Bacterial genetics, mobile elements and evolution Flashcards
1
Q
What is HGT?
A
- horizontal gene transfer
- the movement and rearranging of DNA - prokaryotes e.g. bacteria
2
Q
What % of some bacterial genomes can be derived from HGT?
A
- 25%
- generaates phenomenal diversity, where selection pressure is strong e.g. antibiotics
3
Q
How many genes does an E.coli have?
A
- 5,000
- but genome size can vary in E.coli from 4,000-6,000
4
Q
How might bacteria survive, amplify and persist?
A
- results from aquisition of genes that evolved in an environment remote from humans and animals
5
Q
What are the sources of AMR?
A
- food
- some bacteria have intrinsic resistance
- wildlife
6
Q
How do bacteria generate diversity?
A
- genome reduction
- intracellular bacterium
- obligate intracellular
- endosymbiote
- gene aquisition via HGT
- normally catalyst
- extracellular pathogens
- faculative
- mutations and rearrangements
7
Q
What are the different genomes?
A
- core genome - should stay the same
- accessory genome - variable - 1500 genes that can change strain by strain
- e.g. E.coli - pathogenic has more genes
8
Q
What is the MGE?
A
- mobile genetic elements - type of DNA that can move around within the genome
- transposons
- retrosposons
- DNA transposons
- insertion sequences
- plasmids
- bacteriophage
- group II introns
- group I introns
- total of all MGEs in a genome - mobilome
9
Q
What is the clinical importance of gene transfer?
A
- a plasmid = circular DNA that is self-replicating,located outside of chromosome, contains resistance mechanisms (EBSL) that can be transferred via pilus (adhere to other bacterium)
10
Q
What is HGT/LGT?
A
- where DNA is physically transferred from one cell to another
- without the absolute requirement for cell division
- and the incorporation of that DNA into the cells genome so that it is stably inherited
11
Q
What are HGTs 2 independent processes?
A
- physical movement of DNA
- incorporation of DNA into the new cells genome
- cant cope with new energy requirements - so back to normal after a few generations
- can occur across species
12
Q
What are the 3 mechanisms of gene transfer?
A
- conjugation - direct contact
- transformation - a bacterium dies and its DNA is released into enviro and taken up
- transduction - a phage takes some DNA and transfers it to another bacterium
13
Q
How does conjugation work?
A
- involves plasmids and conjugative pilli
- close contact
- normally between closely related strains or species
- donor needs to be able to produce conjugative pilli
- most important method
14
Q
Relationship between plasmids and bacterial fitness?
A
- plasmids slow down growth/ less fit
- but stay in the animal longer
15
Q
How does transformation occur?
A
- uptake of free DNA by competent bacteria
- competence = physiological state - dependent on enviro - ability to uptake macromolecules that bind to its surface
- does not require close contact
- from dead bacteria