Lecture 40. Transformation and Transduction Flashcards
What are Streptococcus pneunomiae R cells?
Rough colonies, non-pathogenic
What are Streptococcus pneunomiae S cells?
Smooth colonies, pathogenic, secrete a gelatinous polysaccharide capsule
What happened to the mouse infected with R cells?
Mouse is fine - R cells are non-pathogenic
What happened to the mouse infected with S cells?
Mouse dies - S cells are pathogenic
What happened to the mouse infected with heat killed S cells?
Mouse is fine - Dead S cells are non-pathogenic
What happened to the mouse infected with heat killed S cells and R cells?
Mouse dies
What principle did Griffith demonstrate?
The transforming principle
What is “competence”?
The ability of a bacterial cell to take up extracellular (‘naked’) DNA from the environment
Why is recombination essential in prokaryotes?
Recombination results in more “fit” organisms. Leads to spread of drug resistance, novel virulence characteristics, novel metabolic capabilities etc.
What does transformation require?
Competent cells
When does competence occur in a bacteria’s life span and why?
Just before entry to the stationary phase as cells rely on quorum sensing to do something as the cells are now at risk of dying
What is quorum sensing?
The ability to regulate genes based on population density
What pheromone do B. subtilis cells secrete?
ComX
What happens when ComX binds to ComP?
The binding of ComX and ComP set off a reaction of events leading to changes in gene expression which makes cells more competent
What DNA can B. subtilis take up?
DNA of any origin
Can all bacteria take up DNA from any origin?
No - Neisseria gonorrhoeae and Haemophilus influenzae will only take up from same species
How can the bacteria distinguish between DNA from another bacteria of the same species and from a different species?
It recognises specific DNA sequences
Uptake of DNA mechanism
- DNA bind to surface protein on cell
- Depending on species, single or double DNA enters the cell
- Bind to competence-specific protein
- RecA mediated integration
Can new traits be acquired through DNA uptake?
Yes - Gene fragment usually big enough to contain several genes
What is transduction?
Transduction is genetic exchange in bacteria mediated by bacteriophages
Transfer of DNA using a phage as a vector
What are possibly the most abundant “organisms” on earth?
Phages
Where do phages live?
Co-exist with hosts in all environments
What do phages influence?
Characteristics of host
Population dynamics
Long term evolution
Lytic Cycle
- Attachment of phage
- DNA inserted into cell, circularises, replication, transcription and translation, new virions assembled
- Lysis and release of new virions
- Cycle then repeats
