Lecture 8

Question 1

What did the Davis experiment show?

Answer 1

Cells needed cell to cell contact for transfer of DNA to occur

Question 2

Discovery of transduction

Answer 2

• 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

Question 3

Merchandise of generalised transduction

Answer 3

• 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

Question 4

What is the amount of DNA that can be transduced limited by?

Answer 4

How much DNA can be packaged into a phase head

Question 5

What is phage host specificity determined by

Answer 5

Partially by cell-surface receptors/transduce genes into same species

Question 6

Mapping by transduction key points

Answer 6

• 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)

Question 7

What does this conclude

Answer 7

1. Both Azi and Thr can be co-transduced with Leu and therefore each locus is within 90kb of leu
2. Azi is closer to Leu as it is co-transduced with Leu at a higher frequency than Thr is.

Question 8

What does this conclude

Answer 8

• 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

Question 9

What does this conclude

Answer 9

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

Question 10

Answer 10

Question 11

Summary of generalised transduction

Answer 11

• 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

Question 12

What is transformation

Answer 12

• uptake of naked DNA into a compenent recipient cell

Question 13

Griffiths discovery of transformation

Answer 13

Question 14

Transformation occurs naturally in how many species of bacteria?

Answer 14

80

Question 15

Transformation occurring in these 80 species of bacteria is dependant on…

Answer 15

Specialised cell state called competence

Question 16

Transformation is dependent on compentnce - when does competence occur?

Answer 16

When bacteria are needing to make changes to their environment, usually under stress, competence happens, but only in a small number of cells

Question 17

Can species which are not naturally transformable be made tranformable ?

Answer 17

Yes.

Question 18

I don’t understand what this slide is getting at

Answer 18

• a way of generating diversity
• joining mutations together

Question 19

Tansofmraiotn increases diversity

Question 20

Transformation

Answer 20

• might have machinery in the membrane that recognise a specific sequence
• DNA is degraded - releases nucleotides bacteria can make use of

Question 21

What is competence dependent on?

Answer 21

• growth phase
• stress
• quorum sensing (QS)

Question 22

Competence is a feature of

Answer 22

Transformation in the lifestyle of S. pneumoniae

Question 23

What does QS - quantum sensing - do?

Answer 23

Allow communication via extracellular molecular signals

• senses population density to know when more potential donor cells are available (can switch on competence if they need to)

Question 24

Induction of competence occurs only in a ____ - ________ of cells

Answer 24

Sub population

Question 25

Why do they only induce competence in some cells

Answer 25

Mixing DNA could have negative effects as well as positive

Question 26

Competent bacteria can then trigger

Answer 26

Lysis and DNA release - thus killing some of the population and competent cells taking up DNA rapidly

Question 27

What is it called when competent cells trigger lysis and DNA release from a subtraction of the population (5-20%)

Answer 27

Fratricidal (killing brothers)

Question 28

What is fraticide

Answer 28

When competent cells case some cells to die which then aid genetic recombination / assortment in recipient cells

Question 29

Transformation of S. pneumoniae

Answer 29

- capsular types can be switched by introspection transformation - about 90 types known - aid in immune evasion of this human pathogen - generation of “vaccine-escape” strains and antibiotic-resistant strains observed in vivo

Question 30

Example of transformation in S. pneumoniae

Answer 30

- 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

Question 31

Take home

Answer 31