L49: Transformation and Transduction

• What are the main components of a bacteriophage structure?

  Base plate, tail fibres, core, sheath, head
• From which organisms can B. subtilis take up DNA?

  Any origin
• Which organisms only take up DNA from the same species?

  Neisseria gonorrhoeae and Haemophilus influenzae
• How does B. subtilis know which DNA to take up?

  It becomes competent with a chemical signal
• What do bacteria recognize to distinguish DNA from different species?

  Specific DNA sequences
• What is a recognition sequence in DNA?

  A specific sequence that identifies DNA origin
• How can DNA be recognized from the same organism?

  By the presence of recognition sequences
• What is the mechanism for the uptake of DNA in bacteria?

  1. DNA binds to surface protein on cell
  2. DNA enters the cell (single or double stranded)
  3. Binds to competence-specific protein
  4. RecA mediated integration
• What happens if there is no recombination after DNA uptake?

  DNA will be degraded
• What can recombination convey to bacteria?

  New traits
• What is transduction in bacteria?

  Genetic exchange mediated by bacteriophages
• What is the size of phage T2?

  100 nm
• What types of genomes can phages have?

  Single or double stranded DNA or RNA
• What is the size range of phage genomes?

  A few kbp to hundreds of kbp
• What forms can phage genomes take?

  Can be circular or linear
• What is the ecological role of phages?

  Influence host characteristics and population dynamics
• Who conducted the first clinical trial of phage therapy?

  d’Herelle in 1919
• What was the outcome of d’Herelle's cholera outbreak trial?

  74 treated: 5 died
• What was discovered by Hershey & Chase in 1952?

  DNA is functional
• Why did phage therapy decline in Western Europe?

  Due to poorly controlled trials
• What are the differences between phage therapy and antibiotics?

  • Phage: species or strain specific
  • Antibiotics: broad spectrum
  • Phage: effective on biofilms
  • Antibiotics: poor on biofilms
  • Phage: fewer good studies on safety
  • Antibiotics: can cause resistance
• What is the lytic cycle of a phage?

  Attachment, DNA insertion, replication, lysis
• What is the lysogenic cycle of a phage?

  DNA integrates into the genome and stays
• What is a lysogen?

  A strain of bacteria carrying a lysogenic phage
• What is a prophage?

  A phage in lysogenic state
• How does a lysogen benefit the host?

  By suppressing lysis from other phages
• What are the two life styles of bacteriophages?

  Lytic and lysogenic
• What factors influence the decision between lytic and lysogenic pathways?

  Genetic and environmental factors
• What is a prophage?

  A viral genome integrated into a bacterial genome
• What gene does the prophage in Corynebacterium diphtheriae carry?

  The tox gene expressing diphtheria toxin
• How does the DtxR gene affect toxin production?

  It suppresses transcription of the tox gene
• What activates the repressor protein DtxR?

  Iron, acting as a co-repressor
• What happens when iron concentration is low in relation to toxin production?

  Toxin production is induced
• What is transduction in bacteria?

  Transfer of DNA using a phage as a vector
• What are the two types of transduction?

  Generalized and specialized transduction
• What occurs during generalized transduction?

  Transfer of any DNA to the recipient cell
• What is specialized transduction?

  Transfer of specific genes via lysogenic phages
• What principle did Griffith demonstrate?

  The transforming principle
• What happens during generalized transduction infection?

  Host DNA is degraded and packaged
• What is the outcome of virions that package host DNA?

  They can insert host DNA into recipient cells