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The Three Ts of Introducing Foreign DNA: Transfection, Transduction, and Transformation

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introducing foreign dna

Introducing foreign DNA into bacterial or eukaryotic cells is a common molecular biology technique. Some of the terminology involved can be confusing: transformation, transfection and transduction. What do these words actually mean? To make matters worse, sometimes people use these terms interchangeably, resulting in confusion between colleagues and collaborating labs.

Here then is your definitive guide to the three Ts of Foreign DNA insertion.


Transformation is the uptake of DNA from the environment by a bacterial cell. This phenomenon occurs in nature between bacteria of the same species. Scientists adapted transformation for propagation of plasmid DNA, protein production, and other applications. In research, transformation introduces recombinant plasmid DNA into competent bacterial cells that take up extracellular DNA from the environment. Some bacterial species are naturally competent under certain environmental conditions, but competence is artificially induced in a laboratory setting.


Transfection is the forced introduction of small molecules such as DNA, RNA, or antibodies into eukaryotic cells. Just to make life confusing, ‘transfection’ also refers to the introduction of bacteriophage into bacterial cells. But for the purpose of this article, we will focus on eukaryotic cells.

Common transfection methods include calcium phosphate, cationic polymers (such as PEI), magnetic beads, electroporation and commercial lipid-based reagents such as Lipofectamine and Fugene.


Transduction is not a biology-specific term. The common definition of transduction is ‘leading through or across.’ The term has been used to describe DNA transfer between bacterial cells by bacteriophage. However, in current research, transduction also refers to the infection of mammalian cells with a viral vector.

‘Transduction’ was first used to describe bacterial gene transfer back in the 1950s, decades before the creation of viral vectors. It’s possible that the word has been co-opted to prevent confusion, as ‘transfection’ doesn’t distinguish between the introduction of nucleic acid or viral particles into a cell.

‘Transduction’ is mostly used to describe the introduction of recombinant viral vector particles into target cells, while ‘infection’ refers to natural infections of humans or animals with wild-type viruses. There are no universally accepted differences between these two terms (a quick Google search uncovers all kind of online debate).  They are mostly used as a convenient way to differentiate between two biological mechanisms.

Clear as Mud?

In some ways, the ‘Three Ts’ terminology is arbitrary. Terms used for bacterial studies back in the mid twentieth century are now used for other applications. The development of new molecular techniques required changes in our vocabulary. Rather than technically correct definitions, these terms are now used to conveniently describe different biological research processes.

The main consideration is to make sure that all lab members and collaborators (if possible) are on the same page when it comes to terminology about introducing foreign DNA. This will prevent widespread confusion and inaccuracies during research and publication.

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