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How do plasmids transfer useful genes between bacterial cells?
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Nucleic acid
A portion of the polynucleotide chain of deoxyribonucleic acid (DNA), with an inset showing the corresponding pentose sugar and pyrimidine base in ribonucleic acid (RNA).
Plasmids transfer genetic information between bacterial cells primarily through a process known as horizontal gene transfer. While plasmids are extrachromosomal, circular DNA molecules that replicate independently of the bacterial chromosome, they facilitate the spread of useful traitsāsuch as antibiotic resistanceāvia three main mechanisms:12
- Conjugation: This is the most direct method, involving cell-to-cell contact. Donor cells containing a conjugative plasmid produce a structure called a sex pilus, which attaches to a recipient cell. A conjugal bridge then forms, allowing the plasmid to be transferred from the donor to the recipient.2
- Transformation: Bacteria can take up free fragments of DNA, including plasmids, directly from their surrounding environment. For this to occur, the recipient bacteria must be in a "competent" state, which allows them to bind and internalize the external genetic material.32
- Transduction: In this process, DNA is transferred between bacteria by a bacteriophage, a virus that infects bacteria. The virus acts as a vehicle, protecting the DNA from environmental degradation and injecting it directly into the recipient cell.2
Once acquired, this new genetic material can be incorporated into the recipient's genome through recombination or insertion, enabling the bacteria to adapt and evolve.3