Genetic Engineering Technique in Virus-Like Particle Vaccine Construction

Vaccine becomes a very effective strategy to deal with various infectious diseases even to the point of eradication as in the smalpox virus. At present many conventional vaccines such as inactivated and live-attenuated vaccines. However, these vaccine methods have side effects on the population. Viral-like particle (VLP) is an alternative vaccine based on recombinant DNA technology that is safe with the same immunogenicity as conventional viruses. This vaccine has been shown to induce humoral immune responses mediated by antibodies and cellular immune responses mediated by cytotoxic T cells. With these advantages, currently various types of vaccines have only been developed on a VLP basis. VLP can be produced from a variety of recombinant gene expression systems including bacterial cell expression systems, yeast cells, insect cells, mammalian cells, plant cells, and cell-free systems.

A standardized genome architecture for bacterial synthetic biology (SEGA)

Chromosomal recombinant gene expression offers a number of advantages over plasmid-based synthetic biology. However, the methods applied for bacterial genome engineering are still challenging and far from being standardized. Here, in an attempt to realize the simplest recombinant genome technology imaginable and facilitate the transition from recombinant plasmids to genomes, we create a simplistic methodology and a comprehensive strain collection called the Standardized Genome Architecture (SEGA). In its simplest form, SEGA enables genome engineering by combining only two reagents: a DNA fragment that can be ordered from a commercial vendor and a stock solution of bacterial cells followed by incubation on agar plates. Recombinant genomes are identified by visual inspection using green-white colony screening akin to classical blue-white screening for recombinant plasmids. The modular nature of SEGA allows precise multi-level control of transcriptional, translational, and post-translational regulation. The SEGA architecture simultaneously supports increased standardization of genetic designs and a broad application range by utilizing well-characterized parts optimized for robust performance in the context of the bacterial genome. Ultimately, its adaption and expansion by the scientific community should improve predictability and comparability of experimental outcomes across different laboratories.

A Plasmid System with Tunable Copy Number

Plasmids are one of the most commonly used and time-tested molecular biology platforms for genetic engineering and recombinant gene expression in bacteria. Despite their ubiquity, little consideration is given to metabolic effects and fitness costs of plasmid copy numbers on engineered genetic systems. Here, we introduce two systems that allow for the finely-tuned control of plasmid copy number: a plasmid with an anhydrotetracycline-controlled copy number, and a massively parallel assay that is used to generate a continuous spectrum of ColE1-based copy number variants. Using these systems, we investigate the effects of plasmid copy number on cellular growth rates, gene expression, biosynthesis, and genetic circuit performance. We perform single-cell timelapse measurements to characterize plasmid loss, runaway plasmid replication, and quantify the impact of plasmid copy number on the variability of gene expression. Using our massively parallel assay, we find that each plasmid imposes a 0.063% linear metabolic burden on their hosts, hinting at a simple relationship between metabolic burdens and plasmid DNA synthesis. Our plasmid system with tunable copy number should allow for a precise control of gene expression and highlight the importance of tuning plasmid copy number as tool for the optimization of synthetic biological systems.

Overview of Bacterial and Yeast Systems for Protein Expression

Over the past decade the variety of hosts and vector systems for recombinant protein expression has increased dramatically. Researchers now select from among mammalian, insect, yeast, and prokaryotic hosts, and the number of vectors available for use in these organisms continues to grow. With the increased availability of cDNAs and protein coding sequencing information, it is certain that these and other, yet to be developed systems will be important in the future. Despite the development of eukaryotic systems, E. coli remains the most widely used host for recombinant protein expression. Optimization of recombinant protein expression in prokaryotic and eukaryotic host systems has been carried out by varying simple parameters such as expression vectors, host strains, media composition, and growth temperature. Recombinant gene expression in eukaryotic systems is often the only viable route to the large-scale production of authentic, post translationally modified proteins. It is becoming increasingly easy to find a suitable system to overexpress virtually any gene product, provided that it is properly engineered into an appropriate expression vector.

Stable recombinant gene expression from a Ligilactobacillus live bacterial vector via chromosomal integration

Disease control in animal production systems requires constant vigilance. Historically, the application of in-feed antibiotics to control bacteria and improve performance has been a much-used approach to maintain animal health and welfare. However, the widespread use of in-feed antibiotics is thought to increase the risk of antibiotic resistance developing. Alternative methods to control disease and maintain productivity need to be developed. Live vaccination is useful in preventing colonisation of mucosal-dwelling pathogens by inducing a mucosal immune response. Native poultry isolate Ligilactobacillus agilis La3 (previously Lactobacillus agilis) has been identified as a candidate for use as a live vector to deliver therapeutic proteins such as bacteriocins, phage endolysins, or vaccine antigens to the gastrointestinal tract of chickens. In this study, the complete genome sequence of L. agilis La3 was determined and transcriptome analysis was undertaken to identify highly expressed genes. Predicted promoter regions and ribosomal binding sites from constitutively expressed genes were used to construct recombinant protein expression cassettes. A series of double-crossover shuttle plasmids were constructed, to facilitate rapid selectable integration of expression cassettes into the L. agilis La3 chromosome via homologous recombination. Inserts showed 100% stable integration over 100 generations without selection. A positive relationship was found between protein expression levels and the predicted strength of the promoters. Using this system, stable chromosomal expression of a Clostridium perfringens antigen, rNetB, was demonstrated without selection. Finally, two recombinant strains, L. agilis La3::Peft-rnetB and L. agilis La3::Pcwah-rnetB, were constructed, characterised, and showed potential for future application as live vaccines in chickens. Importance Therapeutic proteins such as antigens can be used to prevent infectious diseases in poultry. However, traditional vaccine delivery by intramuscular or subcutaneous injection has generally not proven effective for mucosal-dwelling microorganisms that live within the gastrointestinal tract. Utilising live bacteria to deliver vaccine antigens directly to the gut immune system can overcome some of the limitations of conventional vaccination. In this work, Ligilactobacillus agilis La3, an especially effective gut coloniser has been analysed and engineered with modular and stable expression systems to produce recombinant proteins. To demonstrate the effectiveness of the system, expression of a vaccine antigen from poultry pathogen Clostridium perfringens was monitored over 100 generations without selection and found to be completely stable. This study demonstrates the development of genetic tools, novel constitutive expression systems and further development of L. agilis La3 as a live delivery vehicle for recombinant proteins.