The expression vectors with inserted antibiotic resistance genes are the mainstream recombined expression system, and the use of antibiotics to avoid the growth and domination of plasmid free cells during fermentation. However, antibiotic residues in protein products often cause allergic reactions in the body, and the widespread use of resistance genes has led to the emergence of more and more resistant strains in the environment. Besides, antibiotics can contaminate biomass or production product, these contaminations are intolerable in industrial and medical perspectives. In order to ensure no antibiotic left in the final product when using antibiotics, it is necessary to demonstrate the residual antibiotic level and remove them, which are also expensive. Therefore, the use of antibiotic-free systems has become an inevitable trend in biomanufacturing industry.
Currently, several strategies have been discovered as alternatives to reduce the rate of plasmid-free cells overtaking the culture. One of them is toxin/ antitoxin system, which uses postsegretional killing genes to induce host cell killing when plasmid is loss.
Profacgen can provide a new and highly effective stabilization system. This system is based on two kinds of genes, the toxin gene which can cause cell death is inserted in the genome of expression strain. The antitoxin gene located in the expression plasmid, the antitoxin acts as an inhibitor of toxin. The expression plasmids with antitoxin gene and gene of interest are induced into host strain. When the plasmid is present in the cell, the antitoxin can counteract the toxin, if the plasmid is lost, the toxin can cause the cell death. With this system, stable and high protein production is achieved and no antibiotic added into the production process.