In-stock competent cells across a range of strains, with high transformation efficiency and reliable performance.
The default cloning strain — stable transformation efficiency, ideal for routine plasmid amplification and blue-white screening.
A standard strain for protein expression, carrying T7 RNA polymerase, compatible with IPTG-inducible systems.
Suited to amplifying plasmids with repetitive/unstable sequences (such as lentiviral vectors), reducing the risk of recombination.
A high-efficiency cloning strain, well suited to large fragments or low-concentration DNA transformation.
Cloning strains like DH5α are engineered for high transformation efficiency and stable maintenance of plasmids without recombination or loss — purpose-built for amplification. Expression strains like BL21(DE3) carry a T7 RNA polymerase system optimized for producing large amounts of a foreign protein. The two aren't interchangeable — amplifying a plasmid in an expression strain risks unexpected recombination, while a cloning strain has no ability to drive induced expression at all.
The recombinase system in standard strains like DH5α makes it easy for plasmids with long repeats or unstable structures (such as the LTR long terminal repeats in lentiviral vectors) to undergo intramolecular recombination and end up structurally wrong. Strains like Stbl3 are specially engineered with suppressed recombinase activity, significantly lowering the odds of these unstable plasmids going wrong during amplification.
Transformation efficiency is usually expressed as colonies formed per microgram of plasmid DNA (cfu/μg). Standard chemically competent cells typically fall in the 10⁷–10⁸ cfu/μg range, while ultra-high-efficiency chemical or electrocompetent cells can reach 10⁹–10¹⁰. The right choice depends on the downstream application — routine cloning is usually fine with standard efficiency, while library construction and similar work call for higher-efficiency competent cells.
Chemical transformation (heat shock) is simple and low-cost, and is the standard default choice. Electroporation is generally more efficient, especially for large plasmids or applications that demand very high transformation efficiency (such as library construction), but it requires a dedicated electroporator and somewhat more careful technique — weigh the choice against your experimental needs and available equipment.