Lecture Notes on Viral Transduction

Introduction to Transduction

• Transduction is the process by which a virus transfers DNA from one bacterial cell to another.
• It specifically involves the transfer of bacterial DNA, not viral DNA.

Types of Transduction

1. Generalized Transduction

   • Random fragments of host DNA are accidentally packaged into a phage during assembly.
   • When the phage infects another bacterium, it transfers the bacterial DNA from the previous host.
   • Most of the time, transferred DNA gets degraded in the new host, but occasionally it can confer advantages like antibiotic resistance.
   • Even though rare, the frequency of bacterial interactions makes these events significant.

2. Specialized Transduction

   • Involves temperate phages during the lysogenic cycle.
   • Phage DNA integrates into the host's genome, becoming a prophage.
   • During excision (returning to the lytic cycle), specific adjacent host DNA can be excised and transferred.
   • The process results in the transfer of consistent, non-random host DNA segments.

Viral Life Cycles

• Lytic Cycle

  • Phage infects host, takes over the cell machinery to replicate phage DNA.
  • Host cell is eventually lysed, releasing new phage particles.

• Lysogenic Cycle

  • Phage DNA integrates into the host genome, becoming latent as a prophage.
  • The prophage is copied with the host DNA during cell division.
  • Under stress, prophage DNA can exit, triggering the lytic cycle.

Importance of Transduction

• Contributes to genetic variability in bacteria.
• Can lead to the development of virulence factors in pathogens.
• Some diseases linked to prophage genes include:
  • Diphtheria
  • Botulism
  • Cholera
  • Virulence in Streptococcus pyogenes, including necrotizing fasciitis.

Conclusion

• Transduction, mutation, and other genetic processes are crucial for understanding bacterial evolution and pathogenesis.
• Questions can be directed to the instructor for further clarification on these topics.