Highly Efficient Mutagenesis of Claviceps purpurea by Using Protoplasts

Claviceps purpurea ATCC 20102, which is aconidial under laboratory conditions, was grown in submerged culture in the presence of mutagens and various nutritional additives. Protoplasts from such cultures were prepared and regenerated on solid medium to obtain colonies from single cell units. Frequencies of auxotrophs and high alkaloid producers were on the order of 1 to 2%. Some of the auxotrophic mutants derived from strain ATCC 20102 were constantly segregating prototrophs. High-alkaloid-producing derivatives showed sclerotia-like morphology and violet-brown pigmentation, in contrast to the parent strain; some of them also showed segregation sectors when grown as giant colonies. Mutagenesis of strain 1029, isolated during this study and having an increased level of alkaloid synthesis and sclerotia-like cell morphology, was done in the same fashion as with the original parent strain, ATCC 20102. Mutants obtained from this strain were all stable with respect to their genotypes. However, a large proportion of colonies derived from regenerated protoplasts, even in the mutagen-free controls, showed a lowered level of alkaloid production and were morphologically more similar to the original wild type, ATCC 20102. The influence of protoplast preparation or regeneration or both on the stability of genes involved in differentiation is discussed.     

玉米幼胚高效再生系统的建立

建立了玉米幼胚高效再生系统.经研究发现,苏玉1号、农大3138、农大108的幼胚培养在含有2,4-D(2 5 mg/L)的IM培养基上后,大多数幼胚能愈伤化并增大,形成基部相连、上部分开的微芽结构;微芽结构在转移到BM培养基上后,形成小植株;进一步转移到RM培养基上,它们长根并形成完整植株.玉米幼胚高效再生植株与下列因素有关玉米基因型、幼胚大小、幼胚长芽至分化时间、6-BA、IBA、Gelrite.不同品种玉米再生能力有显著差异,幼胚大小在1～2mm之间再生能力强,幼胚长芽至分化时间4～6 d最好.激素6-BA浓度在0.5～0.6 mg/L之间有利于微芽形成小植株,IBA浓度在0.6～1 0 mg/L促进生根.Gelrite可代替琼脂粉用于玉米生根.     

Designing a Highly Efficient Refolding System for Alkaline Phosphatase using Combination of Cyclodextrin and Mg<Superscript>2+</Superscript> Ion

Two different folding aids including α-cyclodextrin and Mg²⁺ ions were applied to alkaline phosphatase refolding. The refolding yield depending on concentration of each of the refolding agents reached to 55 and 52% in the presence of 100 mM α-cyclodextrin and/or 5 mM Mg²⁺ ions, respectively. However, the refolding yield, mediated by combination of α-cyclodextrin and Mg²⁺ ions, was more than 96%. Replacement of Mg²⁺ ion with other type of ions which interact with α-cyclodextrin interfere with the function of cyclodextrin resulting in low refolding yields.     

一种高效的单质粒模式四环素诱导表达系统的构建

现有的四环素诱导调控系统基于两个单独的质粒分别表达反式结合蛋白和外源基因.其缺点是在建立转基因定量表达动物模型时,需要制备和维持两个动物品系,再进行杂交才有可能获得双转基因后代,步骤繁琐,难度较大.针对上述缺陷,本研究尝试将反式蛋白rtTA表达框和低背景响应元件Ptight组装到同一个载体上,构建为严谨型单载体模式的诱导表达系统pTRE-Tight-rtTA,并通过两种报告基因的表达对其调控活性进行了研究.含有荧光素酶和绿色荧光蛋白的pTRE-Tight-rtTA-Luc和pTRE-Tight-rtTA-EGFP报告载体分别转染猪肾PK15细胞并经强力霉素处理,均可成功诱导报告基因的定量表达.在等摩尔转染条件下,单载体系统的诱导效率明显高于双载体系统（Dox-1 000 ng,10 倍;Dox-10 000 ng,8 倍）.该诱导型单载体系统的成功构建为外源基因的定量表达提供了新手段,为转基因定量表达动物模型的研究提供了新策略.     

Highly Efficient Knockout of a Squid Pigmentation Gene

1. Download : Download high-res image (229KB)
2. Download : Download full-size image

     

A Novel In Vitro Method for Detecting Undifferentiated Human Pluripotent Stem Cells as Impurities in Cell Therapy Products Using a Highly Efficient Culture System

Innovative applications of cell therapy products (CTPs) derived from human pluripotent stem cells (hPSCs) in regenerative medicine are currently being developed. The presence of residual undifferentiated hPSCs in CTPs is a quality concern associated with tumorigencity. However, no simple in vitro method for direct detection of undifferentiated hPSCs that contaminate CTPs has been developed. Here, we show a novel approach for direct and sensitive detection of a trace amount of undifferentiated human induced pluripotent stem cells (hiPSCs) using a highly efficient amplification method in combination with laminin-521 and Essential 8 medium. Essential 8 medium better facilitated the growth of hiPSCs dissociated into single cells on laminin-521 than in mTeSR1 medium. hiPSCs cultured on laminin-521 in Essential 8 medium were maintained in an undifferentiated state and they maintained the ability to differentiate into various cell types. Essential 8 medium allowed robust hiPSC proliferation plated on laminin-521 at low cell density, whereas mTeSR1 did not enhance the cell growth. The highly efficient culture system using laminin-521 and Essential 8 medium detected hiPSCs spiked into primary human mesenchymal stem cells (hMSCs) or human neurons at the ratio of 0.001%–0.01% as formed colonies. Moreover, this assay method was demonstrated to detect residual undifferentiated hiPSCs in cell preparations during the process of hMSC differentiation from hiPSCs. These results indicate that our highly efficient amplification system using a combination of laminin-521 and Essential 8 medium is able to detect a trace amount of undifferentiated hPSCs contained as impurities in CTPs and would contribute to quality assessment of hPSC-derived CTPs during the manufacturing process.     

Adsorption of Rare Earths(Ⅲ) Using an Efficient Sodium Alginate Hydrogel Cross-Linked with Poly-γ-Glutamate

With the exploitation of rare earth ore, more and more REEs came into groundwater. This was a waste of resources and could be harmful to the organisms. This study aimed to find an efficient adsorption material to mitigate the above issue. Through doping sodium alginate (SA) with poly-γ-glutamate (PGA), an immobilized gel particle material was produced. The composite exhibited excellent capacity for adsorbing rare earth elements (REEs). The amount of La³⁺ adsorbed on the SA-PGA gel particles reached approximately 163.93 mg/g compared to the 81.97 mg/g adsorbed on SA alone. The factors that potentially affected the adsorption efficiency of the SA-PGA composite, including the initial concentration of REEs, the adsorbent dosage, and the pH of the solution, were investigated. 15 types of REEs in single and mixed aqueous solutions were used to explore the selective adsorption of REEs on gel particles. Scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy analyses of the SA and SA-PGA gel beads suggested that the carboxyl groups in the composite might play a key role in the adsorption process and the morphology of SA-PGA changed from the compact structure of SA to a porous structure after doping PGA. The kinetics and thermodynamics of the adsorption of REEs were well fit with the pseudo-second-order equation and the Langmuir adsorption isotherm model, respectively. It appears that SA-PGA is useful for recycling REEs from wastewater.     

A Designed,Highly Efficient Pyrrolysyl-tRNA Synthetase Mutant Binds o-Chlorophenylalanine Using Two Halogen Bonds

As one of the most valuable tools for genetic code expansion, pyrrolysyl-tRNA synthetase (PylRS) is structurally related to phenylalanyl-tRNA synthetase (PheRS). By introducing mutations that mimic ligand interactions in PheRS into PylRS, we designed a PylRS mutant. This mutant, designated as oClFRS, recognizes a number of o-substituted phenylalanines for their genetic incorporation at amber codon. Its efficiency in catalyzing genetic incorporation of o-chlorophenylalanine (o-ClF) is better than that for N^ε-tert-butyloxycarbonyl-lysine catalyzed by PylRS. The crystal structure of oClFRS bound with o-ClF shows that o-ClF binds deeply into a hydrophobic but catalytically inactive pocket in the active site and involves two halogen bonds to achieve strong interactions. The shift of o-ClF to a catalytically active position in the oClFRS active site will be necessary for its activation. This is the first reported aminoacyl-tRNA synthetase that involves two halogen bonds for ligation recognition and might represent an alternative route to develop aminoacyl-tRNA synthetase mutants that are selective for noncanonical amino acids over native amino acids.     

Construction and Characterization of a Highly Efficient Francisella Shuttle Plasmid

Francisella tularensis is a facultative intracellular pathogen that infects a wide variety of mammals and causes tularemia in humans. It is recognized as a potential agent of bioterrorism due to its low infectious dose and multiple routes of transmission. To date, genetic manipulation in Francisella spp. has been limited due to the inefficiency of DNA transformation, the relative lack of useful selective markers, and the lack of stably replicating plasmids. Therefore, the goal of this study was to develop an enhanced shuttle plasmid that could be utilized for a variety of genetic procedures in both Francisella and Escherichia coli. A hybrid plasmid, pFNLTP1, was isolated that was transformed by electroporation at frequencies of >1 × 10⁷ CFU μg of DNA⁻¹ in F. tularensis LVS, Francisella novicida U112, and E. coli DH5α. Furthermore, this plasmid was stably maintained in F. tularensis LVS after passage in the absence of antibiotic selection in vitro and after 3 days of growth in J774A.1 macrophages. Importantly, F. tularensis LVS derivatives carrying pFNLTP1 were unaltered in their growth characteristics in laboratory medium and macrophages compared to wild-type LVS. We also constructed derivatives of pFNLTP1 containing expanded multiple cloning sites or temperature-sensitive mutations that failed to allow plasmid replication in F. tularensis LVS at the nonpermissive temperature. In addition, the utility of pFNLTP1 as a vehicle for gene expression, as well as complementation, was demonstrated. In summary, we describe construction of a Francisella shuttle plasmid that is transformed at high efficiency, is stably maintained, and does not alter the growth of Francisella in macrophages. This new tool should significantly enhance genetic manipulation and characterization of F. tularensis and other Francisella biotypes.     

Generation of a Highly Active Folding Enzyme by Combining a Parvulin-Type Prolyl Isomerase from SurA with an Unrelated Chaperone Domain

Parvulins are small prolyl isomerases and serve as catalytic domains of folding enzymes. SurA (survival protein A) from the periplasm of Escherichia coli consists of an inactive (Par1) and an active (Par2) parvulin domain as well as a chaperone domain. In the absence of the chaperone domain, the folding activity of Par2 is virtually abolished. We created a chimeric protein by inserting the chaperone domain of SlyD, an unrelated folding enzyme from the FKBP family, into a loop of the isolated Par2 domain of SurA. This increased its folding activity 450-fold to a value higher than the activity of SurA, in which Par2 is linked with its natural chaperone domain. In the presence of both the natural and the foreign chaperone domain, the folding activity of Par2 was 1500-fold increased. Related and unrelated chaperone domains thus are similarly efficient in enhancing the folding activity of the prolyl isomerase Par2. A sequence analysis of various chaperone domains suggests that clusters of exposed methionine residues in mobile chain regions might be important for a generic interaction with unfolded protein chains. This binding is highly dynamic to allow frequent transfer of folding protein chains between chaperone and catalytic domains.     

Highly Efficient Base Editing in Viral Genome Based on Bacterial Artificial Chromosome Using a Cas9-Cytidine Deaminase Fused Protein

Viruses evolve rapidly and continuously threaten animal health and economy, posing a great demand for rapid and efficient genome editing technologies to study virulence mechanism and develop effective vaccine. We present a highly efficient viral genome manipulation method using CRISPR-guided cytidine deaminase. We cloned pseudorabies virus genome into bacterial artificial chromosome, and used CRISPR-guided cytidine deaminase to directly convert cytidine(C) to uridine(U) to induce premature stop mutagenesis in viral genes. The editing efficiencies were 100%. Comprehensive bioinformatic analysis revealed that a large number of editable sites exist in pseudorabies virus(PRV) genomes. Notably, in our study viral genome exists as a plasmid in E. coli, suggesting that this method is virus species-independent. This application of base-editing provided an alternative approach to generate mutant virus and might accelerate study on virulence and vaccine development.     

The Salmonella Type III Secretion System Virulence Effector Forms a New Hexameric Chaperone Assembly for Export of Effector/Chaperone Complexes

Bacteria hijack eukaryotic cells by injecting virulence effectors into host cytosol with a type III secretion system (T3SS). Effectors are targeted with their cognate chaperones to hexameric T3SS ATPase at the bacterial membrane''s cytosolic face. In this issue of the Journal of Bacteriology, Roblin et al. (P. Roblin, F. Dewitte, V. Villeret, E. G. Biondi, and C. Bompard, J Bacteriol 197:688–698, 2015, http://dx.doi.org/10.1128/JB.02294-14) show that the T3SS chaperone SigE of Salmonella can form hexameric rings rather than dimers when bound to its cognate effector, SopB, implying a novel multimeric association for chaperone/effector complexes with their ATPase.     

Highly Efficient Perovskite Solar Cell Photocharging of Lithium Ion Battery Using DC–DC Booster

Solar cells become a viable energy source to charge lithium ion batteries. Here a simple and efficient photocharging design approach is demonstrated, where a promising low cost single junction solar cell such as perovskite solar cell or dye sensitized solar cell efficiently charges a Li₄Ti₅O₁₂‐LiCoO₂ Li‐ion cell using a DC–DC voltage boost converter. The converter boosts the low input voltage of a single junction solar cell to charge a lithium ion cell and offers advantages including maximum power point tracking of solar photovoltaics and overvoltage protection for the lithium ion cell. This is the first demonstration of this technology. This approach leads to the highest reported overall efficiency of 9.36% and average storage efficiency of 77.2% at 0.5 C discharge for a perovskite solar cell‐converter charging. The high efficiency for the perovskite solar cell‐converter charging is attributed to maximum power harvesting along with high power conversion efficiency of the perovskite solar cell and low potential polarization between the charge and discharge voltage plateaus for the Li₄Ti₅O₁₂‐LiCoO₂ Li‐ion cell.     

Controllable Perovskite Crystallization via Antisolvent Technique Using Chloride Additives for Highly Efficient Planar Perovskite Solar Cells

The presence of surface and grain boundary defects in organic–inorganic halide perovskite films can be detrimental to both the performance and operational stability of perovskite solar cells (PSCs). Here, the effect of chloride additives is studied on the bulk and surface defects of the mixed cation and halide PSCs. It is found that using an antisolvent technique, the perovskite film is divided into two layers, i.e., a bottom layer with large grains and a thin capping layer with small grains. The addition of formamidinium chloride (FACl) into the precursor solution removes the small‐grained perovskite capping layer and suppresses the formation of bulk and surface defects, providing a perovskite film with enhanced crystallinity and large grain size of over 1 µm. Time‐resolved photoluminescence measurements show longer lifetimes for perovskite films modified by FACl and subsequently passivated by 1‐adamantylamine hydrochloride as compared to the reference sample. Impedance spectroscopy measurements show that these treatments reduce the recombination in the PSCs, leading to a champion device with power conversion efficiency (PCE) of 21.2%, an open circuit voltage of 1152 mV and negligible hysteresis. The Cl treated PSC also shows improved operational stability with only 12% PCE loss after 700 h under continuous illumination.     

乌桕不同外植体高效再生探索

以乌桕的成熟胚、胚乳、叶片和茎段为外植体,建立高效、稳定的组培快繁再生体系,并成功获得其再生苗.结果表明:(1)全胚乳带胚的愈伤组织诱导率达90%,其愈伤组织继续在MS+1.0 mg·L-1 NAA+1.0 mg·L-1 6-BA培养基上培养,不定芽最多达15个/外植体.(2)去胚乳的胚不加调节剂则胚直接萌动成苗,萌动率和成苗率可达100%;去胚乳的胚在MS+0.05 mg·L-1 NAA+0.3 mg·L-1 6-BA最佳培养基中培养,其胚轴处可直接诱导不定芽,最多达6个/外植体.(3)无菌苗叶片在MS+0.5 mg·L-1 NAA+0.5 mg·L-1 6-BA培养基中诱导的有效不定芽数最高达18个/外植体,诱导率达90%.(4)茎段在MS+0.05 mg·L-1 NAA+0.1~0.3 mg·L-1 6-BA培养基上不定芽的诱导率较高(100%),直接诱导的不定芽数最多达17个/外植体.(5)芽苗在1/2MS+0.5 mg·L-1 IBA上生根率达到100%,但根系较细弱,而在MS+1.0 mg·L-1镧稀土中的生根率达100%,且根系粗壮;生根的小苗练苗移栽后温室内成活率为89.2%,移栽到室外沙质土壤中的成活率为68.9%.