What is transduction in microbiology definition process and types
Transduction is a mode of genetic transfer from one bacteria to another through a virus. There is no direct contact between the bacterial cells. The other ways of genetic recombination in bacteria include transformation and conjugation.
In this process, bacteriophages, which infect bacteria, use host cells to multiplicate and while assembling they sometimes pack the bacterial DNA with them. Later, when these viruses infect new bacterial cells, the bacterial genome that they carry may get inserted into the host genome.
Transduction is commonly used in genetic engineering for inserting foreign DNA into the host cell.
Transduction was discovered by Zinder and Lederberg in Salmonella. Hershey and Chase used transduction as a tool to confirm that DNA is the genetic material.
Bacterial Transduction Steps
In transduction, the transfer of bacterial DNA depends on viral infection. The steps involve:
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Infection of the bacterial cell by bacteriophage.
The virus uses the host machinery to make multiple copies either directly by the lytic cycle or first gets incorporated into the bacterial genome by the lysogenic cycle and followed by the lytic stage.
During assembly of bacteriophages, the bacterial genome also gets packed by mistake in the viral head alongside the viral genome. In the lysogenic cycle, during excision of prophage, some parts of the bacterial genome that flank the prophage are also excised and go inside the assembled viral head together with the viral genome.
When these viruses infect another bacterial cell, they inject the viral DNA as well as donor DNA into the host cell.
The bacterial DNA either forms plasmids or gets inserted into the recipient DNA if it is homologous to the recipient genome. Most of the time it remains as an extrachromosomal DNA. It can also get inserted with the prophage if it is a temperate phage. So the fate depends on the portion of bacterial DNA and also on the nature of bacteriophages.
Types of Transduction
Transduction is common in both virulent and temperate phages, i.e. by lytic or lysogenic cycle. Transduction is of two types:
Generalized Transduction – In this, the phage can carry any part of DNA.
Specialized Transduction – In this, the phage carries only the specific part of DNA.
Generalized Transduction
Generalized transduction can occur by both lytic or lysogenic cycle. Here, any random part of DNA gets packed in bacteriophages by mistake along with the viral genome. It occurs at the lytic stage of the phage life cycle.
When the virus-containing bacterial DNA infects another cell, it can get inserted into the host genome or if it was a plasmid, then it can reform the plasmid.
Generalized transduction is used to study linkage information, gene mapping, comparing genomes of two different bacteria, mutagenesis, etc.
Example of generalized transduction includes E.coli transduction by P1 phage.
Specialized Transduction
Specialized transduction can occur only through the lysogenic cycle, i.e. by temperate phage. Here, only the specific part of the bacterial DNA is packed into the virus. It occurs when the prophage, i.e. viral DNA, which gets inserted into the bacterial genome in the lysogenic cycle excises.
When prophage excises from bacterial DNA, some parts of bacterial DNA, which are flanked on both sides of the prophage are also excised. Here, the newly packed phage genome consists of both bacterial and viral genomes.
Later, when the virus with the recombinant genome infects a new bacterial cell, the bacterial gene also gets inserted into the host genome with the viral genome through lysogeny. The recipient cell now shows the newly acquired characteristics.
Specialized transduction is commonly used for isolation and insertion of genes of choice.
Example of specialized transduction includes E.coli transduction by 𝝀 phage.
Application of Transduction
Transduction is one of the most important tools for genetic engineering.
Transduction is used to insert the genes of choices in animals and plant cells to modify the genetic constituents and get the desired characteristics.
It can be used for gene therapy. It has huge potential to cure genetic diseases.
It is an important tool in genetics and molecular biology research.
FAQs on Transduction in Microbiology and Bacterial Gene Transfer
1. What is transduction in microbiology?
Transduction in microbiology is a process of horizontal gene transfer in which bacterial DNA is transferred from one bacterium to another by a bacteriophage (virus that infects bacteria).
- It occurs when a bacteriophage accidentally packages bacterial DNA.
- The phage then injects this DNA into another bacterial cell.
- The transferred DNA may recombine with the recipient’s genome.
2. How does transduction occur in bacteria step by step?
Transduction occurs when a bacteriophage transfers bacterial DNA from one cell to another during infection.
- 1. Infection: A bacteriophage infects a donor bacterium.
- 2. DNA degradation: Host bacterial DNA is fragmented during the lytic cycle.
- 3. Packaging error: Some phage particles mistakenly package bacterial DNA.
- 4. New infection: The phage infects another bacterium.
- 5. Recombination: Donor DNA integrates into the recipient genome.
3. What are the types of transduction?
The two main types of transduction are generalized transduction and specialized transduction.
- Generalized transduction: Any bacterial gene can be transferred due to random DNA packaging during the lytic cycle.
- Specialized transduction: Only specific genes near the prophage insertion site are transferred during the lysogenic cycle.
4. What is generalized transduction?
Generalized transduction is a type of transduction in which any bacterial gene can be transferred by a bacteriophage.
- Occurs during the lytic cycle.
- Bacterial DNA fragments are accidentally packaged into phage heads.
- The phage injects this DNA into another bacterium.
5. What is specialized transduction?
Specialized transduction is a type of transduction where only specific bacterial genes adjacent to a prophage are transferred.
- Occurs during the lysogenic cycle.
- A prophage integrates into the bacterial chromosome.
- Improper excision of the prophage carries nearby bacterial genes.
6. What is the difference between generalized and specialized transduction?
The main difference between generalized and specialized transduction is the range of genes transferred.
- Generalized transduction: Transfers any gene; occurs in the lytic cycle; random DNA packaging.
- Specialized transduction: Transfers specific genes; occurs in the lysogenic cycle; due to improper prophage excision.
7. What role do bacteriophages play in transduction?
Bacteriophages act as vectors that carry bacterial DNA from one cell to another during transduction.
- They infect bacterial cells and replicate inside them.
- They mistakenly package bacterial DNA into phage particles.
- They inject this DNA into a new host bacterium.
8. Why is transduction important in bacterial evolution?
Transduction is important in bacterial evolution because it promotes genetic diversity and adaptation.
- It spreads antibiotic resistance genes.
- It transfers virulence factors between bacteria.
- It enhances survival in changing environments.
9. How is transduction different from transformation and conjugation?
Transduction differs from transformation and conjugation in the method of DNA transfer.
- Transduction: DNA transfer via bacteriophages.
- Transformation: Uptake of naked DNA from the environment.
- Conjugation: Direct cell-to-cell transfer through a pilus.
10. Can you give an example of transduction in bacteria?
An example of transduction is the transfer of toxin genes in Corynebacterium diphtheriae by a bacteriophage.
- A lysogenic phage carries the gene for diphtheria toxin.
- When the phage infects a non-toxigenic bacterium, it integrates into its genome.
- The bacterium gains the ability to produce toxin.
