Electroporation of Haemophilus influenzae is effective for transformation of plasmid but not chromosomal DNA.

Electroporation of plasmid and chromosomal DNAs were tested in Haemophilus influenzae because of an interest in introducing DNA into mutants that are deficient in competence for transformation. The initial experiments were designed to investigate and optimize conditions for electroporation of H. influenzae. Plasmid DNA was introduced into the competence proficient strain Rd and its competence-deficient uptake mutants com-52, com-59, and com-88, and the recombination deficient mutant rec1. Plasmid DNA could also be electroporated into the non-transforming strains Ra, Rc, Re and Rf. Plasmid DNA without sequences that are involved in tight binding (uptake) of DNA by competent cells of H. influenzae Rd was electroporated into both competent and non-competent cells. Competent cells were several orders of magnitude less efficient than non-competent cells for electroporation of plasmid DNAs. Electroporation of H. influenzae chromosomal DNA was not successful. Low levels of integration of chromosomal markers were observed following electroporation and these could be ascribed to transformation. The treatment of cells with DNasel following electroporation separated the effects due to electroporation from those due to transformation. The DNasel treatment did not affect the efficiency of plasmid incorporation, but severely restricted effects due to natural DNA transformation.     

Properties of electroporation-mediated DNA transfer in Escherichia coli

Efficient and reproducible DNA-transfection was attained in E. coli, by electroporation. The yield of the transfectants was affected by pretreatment of the recipient cells as well as by the composition of the electroporation medium. Using a single pulse procedure, relationships among the electrical parameters, the transfection efficiency, and the cellular viability were investigated in 10 mM Tris-HCl buffer (pH 7.5) containing 5% sucrose. Certain sodium salts (e.g., citrate, phosphate, and sulfate) were promotive, whereas Mg2+, DEAE-dextran, and polyvinylpyrrolidone were inhibitory to the transfection. Heterologous nucleic acids (native DNA, denatured DNA, and tRNA) exerted only a marginal effect on transfection with a viral replicative-form DNA. The efficiency of DNA transfer was affected by culture conditions, and bacteria grown at a higher temperature were more competent. The electroporation system was more efficient than an improved CaCl2 method, not only in transfection with viral single- and double-stranded DNAs, but also in transformation with plasmid DNAs.     

DH10B菌株高效电转化条件探究

以pUC19、pECBAC1、pCLD04541DNA以及3个不同大小的BACDNA为材料,研究了E.coli DH10B菌株在5个不同脉冲电场下的转化效率。研究发现,随着DNA片段大小的增加,最高转化效率和最适场强迅速减小。利用DH10B细胞转化pUC19 DNA的最适场强是21kV/cm,而190kb BAC DNA仅为13kV/cm;在最适场强下,40kb BAC DNA的转化效率约是190kb BAC DNA的50倍。通过大量数据绘制了不同因素影响下转化效率的变化曲线,优化了E.coli DH10B菌株电转化条件,为质粒的重组转化以及大片段基因组文库的构建奠定了基础。     

Atrogin-1/MAFbx,a Muscle-Specific Ubiquitin Ligase,Is Highly Expressed in the Smooth Muscle of the Chicken Gizzard

To improve the transformation efficiency of Zygosaccharomyces rouxii by electroporation, glycerol was added to the electroporation buffer and the cells were frozen at ?80 °C. These alterations drastically increased transformation efficiency, and we found that competent cells can be preserved at ?80 °C without decreasing their transformation efficiency for at least 30 d.     

Analyzing gene regulation in ascidian embryos: new tools for new perspectives

Ascidians are marine protochordates at the evolutionary boundary between invertebrates and vertebrates. Ascidian larvae provide a simple system for unraveling gene regulation networks underlying the formation of the basic chordate body plan. After being used for over a century as a model for embryological studies, ascidians have become, in the past decade, an increasingly popular organism for studying gene regulation. Part of the renewed appeal of this system is the use of electroporation to introduce transgenic DNAs into developing embryos. This method is considerably more efficient than conventional microinjection assays and permits the simultaneous transformation of hundreds of embryos. Electroporation has allowed the identification and characterization of cis-regulatory DNAs that mediate gene expression in a variety of tissues, including the notochord, tail muscles, CNS, and endoderm. Electroporation has also provided a simple method for misexpressing patterning genes and producing dominant mutant phenotypes. Recent studies have used electroporation to create "knock-out" phenotypes by overexpressing dominant negative forms of particular proteins. Here we review the past and present uses of electroporation in ascidian development, and speculate on potential future uses.     

Dictyostelium discoideum transformation by oscillating electric field electroporation

Dictyostelium discoideum has been used as a genetically tractable model organism to study many biological phenomena. High-efficiency transformation is a prerequisite for successful genetic screens such as mutant complementation, identification of suppressor genes, or insertional mutagenesis. Although exponential decay electroporation is the standard transformation technique for D. discoideum, its efficiency is relatively low and its reproducibility is weak. Here we optimized the oscillating electroporation technique for D. discoideum transformation and compared it to the exponential decay electroporation. A 20-fold increase in the efficiency was resproducibly achieved. This alternative electroporation technique should facilitate future genetic approaches in D. discoideum.     

Optimization of electrotransformation conditions for Propionibacterium acnes

Propionibacterium acnes has been known to be involved in the pathology of acne. However, the definite mechanism in the development of acne and the inflammation are unknown. For P. acnes, a transformation method has not been established, although it is believed to be a basic tool for gene manipulation. This study attempted to develop a P. acnes transformation method by using electroporation. Various parameters were used to develop and optimize the transformation of P. acnes. Among them two factors were crucial in the transformation for P. acnes: one was the E. coli strain from which the plasmid DNA had been isolated and the other the growth temperature of P. acnes-competent cells. It was essential to prepare plasmid DNA from a dam(-) E. coli strain, ET12567. When plasmid DNAs isolated from the other E. coli strains such as JM109 and HB101 were tested, transformation efficiency was extremely low. When P. acnes cells were cultivated at 24 degrees C for competent cell preparation, transformation efficiency increased considerably. When plasmid DNA isolated from a dam(-) mutant strain of E. coli was used for transformation of P. acnes which had been grown at 24 degrees C, maximum transformation efficiency of 1.5 x 10(4) transformants per mug of plasmid DNA was obtained at a field strength of 15 kV/cm with a pulse time of 3.2 ms. This is believed to be the first report on the transformation of P. acnes which can be employed for gene manipulations including knock-out of specific genes.     

Use of a transient expression assay for the optimization of direct gene transfer into tobacco mesophyll protoplasts by electroporation

Plasmid DNA was transfected into tobacco mesophyll protoplasts by electroporation. Transfection efficiency was estimated, using a transient expression assay based on the measurement of chloramphenicol transacetylase activity or by scoring colonies expressing resistance to paromomycin, an aminoglycoside related to kanamycin. Under conditions of cell survival superior to 50% after electroporation, transient expression signals and transformation efficiencies were found to be proportional. Factors affecting the efficiency of transformation were studied. A clear-cut optimum voltage (250-300 V/cm) was detected. Among various salts tested, potassium chloride was the best electrolyte. No improvement of electroporation efficiency was obtained by a heat-shock (45 degrees C/5 min) treatment prior to electroporation or by the presence of polyethylene glycol in the electroporation medium. The physiological state of plants used as the protoplast source significantly affected the transfection ability of the resulting protoplasts. These results are discussed and compared to previously published procedures.     

High efficiency transformation by electroporation of <Emphasis Type="Italic">Yarrowia lipolytica</Emphasis>

Yarrowia lipolytica was usually transformed by heat shock, but linearized integrative vectors always resulted in a low transformation efficiency when electroporation was used. To develop a high efficiency integrative transformation method by electroporation of F. lipolytica, we report here that pretreatment of F. lipolytica with 150 mM LiAc for 1 h before electroporation will approximately 30-fold of increase transformation efficiency. A cell concentration of 10¹⁰/ml and instrument settings of 1.5 kV will generate the highest transformation efficiencies. We have developed a procedure to transform F. lipolytica that will be able to yield an efficiency of 2.1 × 10⁴ transformants/ug for integrative linear DNA. With our modifications, the electroporation procedures became a very efficient and reliable tool for F. lipolytica transformation.     

Electroporation at elevated temperatures substantially improves transformation efficiency of slow-growing mycobacteria

Abstract The effect of electroporation temperature, biochemical pretreatment of cells and stage of culture on electroporation efficiency for slow-growing mycobacteria were investigated. The efficiency of transformation into Mycobacterium tuberculosis, Mycobacterium bovis and Mycobacterium intracellulare increased markedly with temperature. In contrast, the efficiency of transformation into Mycobacterium smegmatis , a fast-growing species, was higher at 0°C and decreased with temperature. While stage of culture had little effect, a further increase in efficiency of 2–4-fold was obtained following glycine or ethionamide pretreatment. Electroporation at 37°C has been chosen as a standard condition for slow-growing species as it usually resulted in a transformation efficiency several orders of magnitude higher than that obtained at 0°C.     

变形链球菌电击转化条件的优化研究

目的为增强对变形链球菌的电击转化效率,探索常用的胞壁弱化剂甘氨酸在电击转化中的加入模式。方法以氨苄青霉素抗性的pGL3 basic质粒作为外源DNA,通过电击转化导入变形链球菌参考株UA159内,并在选择性培养基上筛选阳性转化克隆,以优化筛选出最佳的甘氨酸加入浓度与模式,同时比较了不同电击方案转化效率的差异。结果在变形链球菌对数生长期后加入终浓度为10%的甘氨酸可有效地增强电击转化的效率;而不同的电转电压的选择对于转化效率的影响,在本实验中差异未见显著性。结论研究证实了甘氨酸作为胞壁弱化剂可增强对变形链球菌的转化效率,并优化了对变形链球菌的电击转化方案。     

Improved method for electroporation of Staphylococcus aureus

We have developed a significantly improved method for the electroporation of plasmid DNA into Staphylococcus aureus. The highest transformation efficiency achieved with this procedure was 4.0 x 10(8) transformants per microgram of plasmid pSK265 DNA. This represents a 530-fold improvement over the previously reported optimum efficiency of 7.5 x 10(5) transformants per microgram of plasmid DNA after electroporation of S. aureus cells [9]. Identical results were obtained when electrocompetent cells, which had been stored frozen at -80 degrees C, were used. The improved efficiency is due primarily to the use of a modified medium (designated as B2 medium) and secondarily to the use of 0.1-cm cuvettes. Several other plasmids (pI258, pMH109, and pSK270) were also electrotransformed into competent cells using our procedure, and for each plasmid, the transformation efficiency was significantly reduced compared to that observed when pSK265 DNA was used. With respect to plasmid pI258, the transformation efficiency was 3500-fold higher than that reported previously for transformation of this plasmid into S. aureus RN4220 [9]. The optimized electroporation procedure was less successful in transforming other staphylococci. Electrocompetent cells of S. aureus ATCC 29213 and S. epidermidis ATCC 12228 produced 5.5 x 10(5) and 5 x 10(3) transformants per microgram of pSK265 DNA, respectively.     

Transformation of Acidiphilium by electroporation and conjugation.

Two techniques, electroporation and conjugation, have been used to introduce the RK2-based broad-host-range plasmids pRK415 and pLAFR3 into strains of the bacterial genus Acidiphilium. Using electroporation, cells were also transformed with a series of chimeric plasmids constructed by cloning cryptic Acidiphilium plasmids into the Escherichia coli vector pBR328. Various parameters affecting electroporation were investigated. Transformation efficiency varied widely with different recipient strains. Growth at an elevated temperature (37 degrees C) prior to electroporation increased transformation efficiency 10-fold compared with growth at 32 degrees C. For three strains tested, optimum transformation efficiency was obtained with field strengths of 10-15 kV/cm. Transformation efficiency increased linearly with increasing DNA concentration up to 10 micrograms/mL. Transformation efficiencies in these experiments ranged up to 10(4) transformants/micrograms DNA. Mobilization of pRK415 and pLAFR3 from E. coli strain S17.1 into several Acidiphilium strains was achieved following incubation for 3 h on nutrient agar medium (pH 7.0). Conjugation frequencies in the range of 10(-5)-10(-9) per recipient cell were obtained. Conjugation frequency was also dependent on recipient strain.     

Transformation of Staphylococcus epidermidis and other staphylococcal species with plasmid DNA by electroporation

In this paper, the influence of various parameters on plasmid transformation by electroporation of Staphylococcus epidermidis Tü3298 was investigated. Cell growth conditions, various concentrations and forms of plasmid DNA, field strength, pulse duration and media for electroporation and regeneration were tested. In order to obtain optimal transformation efficiency, the cells were incubated for 30 min with DNA before pulsing. With the optimized procedure, other staphylococcal species such as S. aureus, S. staphylolyticus and S. carnosus were transformed with an efficiency up to 3 X 10(5) transformants per micrograms pC194 plasmid DNA.     

Optimization of electroporation for transfection of mammalian cell lines

Electroporation can be a highly efficient method for introducing DNA molecules into cultured cells for transient expression of genes or for permanent genetic modification. However, effective transformation by electroporation requires careful optimization of electric field strength and pulse characteristics. We have used the transient expression of the firefly luciferase gene as a rapid and sensitive indicator of gene expression to describe the effects on transfection efficiency of altering electroporation field strength and shape. Using the luciferase assay, we investigated the correlation of cell viability with optimal transfection efficiency and determined the optimal parameters for a number of phenotypically distinct mammalian cell lines derived from the nervous and immune systems. The efficiency of electroporation under optimal conditions was compared with that obtained using DEAE-dextran or calcium phosphate-mediated transformation. Transfection by electroporation using square wave pulses, as opposed to exponentially decaying pulses, was found to be significantly increased by repetitive pulses. These methods improve the ability to obtain high efficiency gene transfer into many mammalian cell types.     

Genetic Transformation in Helicobacter pylori

Genetic transformation in Helicobacter pylori was investigated by using its chromosomal and plasmid DNAs. Six out of the eight strains exhibited the natural competence for incorporation of H. pylori chromosomal DNA, and all the strains incorporated the donor DNA efficiently by washing and concentrating the cells, with a glycerol solution. The much higher frequency of transformation was obtained in each strain by means of electroporation. Electroporation experiments were also conducted by use of the recombinant DNAs consisting of the H. pylori and Escherichia coli plasmids as the donors, and the occurrence of the homologous recombination was demonstrated between the incoming H. pylori plasmid-derived region and the corresponding region of the originally residing plasmid in H. pylori.     

Improved transformation of Pseudomonas putida KT2440 by electroporation

Summary An electric field-mediated transformation (i.e. electroporation) was performed to determine optimal conditions for P. putida transformation. The effects of culture age, electroporation buffer composition, electric field strength, pulse time constant and DNA concentration on transformation efficiency were examined. When plasmid DNA of 8 to 11 kb in size was used with an electroporation buffer containing 1 mM HEPES (pH 7.0), maximum transformation efficiency of 1.0 × 10⁷ transformants/g DNA was obtained at field strength of 12 kV/cm with pulse time of 2.5 millisecond. A linear increase in the number of transformants was observed as DNA concentration was increased over 4 orders of magnitude. A linear relationship was observed between growth phase and transformation efficiency up to OD₆₀₀ = 2.0. This reliable and simple method should be useful for introduction of plasmid DNA into intact P. putida cells.     

High-efficiency transformation of Bacillus subtilis NB22, an antifungal antibiotic iturin producer,by electroporation

High-voltage electroporation was used to transform Bacillus subtilis NB22, an antifungal antibiotic producer, reaching the efficiency of 10⁷ transformants/μg plasmid DNA. Transformation frequency was dependent on the composition of the electroporation solution, the electrical field strength and the cell concentration. Addition of polyethylene glycol (PEG) and mannitol in the transformation solution was critical for a high efficiency of transformation.     

Plasmid transformation of Bacteroides spp. by electroporation

Transformation of Bacteroides spp. with a variety of plasmid DNAs was accomplished using electroporation. The standard transformation assay system used to deduce the optimal electroporation parameters employed a 50-to 100-fold concentrated cell suspension of mid-logarithmic phase Bacteroides fragilis strain 638 and the 5.4-kb clindamycin resistance (Ccr) vector, pBI191. A variety of electroporation buffers were used successfully in transformation experiments but of these, 1 mM MgCl2 in 10% glycerol was superior. The incorporation of MgCl2 was essential for optimum viability prior to electroporation and for optimum transformation. Transformants were routinely obtained using 5-ms pulses over a range of field strengths from 5 to 12.5 kV/cm, with a maximum of greater than 10(6) micrograms-1 DNA at 12.5 kV/cm. The number of transformants increased linearly with respect to DNA concentration over the range 0.01-2 micrograms tested. Recovery of transformants required an expression period of up to 2.5 h following exposure to the electric field. This period, however, was dependent on the antibiotic resistance marker used for selection of transformants, with a significantly shorter incubation required when chloramphenicol rather than clindamycin was used in the selective medium. The effect of the DNA source on transformation was tested using the shuttle vector pFD288. Plasmid DNA isolated from Bacteroides uniformis, Bacteroides ovatus, or Bacteroides thetaiotaomicron transformed B. fragilis 638 at frequencies 7.5- to 12.5-fold less than those observed for controls with homologous DNA. Further reductions were seen with Escherichia coli purified pFD288, which transformed at 1000-fold lower frequencies. Finally, using homologous pFD288 or pBI191 isolated from strain 638, several strains of B. fragilis, B. uniformis, and B. ovatus were transformed successfully without modification of the standard assay system. Two strains each of B. thetaiotaomicron and Bacteroides ruminicola were not transformed using the methods described here.     

A mutagenesis-based screen to rapidly identify phosphorylation sites in mitogen-activated protein kinase substrates

Electroporation is an important approach for genetic engineering experiments allowing for introduction of foreign DNA in a selected host. Here, we describe for the first time the use of glycine betaine as an osmoprotectant for electroporation of gram-positive bacteria Bacillus subtilis. High electroporation efficiency (up to 5×10(5) cfu/μg) was obtained using 7.5% glycine betaine. The new method improved the transformation efficiency of B. subtilis with linear integrative DNA nearly 700-fold compared with existing Bacillus transformation techniques.