YaliCMulti and YaliHMulti: Stable, efficient multi-copy integration tools for engineering Yarrowia lipolytica.

Yarrowia lipolytica is widely used in biotechnology to produce recombinant proteins, food ingredients and diverse natural products. However, unstable expression of plasmids, difficult and time-consuming integration of single and low-copy-number plasmids hampers the construction of efficient production pathways and application to industrial production. Here, by exploiting sequence diversity in the long terminal repeats (LTRs) of retrotransposons and ribosomal DNA (rDNA) sequences, a set of vectors and methods that can recycle multiple and high-copy-number plasmids was developed that can achieve stable integration of long-pathway genes in Y. lipolytica. By combining these sequences, amino acids and antibiotic tags with the Cre-LoxP system, a series of multi-copy site integration recyclable vectors were constructed and assessed using the green fluorescent protein (HrGFP) reporter system. Furthermore, by combining the consensus sequence with the vector backbone of a rapidly degrading selective marker and a weak promoter, multiple integrated high-copy-number vectors were obtained and high levels of stable HrGFP expression were achieved. To validate the universality of the tools, simple integration of essential biosynthesis modules was explored, and 7.3 g/L of L-ergothioneine and 8.3 g/L of (2S)-naringenin were achieved in a 5 L fermenter, the highest titres reported to date for Y. lipolytica. These novel multi-copy genome integration strategies provide convenient and effective tools for further metabolic engineering of Y. lipolytica.

A universal and accurate LPMI method for calculating mismatch in heterogeneous ice nucleation.

The interfacial correlation factor f(m,x), where m refers to the interaction among ice, water and the substrate and x refers to the ratio of the critical nucleation size to the surface topography characteristic size of the substrate, plays a crucial role in the classical theory of heterogeneous ice nucleation as it significantly impacts the energy of nucleation. Generally, a smaller value of f(m,x) indicates a higher propensity for ice nucleation. The degree of structural compatibility between ice and the substrate greatly influences f(m,x), particularly on specific substrates. Several approaches have been proposed to calculate the lattice matching based on this idea, which allows whether a surface is favorable for nucleation to be determined. However, none of these methods adequately correlates the mismatch index with ice growth phenomena. In this paper, we embarked on a new attempt to calculate the mismatch index by combining the lattice parameter and Miller index (LPMI). Droplet freezing experiments have been carried out on α-Al2O3 and silicon surfaces with different Miller indices to verify the rationality of the LPMI method. Furthermore, we validated the LPMI method extensively against other works and further demonstrated its readiness, accuracy and universality for freezing problems. The results consistently show that δd = 2|di - ds|/(di + ds) with interplanar spacing more accurately predicts heterogeneous ice nucleation rates across a wide range of substrates than δ1 = (ai - as)/ai with the lattice parameter of ice and the substrate and is more generally applicable than δ2D = (di - di)/di with the distances between two adjacent and congener atoms on the same plane. We believe that the proposed approach will aid in the selection of substrates for promoting or inhibiting heterogeneous nucleation on a specific substrate.

Potential use of yeast protein in terms of biorefinery, functionality, and sustainability in food industry.

A growing demand for sustainable, alternative protein sources that are nutrient-dense, such as microorganisms, and insects, has gradually evolved. When paired with effective processing techniques, yeast cells contain substantial substances that could supply the population's needs for food, medicine, and fuel. This review article explores the potential of yeast proteins as a sustainable and viable alternative to animal and plant-based protein sources. It highlights the various yeast protein extraction methods including both mechanical and non-mechanical methods. The application of nanoparticles is one example of the fast-evolving technology used to damage microbial cells. SiO2 or Al2O3 nanoparticles break yeast cell walls and disrupt membranes, releasing intracellular bioactive compounds. Succinylation of yeast protein during extraction can increase yeast protein extraction rate, lower RNA concentration, raise yeast protein solubility, increase amino acid content, and improve yeast protein emulsification and foaming capabilities. Combining physical and enzymatic extraction methods generates the most representative pool of mannose proteins from yeast cell walls. Ethanol or isoelectric precipitation purifies mannose proteins. Mannoproteins can be used as foamy replacement for animal-derived components like egg whites due to their emulsification, stability, and foaming capabilities. Yeast bioactive peptide was separated by ultrafiltration after enzymatic hydrolysis of yeast protein and has shown hypoglycemic, hypotensive, and oxidative action in vitro studies. Additionally, the review delves into the physicochemical properties and stability of yeast-derived peptides as well as their applications in the food industry. The article infers that yeast proteins are among the promising sources of sustainable protein, with a wide range of potential applications in the food industry.

Prevalence of symptoms in children with acute lymphoblastic leukaemia: a systematic review and meta-analysis.

BACKGROUND: Children with acute lymphoblastic leukaemia (ALL) experience multiple symptoms that occur in complicated patterns and negatively affect patient outcomes. To date, no systematic review has been performed on the prevalence of symptoms in children with ALL. OBJECTIVE: The study aimed to report and analyse the prevalence of symptoms in children with ALL during treatment. METHODS: A systematic search was conducted in eight databases (PubMed, Ovid Embase, Web of Science, CINAHL, PsycINFO, China WanFang Database, China Science and Technology Journal Database, and China National Knowledge Infrastructure) for studies published between January 1, 2000, and August 12, 2023. The methodological quality of the included studies was evaluated and a meta-analysis was performed to pool the prevalence of symptoms. RESULTS: In total, 17 studies were included, from which 34 symptoms were identified. The symptom prevalence ranged between 1.5 and 91.0% and the most frequent symptoms observed were fatigue, lack of energy, dry mouth, lack of appetite, sweating, and feeling irritable, which occurred in at least 60% of the patients. CONCLUSIONS: Symptoms remain highly prevalent in paediatric patients with ALL, which provides support for the need for symptom assessment in the clinical setting. Specific intervention is urgently needed to mitigate the symptoms in children with ALL and help them cope with the symptom burden.

Assessment of Land Cover Status and Change in the World and "the Belt and Road" Region from 2016 to 2020.

The assessment of land cover and changes will help to understand the temporal and spatial pattern of land cover in the world and the Belt and Road (B&R) region, and provide reference information for global sustainable development and the Belt and Road construction. In this paper, the 1 km global land cover classification maps of 2016 and 2020 with a high accuracy of 88% are mapped using the Moderate Resolution Imaging Spectroradiometer (MODIS) time series surface reflectance products. Based on the maps, the land cover status of the world and the Belt and Road region, the land cover change from 2016 to 2020, and the mutual transformation characteristics between various types, are analyzed. The research results indicate that from 2016 to 2020, the global change rates of cropland, forest, grassland, and impervious surface are 0.25%, 0.22%, 0.08% and 3.41%, respectively. In the Belt and Road region, the change rates of cropland, forest, grassland, and impervious surface are 0.42%, 0.60%, -0.55% and 2.98% respectively. The assessment results will help to clarify the spatial pattern of land cover change in the five years from 2016 to 2020, so as to provide valuable scientific information for the global realization of sustainable development goals and the construction of the B&R.

A sample-to-answer DNA detection microfluidic system integrating sample pretreatment and smartphone-readable gradient plasmonic photothermal continuous-flow PCR.

As the gold standard for nucleic acid detection, full-process polymerase chain reaction (PCR) analysis often falls into the dilemma of complex workflow, time-consuming, and high equipment costs. Therefore, we designed and optimized a DNA quantification microfluidic system by strategically integrating sample pretreatment and a smartphone-readable gradient plasmonic photothermal (GPPT) continuous-flow PCR (CF-PCR). Through preloading and sequential injection of immiscible extraction reagents, combined with magnetic bead (MB) manipulation, the microfluidic chip successfully purified and concentrated 100 µL of HBV-DNA spiked plasma into a 20-µL purified sample within 14 minutes. With a digital PCR platform, the optimized experiments showed that the DNA extraction efficiency can reach 69% at an immiscible reagent configuration ratio of 10 : 10 : 1 : 12 : 2 (sample : lysis/binding buffer : MB : silicone oil : eluent) and a flow rate of 25 µL min-1. For the first time, we used gold nanorod (AuNR)-doped PDMS to prepare a CF-PCR submodule for the amplification of a 40 µL PCR mixture. Due to the plasmonic photothermal effect of AuNRs and the gradient intensity of an expanded laser spot, the PCR thermal gradient was formed on a coin-sized area. The compact annular thermal-microfluidic layout, optimized DNA dye concentration, and chip transmittance synergistically enable a rarely reported smartphone-based fluorescence CF-PCR, greatly simplifying thermal control and detection setup. Prototype construction and validation experiments show that the microsystem can complete the sample-to-answer quantification of HBV-DNA with a dynamic linear range from 1.2 × 101 to 1.2 × 106 copies per µL in ∼37 minutes. This novel microfluidic solution effectively bridges the technical gap between the CF-PCR, sample pretreatment and result characterization, making the workflow standardized and rapid and requiring <15% of the commercial instrument cost. The simplicity, rapidity and low cost of this work make it promising for applications in decentralized laboratories and low-resource settings.

Tomographic Absorption Spectroscopy for H2O Transport in a Laminar Jet with Inverse Concentration Gradient.

We report a tomographic absorption spectroscopy (TAS) study of water vapor transport in a laminar jet issuing into the ambient. The jet was generated using compressed dry air that was straightened by a honeycomb and a smooth contraction nozzle. A TAS scheme using the water vapor in the ambient as absorbing species and the absorption line near 1368.598 nm was proposed to study the H2O transport in the laminar jet with an inverse concentration gradient. One-dimensional tomography was conducted at various heights above the nozzle, and the results were validated by the predictions from computational fluid dynamics (CFD) simulations. Particularly, the variations in the concentration gradient in the shear layer at different heights were captured. The 2D distribution of water concentration in the dry laminar jet was obtained experimentally. The present study shows that TAS has great potential in the research of mass transfer and scalar field of gaseous flows.

Applied evolution: Dual dynamic regulations-based approaches in engineering intracellular malonyl-CoA availability.

Malonyl-CoA is an important building block for microbial synthesis of numerous pharmaceutically interesting or fatty acid-derived compounds including polyketides, flavonoids, phenylpropanoids and fatty acids. However, the tightly regulated intracellular malonyl-CoA availability often impedes overall product formation. Here, in order to unleash this tightly cellular behavior, we present evolution: dual dynamic regulations-based approaches to write artificial robust and dynamic function into intricate cellular background. Firstly, a conserved core domain based evolutionary principles were incorporated into genome mining to explore the biosynthetic diversities of discrete acetyl-CoA carboxylase (ACC) families, as malonyl-CoA is solely derived from carboxylation of acetyl-CoA by ACC in most organisms. A comprehensive phylogenomic and further experimental analysis, which included genomes of 50 strains throughout representative species, was performed to recapitulate the evolutionary history and reveal that previously unnoticed ACC families from Salmonella enterica exhibited the highest activities among all the candidates. A set of orthogonal and bi-functional quorum-sensing (QS)-based regulation tools were further designed and connected with T7 RNA polymerase as genetic amplifier to achieve dual dynamic control in a high dynamic range, which allowed us to efficiently activate and repress different sets of genes dynamically and independently. These genetic circuits were then combined with ACC of S. enterica and CRISPRi system to reprogram central metabolism that rewired the tightly regulated malonyl-CoA pathway to a robust and autonomous behavior, leading to a 29-fold increase of malony-CoA availability. We applied this dual regulation tool to successfully synthesizing malonyl-CoA-derived compound (2S)-naringenin, and achieved the highest production (1073.8 mg/L) reported to date associate with dramatic decreases of by-product formation. Notably, the whole fermentation presents as an autonomous behavior, totally eliminating human supervision and inducer supplementation. Hence, the constructed evolution: dual dynamic regulations-based approaches pave the way to develop an economically viable and scalable procedure for microbial production of malonyl-CoA derived compounds.

Massive droplet generation for digital PCR via a smart step emulsification chip integrated in a reaction tube.

Step emulsification (SE) devices coupled with parallel generation nozzles are widely used in the production of large-scale monodisperse droplets, especially for droplet-based digital polymerase chain reaction (ddPCR) analysis. Although current ddPCR systems based on the SE method can provide a fully enclosed ddPCR scheme, high demands on chip fabrication and system control will increase testing costs and reduce its flexibility in ddPCR analysis. In this study, a compact SE device, integrating a smart SE chip into a reaction tube, was developed to prepare large-scale water-in-fluorinated-oil droplets for ddPCR analysis. The SE chip contained dozens of droplet-generation nozzles. By adjusting the nozzle height of the SE chip, monodisperse droplets in a picolitre to nanolitre vloume could be prepared at a production rate of tens to hundreds of microlitres per minute. Subsequently, we utilized such an integrated SE device to prepare monodisperse droplets for ddPCR experiments. The volume of PCR reagent and the number of droplets could be flexibly adjusted according to the requirements of the ddPCR analysis. The quantitative results showed that emulsions prepared by the SE device could achieve ddPCR detection with high accuracy, good repeatability, and an adaptive dynamic range, which also demonstrated the robustness and reliability of such devices in the droplet preparation. Thus, this compact SE device provides an inexpensive, flexible, and simplified droplet preparation method for digital PCR quantitative analysis.

Performance analysis of a photonic crystal fiber polarization filter filled with different materials.

A compact square photonic crystal fiber polarization filter with high performance is proposed. Two larger holes filled with different metal and fluid are designed to break the strict structure symmetry and forming high birefringence. Four small pores are designed to provide a wider channel for the coupling between defect mode and core mode. Its filtering and coupling characteristics are analyzed by the full vector finite element method. In addition, the properties of PCF filled with different materials are compared and discussed. Different metal materials have different dielectric constants, different optical damping, interband transitions, molecular structure, and physicochemical properties, which make their transmission modes and coupling strength different. The results show that the performance of a PCF filter filled with gold and liquid is the best, which is very suitable for an adjustable PCF polarization filter. The calculation results show that the extinction ratio of the designed filter can reach 5383 dB for a device length of 3 mm; the unwanted fiber loss can reach 2073 dB/cm; and the applicable bandwidth of 2000 nm covers almost the whole communication band. The proposed polarization filter shows large unwanted loss, high extinction ratio, wide bandwidth and coordination, which make it a good candidate for excellent optical fiber filter devices.

Radiometric Performance Evaluation of FY-4A/AGRI Based on Aqua/MODIS.

Fengyun-4A (FY-4A) is the first satellite of the Chinese second-generation geostationary orbit meteorological satellites (FY-4). The Advanced Geostationary Radiation Imager (AGRI), onboard FY-4A does not load with high-precision calibration facility in visible and near infrared (VNIR) channel. As a consequence, it is necessary to comprehensively evaluate its radiometric performance and quantitatively describe the attenuation while using its VNIR data. In this paper, the radiometric performance at VNIR channels of FY-4A/AGRI is evaluated based on Aqua/MODIS data using the deep convective cloud (DCC) target. In order to reduce the influence of view angle and spectral response difference, the bi-directional reflectance distribution function (BRDF) correction and spectral matching have been performed. The evaluation result shows the radiometric performance of FY-4A/AGRI: (1) is less stable and with obvious fluctuations; (2) has a lower radiation level because of 24.99% lower compared with Aqua/MODIS; 3) has a high attenuation with 9.11% total attenuation over 2 years and 4.0% average annual attenuation rate. After the evaluation, relative radiometric normalization between AGRI and MODIS in VNIR channel is performed and the procedure is proved effective. This paper proposed a more reliable reference for the quantitative applications of FY-4A data.

Region-Enhancing Network for Semantic Segmentation of Remote-Sensing Imagery.

Semantic segmentation for high-resolution remote-sensing imagery (HRRSI) has become increasingly popular in machine vision in recent years. Most of the state-of-the-art methods for semantic segmentation of HRRSI usually emphasize the strong learning ability of deep convolutional neural network to model the contextual relationship in the image, which takes too much consideration on every pixel in images and subsequently causes the problem of overlearning. Annotation errors and easily confused features can also lead to the confusion problem while using the pixel-based methods. Therefore, we propose a new semantic segmentation network-the region-enhancing network (RE-Net)-to emphasize the regional information instead of pixels to solve the above problems. RE-Net introduces the regional information into the base network, to enhance the regional integrity of images and thus reduce misclassification. Specifically, the regional context learning procedure (RCLP) can learn the context relationship from the perspective of regions. The region correcting procedure (RCP) uses the pixel aggregation feature to recalibrate the pixel features in each region. In addition, another simple intra-network multi-scale attention module is introduced to select features at different scales by the size of the region. A large number of comparative experiments on four different public datasets demonstrate that the proposed RE-Net performs better than most of the state-of-the-art ones.

Agonists and inhibitors of the STING pathway: Potential agents for immunotherapy.

Since being discovered in 2008, the STING (stimulator of interferon genes) pathway has gradually been recognized as a central and promising target for immunotherapy. The STING pathway can be stimulated by cyclic dinucleotides (CDNs), leading to the type I interferons (IFN) production for immunotherapy for cancer or other diseases. However, the negative charges, hydrophilicity, and instability of CDNs have hindered their further applications. In addition, chronic activation of the STING pathway has been found to be involved in autoimmune diseases as IFN overproduction. Thus, research and development of STING agonists and inhibitors has been a hot field for the treatment of several diseases. The past several years, especially 2018, has seen increasingly rapid advances in this field. Here, this review summarizes the synthesis and modification of CDNs, the identification of nonnucleotide agonists, the recent progress in delivery systems and the medical applications, such as personalized vaccine adjuvants, in detail. In addition, in this review, we summarize the STING inhibitors' advances from two aspects, covalent, and noncovalent inhibitors.

Regulation of Immune Activation by Optical Control of TLR1/2 Heterodimerization.

The activation of toll-like receptors (TLRs) plays important roles in the immune response. The ability to control the activities of TLRs could be usable as a switch for immune response. Here we have rationally designed and synthesized a photoswitchable Pam3 CSK4 derivative-P10-to control the activation of TLR1/2. The ground-state trans-P10 was able to stimulate and activate antigen-presenting cells (APCs) by promoting TLR1/2 heterodimerization. However, cis-P10, derived from UV irradiation of trans-P10, reduced the activities of APCs by impeding the TLR1/2 heterodimerization. In the absence of UV radiation, the cis-P10 slowly returned to its ground trans state, restoring the activities of the APCs stimulation. Our results indicated that optical control of TLR1/2 heterodimerization mediated by the photoswitchable P10 offers the potential to regulate immune activation and inflammation.

Gastrointestinal mixed adenoneuroendocrine carcinoma: a population level analysis of epidemiological trends.

BACKGROUND: The rise in incidence and mortality of gastrointestinal mixed adenoneuroendocrine carcinoma (MANEC) has not been well focused. The aim of our study was to examine epidemiological trends in incidence and incidence-based (IB) mortality of gastrointestinal MANEC at a population level. METHODS: The incidence and IB mortality of gastrointestinal MANEC as well as data on affected patients from 2000 to 2016 were obtained from the Surveillance, Epidemiology, and End Results database. Trends in incidence and IB mortality were assessed using Joinpoint regression. The Kaplan-Meier method and log-rank test were used for survival analysis. Cox proportional hazards regression was used to identify independent predictors of mortality. RESULTS: 581 patients diagnosed with gastrointestinal MANEC were enrolled. Gastrointestinal MANEC incidence was 0.23 cases per 1,000,000 individuals in 2000 and 1.16 cases per 1,000,000 individuals in 2016, with an annual percent change (APC) of 8.0% (95% CI 5.7-10.3%, P < 0.05). IB mortality also showed a sustained increase (APC 12.9%, 95% CI 9.0-16.8%, P < 0.05). In Cox regression analysis, age at diagnosis, tumor grade and stage, lymph node metastasis, surgery, and tumor size were independently associated with mortality. Median survival was 75 months (95% CI 60-128 months). Median survival of appendiceal MANEC was significantly longer than that of cecal MANEC (115 vs. 31 months; P < 0.001). CONCLUSIONS: We found a sustained and rapid increase both in incidence and IB mortality of gastrointestinal MANEC, manifesting that there has been no significant improvement in patient outcomes, nor progress in prevention and treatment. Additional resources should be devoted to gastrointestinal MANEC research.

Pam3CSK4-CDGSF Augments Antitumor Immunotherapy by Synergistically Activating TLR1/2 and STING.

Cyclic dinucleotides (CDNs), agonists of stimulator of interferon genes (STING), are promising agents for immunotherapy. However, the application of CDNs has been limited by their instability and low transmembrane efficiency. Here, we introduced a conjugated adjuvant of STING and TLR1/2, Pam3CSK4-CDGSF. Conjugating CDGSF with Pam3CSK4 increased the stability and intracellular delivery. In addition, by synergistically activating the STING and TLR pathways, Pam3CSK4-CDGSF was able to enhance immune activation. Both humoral and cellular immune responses were triggered by Pam3CSK4-CDGSF plus OVA (V4), and tumor growth was significantly inhibited after V4 administration. More importantly, V4 can also boost the antigen-specific CD8+ T cell response for cancer cell killing. Thus, the conjugated STING and TLR1/2 agonist Pam3CSK4-CDGSF can serve as a potent adjuvant for vaccine construction to augment antitumor immunotherapy.

Asymmetric response of soil methane uptake rate to land degradation and restoration: Data synthesis.

Land degradation and restoration profoundly affect soil CH4 uptake capacity in terrestrial ecosystems. However, a comprehensive assessment of the response of soil CH4 uptake to land degradation and restoration at global scale is not available. Here, we present a global meta-analysis with a database of 228 observations from 83 studies to investigate the effects of land degradation and restoration on the capacity of soil CH4 uptake. We found that land degradation significantly decreased the capacity of soil CH4 uptake, except the conversion of pasture to cropland where the soil CH4 uptake rate showed no response. In contrast, all types of land restoration significantly increased the capacity of soil CH4 uptake. Interestingly, the response of soil CH4 uptake rate to land degradation and restoration was asymmetric: the increased soil CH4 uptake rate in response to the land restoration was smaller compared to the decrease in CH4 uptake rate induced by the land degradation. The effect of land degradation on soil CH4 uptake rate was not dependent on the time since land use change, but the CH4 sink strength increased with the time since land restoration. The response of soil CH4 uptake rate to both land degradation and restoration was predominantly regulated by changes in the soil water-filled pore space, soil bulk density, and pH, whereas alterations in the substrate quantity and quality had negligible effect. Additionally, the effects of land degradation and restoration on soil CH4 uptake were strongly related to the mean annual precipitation and soil texture. Overall, our results provide novel insights for understanding of how land degradation and restoration can affect the CH4 sink strength of upland soils, and more importantly, our findings are beneficial to take measures to enhance the potential of soil CH4 uptake in response to global land use change.

Fully Synthetic Invariant NKT Cell-Dependent Self-Adjuvanting Antitumor Vaccines Eliciting Potent Immune Response in Mice.

Constructing an effective therapeutic cancer vaccine is very attractive and promising for cancer immunotherapy. However, the poor immunogenicity of tumor antigens and suppression of the immune system in the tumor microenvironment are two major obstacles for developing effective cancer vaccines. Invariant NKT cells (iNKT cells), which are essential bridges between the innate and adaptive immune systems, can be rapidly activated by their agonists and, consequently, evoke whole immune systems. Herein, we conjugated a potent agonist of the iNKT cell, α-galactosylceramide (α-GalCer), with the tumor-associated MUC1 glycopeptide antigens as novel self-adjuvanting cancer vaccines through click chemistry. Immunological studies revealed that the mouse immune system was potently evoked and that high levels of tumor-specific IgG antibodies were elicited by vaccine conjugates without an external adjuvant. The produced antibodies could specifically recognize and bind to antigen-expressing cancer cells and, subsequently, induce cytotoxicity through complement-dependent cytotoxicity. Thus, the insertion of α-GalCer significantly improved the immunogenicity of the MUC1 glycopeptide and induced strong antigen-specific antitumor responses, indicating that α-GalCer is an effective built-in adjuvant for constructing potent chemical synthetic antitumor vaccines.

Improving L-serine formation by Escherichia coli by reduced uptake of produced L-serine.

BACKGROUND: Microbial de novo production of L-serine, which is widely used in a range of cosmetic and pharmaceutical products, has attracted increasing attention due to its environmentally friendly characteristics. Previous pioneering work mainly focused on L-serine anabolism; however, in this study, it was found that L-serine could be reimported through the L-serine uptake system, thus hampering L-serine production. RESULT: To address this challenge, engineering via deletion of four genes, namely, sdaC, cycA, sstT and tdcC, which have been reported to be involved in L-serine uptake in Escherichia coli, was first carried out in the L-serine producer E. coli ES. Additionally, the effects of these genes on L-serine uptake activity and L-serine production were investigated. The data revealed an abnormal phenomenon regarding serine uptake activity. The serine uptake activity of the ΔsdaC mutant was 0.798 nmol min-1 (mg dry weight) -1 after 30 min, decreasing by 23.34% compared to that of the control strain. However, the serine uptake activity of the single sstT, cycA and tdcC mutants increased by 34.29%, 78.29% and 48.03%, respectively, compared to that of the control strain. This finding may be the result of the increased level of sdaC expression in these mutants. In addition, multigene-deletion strains were constructed based on an sdaC knockout mutant. The ΔsdaCΔsstTΔtdcC mutant strain exhibited 0.253 nmol min-1 (mg dry weight) -1L-serine uptake activity and the highest production titer of 445 mg/L in shake flask fermentation, which was more than three-fold the 129 mg/L production observed for the parent. Furthermore, the ΔsdaCΔsstTΔtdcC mutant accumulated 34.8 g/L L-serine with a yield of 32% from glucose in a 5-L fermenter after 36 h. CONCLUSION: The results indicated that reuptake of L-serine impairs its production and that an engineered cell with reduced uptake can address this problem and improve the production of L-serine in E. coli.

Water Catalysis of the Reaction of Methanol with OH Radical in the Atmosphere is Negligible.

Faced with the contradictory results of two recent experimental studies [Jara-Toro et al., Angew. Chem. Int. Ed. 2017, 56, 2166 and Chao et al., Angew. Chem. Int. Ed. 2019, 58, 5013] of the possible catalytic effect of water vapor on CH3 OH + OH reaction, we report calculations that corroborate the conclusion made by Chao et al. and extend the rate constant evaluation down to 200 K. The rate constants of the CH3 OH + OH reaction catalyzed by a water molecule are computed as functions of temperature and relative humidity using high-level electronic structure and kinetics calculations. The Wuhan-Minnesota Scaling (WMS) method is used to provide accurate energetics to benchmark a density functional for direct dynamics. Both high-frequency and low-frequency anharmonicities are included. Variational and tunneling effects are treated by canonical variational transition state theory with multidimensional small-curvature tunneling. And, most significantly, we include multistructural effects in the rate constant calculations. Our calculations show that the catalytic effect of water vapor is not observable at 200-400 K.