Horizontal gene transfer 2 Flashcards
Where was colistin resistance first found?
On a transposable element
What is a transposable element?
A piece of DNA that is able to move around the genome
Why did the collisting resistance genes remain stable in the plasmid?
The IS elements that allowed transposable elements to move were lost over time
What are conjugative transposons (ICE elements)
Bits of DNA that move via conjugation, and can move around the chromosome
What do ICE elements contain?
Antibiotic resistance genes, transfer genes
How are ICE elements transferred?
Excise itself from the chromosome to make a plasmid
Generates an attachment to another bacteria cell
ss nick
transferred via rolling circle replicaiton
Inserted into the recipients chromosome
What can conjugation do to transformation?
Inhibit it
How can conjugation inhibit transformation?
The ICE elements had a sequence that coded a DNase–> degraded environmental DNA
Why would conjugation inhibit transformation?
Prevents competition from DNA that would otherwise be taken up by transformation
Two modes of transduciton?
Generalised transduction, specialised transduction
What is generalised transduction?
DNA from any portion of the host genome is packaged inside the virion
What is specialised transduction?
DNA from a specific region of the host chromosome is integrated directly into the virus genome
What are phages capable of transduction known as?
Transducing phage
How does the lytic phage cycle lead to transducing phages being formed?
After making new phages using the hosts machinery, some of the new phage may accidentally contain the host chromosomal DNA instead of the phage DNA–> these phages can pass this bacterial DNA on
Why does transduction only happen in closely related donors and recipients?
The donor and recipient must have the same surface proteins that the phage can recognise
How can HGT’d genes ensure the recipient keeps them?
They may contain antitoxin genes in their sequence, meaning if the host removes them the host will die from the toxin
Barriers to HGT?
Foreign DNA is usually degraded
Foreign DNA must be expressed to be useful
How is foreign DNA degraded?
Restriction modification systems, DNases, CRISPR
Why may foreign DNA not be expressed?
e.g. H-NS protein silences expression of genes w/ lower %GC content than the host chromosome
