induced glycogen synthesis is a significant contributor. The radiosensitive cells (LNCaP) exhibited negligible glycogen synthesis. Co-treatment with metformin in MCF7 cells blocked glycogen synthesis, reduced viability and proliferation, and increased radiosensitivity. Conversely, metformin co-treatment in H460 cells did not produce these same effects; importantly, both radiation-induced synthesis of glycogen and radiosensitivity were unaffected. Conclusions: Label-free RS can detect early glycogen synthesis post-irradiation, a previously undocumented metabolic mechanism associated with tumour cell radioresistance that can be targeted to increase radiosensitivity. RS monitoring of intratumoral glycogen may provide new opportunities for personalized combined modality radiotherapy treatments.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-F-T-131: No Increase in Biological Effectiveness Through Collimator Scattered Low Energy Protons

Purpose: To reduce the lateral penumbra of low-energy proton beams, brass collimators are often used in spot-scanning proton therapy (SSPT). This study investigates the increase in biological effectiveness through collimator scattered protons in SSPT. Methods: The SSPT system of the Hokkaido University Hospital Proton Beam Therapy Center, which consists of a scanning nozzle, a 2-cm thick brass collimator, and a 4-cm thick energy absorber, was simulated with our validated Geant4 Monte Carlo code (ver. 9.3). A water phantom was irradiated with proton pencil beams of 76, 110, and 143 MeV. The tested collimator opening areas (COA) were 5×5, 10×10, and 15×15 cm{sup 2}. Comparisons were made among the dose-averaged LET values of protons that hit the collimators (LETDColl), protons that did not hit the collimators (LETDNoColl), and all protons (LETDTotal). X-ray equivalent doses (Deq) were calculated using the linear-quadratic model with LETDNoColl and LETDTotal, and their maximum difference was determined over regions where the physical dose was greater than 10% of the peak dose of 2 Gy. Results: The ratio of the dose contribution of collimator scattered protons to that of all protons, defined as λ, was large at high proton energies and large COAs. The maximum λ value ranged from 3% (76 MeV, 5×5 cm{sup 2}) to 29% (143 MeV, 15×15 cm{sup 2}). Moreover, a large difference between LETDColl and LETDNoColl was only found in regions where λ was below 20% (ΔLETD > 2 keV/µm) and 8% (ΔLETD > 5 keV/µm). Consequently, the maximum difference between LETDNoColl and LETDTotal was as small as 0.8 keV/µm in all simulated voxels, and the difference of Deq reached a maximum of 1.5% that of the peak dose obtained at the water surface with a 76 MeV beam. Conclusion: Although collimator scattered protons have high LET, they only increase the physical dose, not the biological effectiveness.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2023

Increased U.S. coastal hurricane risk under climate change

Several pathways for how climate change may influence the U.S. coastal hurricane risk have been proposed, but the physical mechanisms and possible connections between various pathways remain unclear. Here, future projections of hurricane activity (1980–2100), downscaled from multiple climate models using a synthetic hurricane model, show an enhanced hurricane frequency for the Gulf and lower East coast regions. The increase in coastal hurricane frequency is driven primarily by changes in steering flow, which can be attributed to the development of an upper-level cyclonic circulation over the western Atlantic. The latter is part of the baroclinic stationary Rossby waves forced mainly by increased diabatic heating in the eastern tropical Pacific, a robust signal across the multimodel ensemble. Last, these heating changes also play a key role in decreasing wind shear near the U.S. coast, further aggravating coastal hurricane risk enhanced by the physically connected steering flow changes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Polyamine Transporters and Polyamines Increase Furfural Tolerance during Xylose Fermentation with Ethanologenic Escherichia coli Strain LY180

Expression of genes encoding polyamine transporters from plasmids and polyamine supplements increased furfural tolerance (growth and ethanol production) in ethanologenic Escherichia coli LY180 (in AM1 mineral salts medium containing xylose). Furthermore, this represents a new approach to increase furfural tolerance and may be useful for other organisms. Microarray comparisons of two furfural-resistant mutants (EMFR9 and EMFR35) provided initial evidence for the importance of polyamine transporters. Each mutant contained a single polyamine transporter gene that was upregulated over 100-fold (microarrays) compared to that in the parent LY180, as well as a mutation that silenced the expression of yqhD. Based on these genetic changes, furfural tolerance was substantially reconstructed in the parent, LY180.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Increasing Growth Yield and Decreasing Acetylation in Escherichia coli by Optimizing the Carbon-to-Magnesium Ratio in Peptide-Based Media

Complex media are routinely used to cultivate diverse bacteria. However, this complexity can obscure the factors that govern cell growth. While studying protein acetylation in buffered tryptone broth supplemented with glucose (TB7-glucose), we observed that Escherichia coli did not fully consume glucose prior to stationary phase. However, when we supplemented this medium with magnesium, the glucose was completely consumed during exponential growth, with concomitant increases in cell number and biomass but reduced cell size. Similar results were observed with other sugars and other peptide-based media, including lysogeny broth. Magnesium also limited cell growth for Vibrio fischeri and Bacillus subtilis in TB7-glucose. Finally, magnesium supplementation reduced protein acetylation. Based on these results, we conclude that growth in peptide-based media is magnesium limited. We further conclude that magnesium supplementation can be used to tune protein acetylation without genetic manipulation. These results have the potential to reduce potentially deleterious acetylated isoforms of recombinant proteins without negatively affecting cell growth. Bacteria are often grown in complex media. These media are thought to provide the nutrients necessary to grow bacteria to high cell densities. In this work, we found that peptide-based media containing a sugar are magnesium limited for bacterial growth. In particular, magnesium supplementation is necessary for the bacteria to use the sugar for cell growth. Interestingly, in the absence of magnesium supplementation, the bacteria still consume the sugar. However, rather than use it for cell growth, the bacteria instead use the sugar to acetylate lysines on proteins. As lysine acetylation may alter the activity of proteins, this work demonstrates how lysine acetylation can be tuned through magnesium supplementation. These findings may be useful for recombinant protein production, when acetylated isoforms are to be avoided. In conclusion, they also demonstrate how to increase bacterial growth in complex media.

59 BASIC BIOLOGICAL SCIENCES↗