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Short answer
Transformation in bacteria is the process by which foreign DNA is introduced into a cell. It happens naturally in some species, and labs make it happen on demand by preparing competent cells, adding DNA, giving a brief heat shock or electrical pulse, letting the cells recover, and then selecting survivors on antibiotic plates. Each step has a job, and most failed transformations trace back to one of them.
Definition and scope
Addgene’s protocol defines transformation as “the process by which foreign DNA is introduced into a cell.” The same idea appears in the questions people search for in different words: what is transformation in bacteria, transformation of DNA and transformation bacteria definition all point at DNA entering a bacterial cell from outside, not at DNA being copied inside it.
This guide covers the bacterial lab technique. It is not about transfection of animal cells, which is covered in transfection methods, controls and biosafety.
Natural versus laboratory transformation
Thermo Fisher Scientific describes bacterial transformation as a natural process in which cells take up foreign DNA from the environment. It gives the natural frequency as 10-2 to 10-10, varying widely between species. Because natural uptake is unreliable across the species labs work with, competency “can be artificially introduced (chemically or by electroporation).”
Chemical competence
Thermo Fisher credits Mandel and Higa (1970) with showing that calcium ions (Ca2+) combined with a brief rise in temperature, the heat shock, increase membrane permeability to DNA.
Electroporation
Electroporation applies an electrical field to enhance DNA uptake; short, high-voltage pulses make the membrane transiently permeable. For preparation, efficiency and settings see competent cells and electroporation parameters and buffers; the equipment is described in what is an electroporator.
Steps of transformation in bacteria
The steps of transformation in bacteria (also searched as transformation bacteria steps and transformation steps in bacteria) run in the same order in most protocols. The values below are the ones Addgene gives in its bacterial transformation protocol (last updated Nov. 13, 2017); the instructions that come with the cells you use take precedence.
1. Competent cells and DNA
Cells that have been made competent are combined with the DNA to be introduced, typically a plasmid. Addgene recommends running a positive control plasmid alongside, and notes that many vendors include one.
2. Heat shock (chemical method)
Addgene places the bottom one-half to two-thirds of the tube in a 42°C water bath for 30 to 60 seconds, and says 45 seconds is usually ideal, though the best time varies with the competent cells.
3. Recovery (outgrowth)
Addgene adds 250 to 1,000 µL of LB or SOC medium without antibiotic and incubates in a 37°C shaking incubator for 45 minutes. This gives the cells time to make the antibiotic resistance proteins; Addgene notes it is less critical for ampicillin.
4. Selection on antibiotic plates
The cells are spread onto LB agar plates containing the appropriate antibiotic. Addgene suggests plating 50 µL on one plate and the rest on a second so that at least one plate yields single colonies.
What each step is for, and what to check when it fails
Laying the protocol out as a diagnostic links each stage to the first thing to check. The rows draw on the Addgene protocol and, for the role of calcium, the Thermo Fisher overview.
| Stage | What it is for | First check if there are no colonies |
|---|---|---|
| Positive control plasmid | Shows whether the cells and the workflow can transform at all | Run it in parallel; many vendors include one |
| Heat shock | Brief temperature rise that works with Ca2+ to let DNA in | Time and temperature in the cells’ instructions; Addgene’s range is 30 to 60 seconds at 42°C |
| Recovery in medium without antibiotic | Lets cells express the resistance proteins before selection | Medium was LB or SOC with no antibiotic, and the 45-minute 37°C shake took place |
| Antibiotic plate | Allows only cells that took up the plasmid to grow | Plate antibiotic matches the plasmid’s resistance gene (Addgene’s first check) |
Transformation versus transduction
Transformation is uptake of DNA from the surroundings. Transduction is different: Thermo Fisher credits Zinder and Lederberg (1952) with showing that phages could package bacterial DNA, chromosomal or plasmid, and carry it to another bacterial host. In transformation no virus is involved in the transfer.
Where it matters for labs and supply decisions
Because the workflow depends on four matched components, a purchasing or inventory check can follow the same list. Based on the Addgene protocol, a lab setting up bacterial transformation needs:
- Competent cells, chemically competent for the heat-shock method or prepared for electroporation, with the supplier’s instructions for the cells in use.
- A positive control plasmid (check whether the cell supplier includes one).
- LB or SOC recovery medium without antibiotic.
- LB agar plates containing the antibiotic that matches the plasmid’s resistance gene.
- A 42°C water bath for heat shock, and a 37°C shaking incubator for recovery.
The broader workflow that transformation feeds, including cloning the insert, is described in gene cloning, and the organisms themselves in what is bacteriology.
Common misunderstandings
- Heat shock is not a universal step. It belongs to the chemical (calcium) method; electroporation uses a high-voltage pulse instead.
- Recovery is not optional filler. It is what allows resistance proteins to be made before the cells meet the antibiotic, although Addgene notes it is less critical for ampicillin.
- Transformation is not transduction. The first is direct DNA uptake; the second uses phages as carriers.
- Not every plate failure is a technique failure. Addgene’s first check for no transformants is that the plate antibiotic matches the plasmid’s resistance gene.
FAQ
What is transformation in bacteria?
The introduction of foreign DNA into a bacterial cell. It occurs naturally in some species and is induced in the lab with chemical competence or electroporation.
What are the steps of transformation in bacteria?
Prepare competent cells and add DNA, apply a heat shock or an electrical pulse, allow recovery in antibiotic-free medium, then plate on selective antibiotic agar.
What does heat shock do?
Combined with calcium ions, a brief rise in temperature increases cell membrane permeability to DNA, a method credited to Mandel and Higa (1970).
What is transformation in biology?
For bacteria, it means uptake of foreign DNA by a cell, as defined above.
Sources
- Addgene, Bacterial Transformation (protocol last updated Nov. 13, 2017; checked 2026-10-29).
- Thermo Fisher Scientific, Competent Cell Basics (checked 2026-10-29).
