Specialized transduction: Steps

Transduction is one process of transferring a bacteria’s DNA (deoxyribonucleic acid) to another with the help of a virus (bacteriophage). Genetic transfer of host genes by bacteriophage occurs in two ways; generalized transduction and specialized transduction. Bacteria transfer their gene through other processes like transformation and conjunction. The bacteriophage and the target bacteria mediate the transduction of the bacterial gene, for example. P22 bacteriophage mediates the transduction (generalized and specialized) in the Salmonella typhimurium.   

Specialized transduction is the process where the phage carries only a specific part of the host’s (bacteria) DNA as a part of the viral genome. It only occurs during the lysogenic cycle of bacteriophage and in some temperate phages. But specialized transduction is a highly efficient gene transfer mechanism.

Temperate phage is the phage that undergoes a lysogenic cycle for growth and multiplication.

Lytic and Lysogenic Cycle

Before discussing the steps of specialized transduction, let us briefly discuss the lytic and lysogenic cycle of bacteriophage. 

The lytic cycle is the process of viral multiplication where the phage hijacks the host cellular machinery to produce new viral progeny leading to the lysis of the host cell. It occurs in specific steps: phage attachment to the host, entry inside the cell, phage replication, synthesis of nucleic acid and proteins, assembly of proteins and nucleic acid, and release. The generalized transduction process occurs during the protein and nucleic acid assembly in the lytic phage. While assembling the viral genome, the host gene is sometimes packed in the viruses. The gene is then transferred to the new host (bacteria) after the newly formed phage infects it.  

The lysogenic cycle is the cycle of bacteriophage where during multiplication, there is no lysis (death) of the bacteria because the virus does not use the machinery of the bacteria. Instead, the viral gene carries a particular portion of the bacterial gene. This type of multiplication gives rise to the new viruses only when the host conditions deteriorate due to natural conditions like lack of nutrition, suitable environment, etc. The new virus then transfers only the specific part of DNA it has carried to the newly infected host. 

Lytic and lysogenic cycle
Lytic and lysogenic cycle

Steps of Specialized Transduction

Specialized transduction
Bacterial DNA specialized transduction

The specialized transduction starts after a complete lysogenic cycle and has the following steps: 

  1. The first lysogenic cycle begins when a bacteriophage infects the donor bacteria.
  2. After the entry into the donor bacteria, improper splicing during replication leads to the integration of bacterial DNA into the phage DNA.
  3. Now, the newly formed bacteriophage with a part of the DNA of the donor host attaches to a new host (recipient bacteria).
  4. The virus enters the recipient bacteria by endocytosis.
  5. During another lysogenic cycle, the part of the donor bacteria’s DNA gets transduced into the recipient’s DNA. 
  6. Then, the recipient bacteria express the newly integrated genetic traits along with its older traits.

Comparison Between Normal Lysogenic cycle and Specialized Transduction

Let’s contrast the normal lysogenic cycle and the mechanism of transduction.

  1. When a lambda phage is in the lysogenic cycle, the phage genome becomes integrated into the host (bacteria) DNA at a specific site.
  2. Viral DNA replicates under host control.
  3. On induction: The viral DNA separates from the host DNA by a process that is the reverse of integration
  4. During the normal event: Lambda DNA is excised as a unit.
  5. During the rare event, lambda phage excise incorrectly; some adjacent bacterial genes are also excised along with phage DNA, whereas some phage DNA is left behind. These phages are called defective lambda phages.
  6. There are two possibilities when the lysate containing defective lambda phage is mixed with a sensitive bacterial population.
  1. The bacterial DNA may be integrated into the host chromosome during lysogenization, and
  2. The DNA may be replicated in the recipients as part of lytic infection.

Examples of Transduction in Bacterial Population 

Transduction occurs in a variety of bacterial populations, including:

  1. Escherichia coli
  2. Pseudomonas spp
  3. Salmonella spp
  4. Staphylococcus spp

References:

  • Jain, P., Hsu, T., Arai, M., Biermann, K., Thaler, D., & Nguyen, A. et al. (2014). Specialized Transduction Designed for Precise High-Throughput Unmarked Deletions in Mycobacterium tuberculosis. Mbio, 5(3). DOI: 10.1128/mbio.01245-14
  • transduction (prokaryotes) | Learn Science at Scitable. (2022). Retrieved 9 August 2022, from https://www.nature.com/scitable/definition/transduction-prokaryotes-292/
  • Specialized Transduction. (2008). Encyclopedia Of Genetics, Genomics, Proteomics And Informatics, 1849-1849. DOI: 10.1007/978-1-4020-6754-9_15913
  • Fields, B., Knipe, D., & Howley, P. (2007). Fields’ virology (6th ed.). Philadelphia, Pa.: Wolters Kluwer Health/Lippincott Williams & Wilkins.

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.

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