Lecture 8 Flashcards
What did the Davis experiment show?
Cells needed cell to cell contact for transfer of DNA to occur
Discovery of transduction
- not just conjugation is occurring to result in a recombination of DNA
- the fine filter allows the transfer of the liquid but not the bacteria - so something is transferring to the other side to obtain the phototrophs
Merchandise of generalised transduction
- bacteria phage injects intself and takes over the donor bacterium
- every so often the bacterial chromosomal DNA gets packaged into the head by accident instead of phage DNA
- this bacteriophage can then land on the recipient bacterium and inject the DNA from the previous bacterium
What is the amount of DNA that can be transduced limited by?
How much DNA can be packaged into a phase head
What is phage host specificity determined by
Partially by cell-surface receptors/transduce genes into same species
Mapping by transduction key points
- the amount of DNA that can be transduced is limited but the amount of DNA that can fit into the phage head - usually about 90kb for a common transducing phage.
- two crossovers are required to incorporate the transduced DNA into the recipient genome. The further apart two co-transduced markers are, the more likely they are to be separated by recombination
(- if a bacteria phage picks up a 90kb length of DNA and it contains two genes, then those two genes must be within 90kb of eachother
- the genes are closer together they are more likely to get incorporated into the chromosome at the same time)
What does this conclude
- Both Azi and Thr can be co-transduced with Leu and therefore each locus is within 90kb of leu
- Azi is closer to Leu as it is co-transduced with Leu at a higher frequency than Thr is.
What does this conclude
- Thr and leu can be co-transduced at low frequency therefore lie within 90kb of eachother
- Thr and azi cannot be co-transduced and are therefore more then 90 kb apart
What does this conclude
If you select for Leu plus Thr, Azi is never co-transduced. Confirms that the distance between Thr and Azi is greater then 90 kb
Summary of generalised transduction
- phage accidentally packages bacterial DNA and injects into recipient —-> incorporated by recombination
- any gene can be transduced at low frequency
- amount of DNA transferred limited by size of phage head ~90kb
- generalised transduction useful for high result ion mapping by analysing frequency of co-transduction
- useful for strain construction
What is transformation
- uptake of naked DNA into a compenent recipient cell
Griffiths discovery of transformation
Transformation occurs naturally in how many species of bacteria?
80
Transformation occurring in these 80 species of bacteria is dependant on…
Specialised cell state called competence
I don’t understand what this slide is getting at
- a way of generating diversity
- joining mutations together
Transformation
- might have machinery in the membrane that recognise a specific sequence
- DNA is degraded - releases nucleotides bacteria can make use of
Example of transformation in S. pneumoniae
- transformation from streptococcus susis to S. pneumoniae can cause antibiotic resistance
- S. pneumoniae can become penicillin-resistant due to mosaic pbb (penicillins binding protein_ genes
- mosaic pbp genes encode proteins with reduced affinity for penicillin resistance
Take home
