Bacterial transformation
Say it: bak-TEER-ee-ul trans-fur-MAY-shun
Bacterial transformation is the uptake of free DNA from the surroundings by a bacterial cell, which can then gain the genes that DNA carries.
Definition
What is bacterial transformation?
Bacterial transformation is a kind of horizontal gene transfer: a bacterium takes in naked DNA, meaning DNA not packaged in a virus or a cell, and keeps the genetic information it carries. In nature the DNA usually comes from neighboring cells that have died and burst. Frederick Griffith first saw the effect in 1928, when harmless pneumococci turned deadly after being mixed with heat-killed virulent ones, and in 1944 Oswald Avery, Colin MacLeod and Maclyn McCarty proved that the transforming agent was DNA.
Only cells in a state called competence can take up DNA. Naturally competent species, such as Streptococcus pneumoniae, Bacillus subtilis and Neisseria, switch on a set of genes that build uptake machinery. One strand of the DNA is pulled inside; if it closely matches the cell's chromosome it can be swapped in by recombination, while a plasmid can instead settle in and replicate. In nature this helps spread genes for antibiotic resistance and virulence.
In the laboratory, transformation is the routine way to put recombinant plasmids into E. coli, which is not naturally competent. The cells are made competent with calcium chloride and a brief heat shock, or with an electric pulse called electroporation, then grown on a selective plate so only transformed cells form colonies.
Word parts
Where does the term “bacterial transformation” come from?
- trans-
- across, changeLatin trans
- form
- shapeLatin forma
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Terms that go with it
- PlasmidA plasmid is a small, usually circular DNA molecule that copies itself independently of the main chromosome, found mostly in bacteria.
- Recombinant DNARecombinant DNA is DNA made in the laboratory by joining pieces of DNA from different sources, often different species, into one molecule.
- Molecular cloningMolecular cloning is a set of laboratory methods for inserting a specific DNA fragment into a vector and copying it many times inside host cells.
- Bacterial conjugationBacterial conjugation is the direct transfer of DNA, usually a plasmid, from one bacterial cell to another through a pilus and close cell contact.
- TransductionIn microbiology, transduction is the transfer of bacterial DNA from one cell to another by a bacteriophage, a virus that infects bacteria.
- Antibiotic resistanceAntibiotic resistance is the ability of bacteria to survive and multiply despite an antibiotic that once killed them or stopped their growth.
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Written for biofideX in plain words, after checking these references:
- OpenStax Microbiology, 11.6 How Asexual Prokaryotes Achieve Genetic Diversity
- OpenStax Microbiology, 12.1 Microbes and the Tools of Genetic Engineering
- Lorenz and Wackernagel, Bacterial Gene Transfer by Natural Genetic Transformation in the Environment (Microbiol Rev, 1994)
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