FabV/Triclosan Is an Antibiotic-Free and Cost-Effective Selection System for Efficient Maintenance of High and Medium-Copy Number Plasmids in Escherichia coli

So you want to express your protein in Escherichia coli?

Recombinant proteins have been extensively employed as therapeutics for the treatment of various critical and life-threatening diseases and as industrial enzymes in high-value industrial processes. Advances in genetic engineering and synthetic biology have broadened the horizon of heterologous protein production using multiple expression platforms. Selection of a suitable expression system depends on a variety of factors ranging from the physicochemical properties of the target protein to economic considerations. For more than 40 years, Escherichia coli has been an established organism of choice for protein production. This review aims to provide a stepwise approach for any researcher embarking on the journey of recombinant protein production in E. coli. We present an overview of the challenges associated with heterologous protein expression, fundamental considerations connected to the protein of interest (POI) and designing expression constructs, as well as insights into recently developed technologies that have contributed to this ever-growing field.

Construction of a Bacillus subtilis and Escherichia coli shuttle vector harboring the fabL gene as a triclosan selection marker

A new plasmid containing a mutated fabL gene from Bacillus subtilis as a triclosan selection marker was developed as a useful B. subtilis/E. coli shuttle vector. The pHT-FabL40 plasmid is stable in both gram-positive and gram-negative hosts with increased plasmid DNA yield in E. coli.

Construction of a novel Escherichia coli expression system: relocation of lpxA from chromosome to a constitutive expression vector

The selective marker in the plasmid-based expression system is usually a gene that encodes an antibiotic-resistant protein; therefore, the antibiotic has to add to maintain the plasmid when growing the bacteria. This antibiotic addition would lead to increase of production cost and the environment contamination. In this study, a novel Escherichia coli expression system, the lpxA deletion mutant harboring an lpxA-carrying vector, was developed. To develop this system, three plasmids pCas9Cre, pTF-A-UD, and pRSFCmlpxA were constructed. The plasmid pCas9Cre produces enzymes Cas9, λ-Red, and Cre and can be cured by growing at 42 °C; pTF-A-UD contains several DNA fragments required for deleting the chromosomal lpxA and can be cured by adding isopropyl-D-thiogalactopyranoside; pRSFCmlpxA contains the lpxA mutant lpxA123 and CamR. When E. coli were transformed with these three plasmids, the chromosomal lpxA and the CamR in pRSFCmlpxA can be efficiently removed, resulting in an E. coli lpxA mutant harboring pRSFlpxA. The lpxA is essential for the growth of E. coli; its relocation from chromosome to a constitutive expression vector is an ideal strategy to maintain the vector without antibiotic addition. The lpxA123 in pRSFlpxA can complement the deletion of the chromosomal lpxA and provide a strong selective pressure to maintain the plasmid pRSFlpxA. This study provides an experimental evidence that this novel expression system is convenient and efficient to use and can be used to improve L-threonine biosynthesis in the wild type E. coli MG1655 and an L-threonine producing E. coli TWF006.

Pharmaceuticals residues in selected tropical surface water bodies from Selangor (Malaysia): Occurrence and potential risk assessments

This study investigated the occurrence of nine pharmaceuticals (amoxicillin, caffeine, chloramphenicol, ciprofloxacin, dexamethasone, diclofenac, nitrofurazone, sulfamethoxazole, and triclosan) and to evaluate potential risks (human health and ecotoxicological) in Lui, Gombak and Selangor (Malaysia) rivers using commercial competitive Enzyme-Linked Immunosorbent Assay (ELISA) kit assays. Physicochemical properties of these rivers showed the surface samples belong to Class II of Malaysian National Water Quality Standards which requires conventional treatment before consumption. All the pharmaceuticals were detected in all three rivers except for triclosan, dexamethasone and diclofenac which were not detected in few of sampling locations in these three rivers. Highest pharmaceutical concentrations were detected in Gombak river in line of being as one of the most polluted rivers in Malaysia. Ciprofloxacin concentrations were detected in all the sampling locations with the highest at 299.88 ng/L. While triclosan, dexamethasone and diclofenac concentrations were not detected in a few of sampling locations in these three rivers. All these nine pharmaceuticals were within the levels reported previously in literature. Pharmaceutical production, wastewater treatment technologies and treated sewage effluent were found as the potential sources which can be related with pharmaceuticals occurrence in surface water samples. Potential human risk assessment showed low health risk except for ciprofloxacin and dexamethasone. Instead, ecotoxicological risk assessment indicated moderate risks were present for these rivers. Nevertheless, results confirmation using instrumental techniques is needed for higher degree of specificity. It is crucial to continuously monitor the surface water bodies for pharmaceuticals using a cost-effective prioritisation approach to assess sensitive sub-populations risk.

Use of FabV-Triclosan Plasmid Selection System for Efficient Expression and Production of Recombinant Proteins in Escherichia coli

Maintenance of recombinant plasmid vectors in host bacteria relies on the presence of selection antibiotics in the growth media to suppress plasmid -free segregants. However, presence of antibiotic resistance genes and antibiotics themselves is not acceptable in several applications of biotechnology. Previously, we have shown that FabV-Triclosan selection system can be used to select high and medium copy number plasmid vectors in E. coli. Here, we have extended our previous work and demonstrated that expression vectors containing FabV can be used efficiently to express heterologous recombinant proteins in similar or better amounts in E. coli host when compared with expression vectors containing β-lactamase. Use of small amount of non-antibiotic Triclosan as selection agent in growth medium, enhanced plasmid stability, applicability in various culture media, and compatibility with other selection systems for multiple plasmid maintenance are noteworthy features of FabV-Triclosan selection system.