- Escherichia coli (E. coli) BL21 is one of the most commonly used bacterial strains for recombinant protein expression.
- Derived from the E. coli B strain, BL21 has been genetically optimized to enhance the production of heterologous proteins.
- One of its key features is the absence of two major proteases, Lon and OmpT, which reduces the degradation of recombinant proteins and improves the stability and yield of expressed products.
- BL21 is often used in conjunction with vectors carrying T7 promoters, especially in derivatives such as BL21(DE3), which contain the λDE3 lysogen encoding T7 RNA polymerase under control of the lacUV5 promoter. Upon induction (typically with IPTG), T7 RNA polymerase is produced, driving strong expression of the target gene placed downstream of a T7 promoter.
- The BL21 strain grows rapidly, tolerates high levels of protein expression, and is relatively easy to transform, making it highly suitable for both small-scale experiments and large-scale industrial production.
- However, like other E. coli strains, BL21 lacks the ability to perform eukaryotic post-translational modifications, and high expression levels can sometimes lead to the formation of insoluble protein aggregates (inclusion bodies).
- Variants such as BL21(DE3)pLysS or BL21(DE3) CodonPlus have been developed to fine-tune expression levels or supply rare tRNAs to improve the expression of genes with non-optimal codon usage.
- Overall, E. coli BL21 remains a workhorse strain for bacterial expression systems, combining robustness, high protein yield, and reduced proteolysis, which make it indispensable in molecular biology and biotechnology laboratories worldwide.
