Flashcards in LGT Deck (32)
What are the three mechanisms for LGT?
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?
How many extra genes does the bacterial genome contain?
Can bacteria carry more than one plasmid?
Can bacteria carry different types of plasmids?
How many plasmids can E. coli carry?
How many different types of E. coli plasmids are there?
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?
1. Plasmid avoids segregational loss
2. Plasmid outcompetes other plasmids
3. 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
Harrison et al. 2012:
Which plasmid did they study in Saccharomyces? What does it contain?
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?
What is an RM system?
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
Gerdes et al., 1990:
Where is the hok/sok system located?
Which organism is it found in?
What does it do?
How does it work?
Is the plasmid selfish?
On plasmid R1
It is a post-segregational killing mechanism; one of the two daughter cells inherit it, this daughter can produce sok and will live. Other daughter without the plasmid dies because they do not have the antitoxin to hok.
Hok is a cell killing protein, sok is the antitoxin (antisense RNA of hok)
Yes, kills competitor hosts that do not possess the plasmid, more resources for its host
What are the possible benefits of transformation? List 5.
2. DNA repair
3. Sex and recombination
4. Gather new, locally-adapted alleles from the pan-genome
5. Gene loss
How can gene loss be achieved from transformation?
Recombine flanking markers that lack content, can streamline the genome = faster replication and loss of expensive protein synthesis.
What is a cost of transformation?
Could uptake damaged DNA or selfish elements.
Where does the DNA come from in transformation? List 3.
1. Dead cells, DNA may be faulty
2. Selfish elements
3. Cooperation from clonal relatives who have released DNA into the environment