Genetic Cassette for the TEM-1 β-Lactamase That Improves Plasmid Performance

The genetic cassette encoding the TEM-1 β-lactamase (denoted Tn3.1) is one of the most commonly used and can be found in more than 120 commercially available bacterial expression plasmids (e.g., the pETpUCpGEMpQEpGEXpBAD, and pSEVA series). A widely acknowledged problem with the cassette is that it produces excessively high titers of β-lactamase that rapidly degrade β-lactam antibiotics in the culture media, leading to loss of selective pressure, and eventually a large percentage of cells that do not have a plasmid.

To address these shortcomings, we have engineered a next-generation version that expresses minimal levels of β-lactamase (denoted Tn3.1MIN). We have also engineered a version that is compatible with the Standard European Vector Architecture (SEVA). Expression plasmids containing either Tn3.1MIN or Ap (pSEVA#1MIN–) can be selected using a 5-fold lower concentration of β-lactam antibiotics and benefit from the increased half-life joplink Human ADAD2 cDNA of the β-lactam antibiotics in the culture medium (3- to 10-fold). Moreover, more cells in the culture retain the plasmid.

In summary, we present two antibiotic-efficient genetic cassettes encoding the TEM-1 β-lactamase that reduce antibiotic consumption (an integral part of antibiotic stewardship), reduce production costs, and improve plasmid performance in bacterial cell factories.

Development of TaqMan Real-Time Polymerase Chain Reaction Assay for Detection of Chicken Anemia Virus in Newcastle Disease Vaccines

Exogenous chicken anemia virus (CAV) has been detected in commercial poultry vaccines in various countries of the world. The presence of unwanted CAV in vaccines not only influences the epidemiology of chicken infectious anemia disease, but may also lead to vaccine failure and confusing results when vaccine responses are monitored. To detect CAV in contaminated vaccines, nucleic acid testing (unlike conventional testing) has a shorter processing time and does not require cell culture or live animals.
The aim of the current study was to develop a TaqMan real-time polymerase chain reaction (PCR) assay to detect and quantify CAV in poultry vaccines and investigate CAV contamination in Razi live Newcastle disease vaccines. The TaqMan real-time PCR assay was set up, optimized, and validated in successive experiments. A standard plasmid pUC-VP2 containing viral protein 2 of CAV was constructed and used in the assay to generate a standard curve to quantify CAV genomes.
A clear linear correlation was observed between threshold cycle (Ct) values and plasmid copy numbers in the amplification plots of 10-fold serial dilution of the plasmid. Total DNA of three samples of each of four different Razi live Newcastle disease vaccines, namely LaSota, B1, clone.12IR, and thermo-resistant strains were extracted and subjected to real-time PCR assay. No CAV contamination was detected in the Razi Live Newcastle vaccines. The developed TaqMan real-time PCR assay provides a quick, specific, and sensitive method for use in detecting CAV in quality control vaccine testing and viral load studies.

Heteroleptic copper(II) complexes of prenylated flavonoid osajin behave as selective and effective antiproliferative and anti-inflammatory agents

Heteroleptic copper(II) complexes, containing prenylated flavonoid osajin isolated from the fruits of Maclura pomifera Schneid., were prepared and thoroughly characterized, including single crystal X-ray analysis. Some of the following complexes of the general composition [Cu(L)(bpy)]NO3 (1), [Cu(L)(dimebpy)]NO3·2MeOH (2) [Cu(L)(phen)]NO3·H2O (3), [Cu(L)(bphen)]NO3 (4) and [Cu(L)(dppz)]NO3 (5), where HL stands for 3-(4-hydroxyphenyl)-5-hydroxy-8,8-dimethyl-6-(3-methylbut-2-ene-1-yl)-4H,8H-benzo[1,2-b:3,4-b’]dipyran-4-one (osajin), bpy = 2,2′-bipyridine, dimebpy = 4,4′-dimethyl-2,2′-bipyridine, phen = 1,10-phenanthroline, bphen = 4,7-diphenyl-1,10-phenanthroline and dppz = dipyrido[3,2-a:2′,3′-c]phenazine, were also monitored for their solution stability and interactions with cysteine and glutathione by mass spectrometry.
  • The in vitro cytotoxicity of the complexes was evaluated against a panel of eight human cancer cell lines: (MCF-7, HOS, A549, PC-3, A2780, A2780R, Caco-2, and THP-1). The results revealed high antiproliferative activity of the complexes with the best IC50 values of 0.5-3.4 μM for complexes (4) and (5), containing the bulkier N,N’-donor ligands (bphen, and dppz, respectively).
  • The complexes also revealed a relatively low toxicity towards human hepatocytes (IC50 values are higher than 100 μM in some cases), and thus proved to be highly selective towards the cancer cells. On the other hand, the complexes showed a strong in vitro nuclease effect using the model pUC-19 plasmid.
  • In the model of lipopolysaccharide-stimulated (LPS) THP-1 monocytes, the complexes revealed ability to lower the activity of nuclear factor kappa-B/activator protein 1 (NF-κB /AP-1) system and decrease the secretion of tumor necrosis factor alpha (TNF-α). Thus, the complexes have been identified as strong antiproliferative and anti-inflammatory compounds.

A novel method for DNA delivery into bacteria using cationic copolymers

Amphiphilic copolymers have a wide variety of medical and biotechnological applications, including DNA transfection in eukaryotic cells. Still, no polymer-primed transfection of prokaryotic cells has been described. The reversible addition-fragmentation chain transfer (RAFT) polymer synthesis technique and the reversible deactivation radical polymerization variants allow the design of polymers with well-controlled molar mass, morphology, and hydrophilicity/hydrophobicity ratios.
RAFT was used to synthesize two amphiphilic copolymers containing different ratios of the amphiphilic poly[2-(dimethyl-amino) ethyl methacrylate] and the hydrophobic poly [methyl methacrylate]. These copolymers bound to pUC-19 DNA and successfully transfected non-competent Escherichia coli DH5α, with transformation efficiency in the range of 103 colony-forming units per µg of plasmid DNA. These results demonstrate prokaryote transformation using polymers with controlled amphiphilic/hydrophobic ratios.

One-step construction of a food-grade expression system based on the URA3 gene in Kluyveromyces lactis

Proteins from food-grade expression systems can be used in food products and medical applications. Herein, we describe a one-step method of constructing an expression vector in Kluyveromyces lactis by combining a URA3-deficient strain and a plasmid vector with no drug-resistant selection. Adjacent DNA elements of the vector were assembled in a targeted manner through a reaction with a special recombinase to form a plasmid vector using a one-step reaction.
The unnecessary fragments containing the pUC origin and the ampicillin resistance gene were removed, and the vector was isolated and purified before transformation. A single transformation of the vector can produce a URA3-deficient strain. PCR assay, sequencing, and western blot analysis all indicated that the method of vector construction and target protein expression (mCherry and human serum albumin) were successful. This method may potentially be applied to any species containing the URA3 gene; this system has the potential to become a safe and powerful tool for promoting protein expression in food-safe species.

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