What Are Transformation, Transfection & Transduction?
One of the pillars of modern day molecular biology uses techniques to manipulate DNA sequences (such as plasmids, knockout gene constructs, etc.) and introduce them into a host cell to test their effects. However, getting the DNA into cells can take different routes. Those unfamiliar with the field may be wondering “what is plasmid transduction?” Or have heard the terms transformation, transfection, and transduction, but are uncertain as to the differences and similarities between these techniques. Although these terms have some overlap, and so their usage is often confusing or incorrect.
What Is Plasmid Transformation?
Transformation is, simply put, the process of altering a cell’s genetic code through the uptake of foreign DNA from the environment. Plasmid transformation is used to describe the (non-viral) horizontal gene transfer of plasmids between bacteria. While transformation likely happens in the natural world, scientists have harnessed this process to their own ends, enabling replication of lab-manipulated plasmids and expression of desired recombinant DNA sequences.
The process is relatively simple; scientists make the membranes of bacterial cells permeable to DNA either through chemical means or via electrical stimulation. These cells, now termed ‘competent cells,’ will readily uptake plasmid DNA from their surroundings. Once the DNA molecule of interest is introduced to these competent cells, the bacteria have now been plasmid transformed. The transformed cells then can be selected from the untransformed cells by inclusion of an antibiotic to kill off the untransformed cells. Typically, this occurs as the plasmid will express an antibiotic resistance gene to protect the transformed cells and ensure maintenance of the plasmid over time and cell divisions. In the process, many replicons of the plasmid will be created and passed to daughter cells.
What Is Plasmid Transfection?
Transfection is a type of plasmid transformation, typically that of animal cells, instead of bacteria. This process is a bit more complicated than your run-of-the-mill transformation, as many lab-cultured eukaryotic cells do not natively uptake and replicate foreign DNA. Still, scientists have discovered many ways in which plasmids and other foreign DNA can be introduced to cells.
Much like methods for bacteria, there are both chemical and physical methods of transfection produce transient holes in the cell membrane and get uptake of foreign DNA. These methods work similarly to the those outlined for bacterial transformation, as they all are designed to make the cell membrane more permeable. The method by which they do so is different from bacteria, though, instead using cationic lipids, micelles, lasers, or even particle guns. These methods have their pros and cons, but ultimately will depend on the resources available and the preference of the researcher.
What Is Transduction?
The final prominent method, transduction, is unique from the other two methods. Transduction is the process of using a virus to mediate the delivery of DNA fragments or plasmids into a cell, either prokaryotic or eukaryotic. This technique harnesses the natural function of viruses to inject DNA into the infected host, but with a twist. Scientists can modify the viral nucleic acids to contain specific DNA sequences of interest. There are many different types of viruses that can be manipulated to introduce recombinant nucleic acids into host cells. For example, bacteriophage introduce DNA into bacteria, and lentiviruses or adenoviruses into human cells. Using these modified viruses, researchers incorporate foreign DNA into the host genome (such as using lentiviruses or bacteriophage) or transiently express desired recombinant nucleic acids (such as using adenoviruses).
In order to perform a transduction, you need a cell-line of interest and a virus that infects that cell line. This method can be more difficult than the other methods discussed here, since the virus must be grown and maintained in culture, sometimes needs to be modified to be non-infectious to humans, and the DNA of interest must be packaged into the viral particle before infection of new host cells can occur. Despite the challenges to overcome, viral transduction is an excellent way to perform stable, long term transformations and transfections in the lab environment.