LGT Flashcards
(32 cards)
What are the three mechanisms for LGT?
- Transduction
- Conjugation
- Transformation
What is transduction?
Infection by bacteriophages, which are selfish
What is conjugation?
Transfer and copy of plasmids between cells
What is transformation?
Uptake of naked DNA from the environment
How many ‘house-keeping’ genes does the bacterial genome contain?
2000
How many extra genes does the bacterial genome contain?
18,000
Can bacteria carry more than one plasmid?
Yes
Can bacteria carry different types of plasmids?
Yes
How many plasmids can E. coli carry?
0-11
How many different types of E. coli plasmids are there?
100s
In conjugation, where is the transfer machinery?
Carried by the plasmid
Is there a risk involved in conjugation?
Yes, a high risk of segregational loss of the plasmid during transfer
There are two types of selection that act on plasmids. What is individual selection?
Acts on the fitness of the plasmid itself
What 3 factors favour increased plasmid copy number under individual selection?
- Plasmid avoids segregational loss
- Plasmid outcompetes other plasmids
- There is a high probability of conjugation between cells
There are two types of selection acting on plasmids. What is group selection?
Acts on the fitness of the host
Under group selection on plasmids, when does the fitness of the host decrease? Why?
With high copy number as it is a metabolic burden
Who looked at the effects of copy number in yeasts? Which genus?
Harrison et al., 2012
Saccharomyces yeasts
Harrison et al. 2012:
Which plasmid did they study in Saccharomyces? What does it contain?
2 μm
Encodes about 4 genes
Harrison et al., 2012:
What was the fitness burden of 2 μm plasmids per copy?
Can it be stably maintained?
0.17% reduction in fitness per copy
No, cost is higher than expected
What does policing in plasmids involve?
Inhibitors (of replication) and obedience (affinity to inhibitor)
What is the point of a plasmid policing itself?
It can maintain lower copy numbers, creates a trade of between selfishness and longevity.
If plasmid holds back in copy number NOW, it will not decrease the fitness of the host too much and can be maintained for longer.
Who described how RM systems work?
Kobayashi, 2001
Kobayashi, 2001:
What is an RM system?
Restriction-modification
Restriction enzyme cuts and modification enzyme modifies, e.g. methylation
Self DNA is methylated to protect from cutting, restriction enzyme cuts ‘other’ DNA
Who described the hok/sok system?
Gerdes et al., 1990