Bacterial genetics, mobile elements and evolution

Question 1

What is HGT?

Answer 1

• horizontal gene transfer
• the movement and rearranging of DNA - prokaryotes e.g. bacteria

Question 2

What % of some bacterial genomes can be derived from HGT?

Answer 2

• 25%
• generaates phenomenal diversity, where selection pressure is strong e.g. antibiotics

Question 3

How many genes does an E.coli have?

Answer 3

• 5,000
• but genome size can vary in E.coli from 4,000-6,000

Question 4

How might bacteria survive, amplify and persist?

Answer 4

• results from aquisition of genes that evolved in an environment remote from humans and animals

Question 5

What are the sources of AMR?

Answer 5

• food
• some bacteria have intrinsic resistance
• wildlife

Question 6

How do bacteria generate diversity?

Answer 6

• genome reduction
  
  • intracellular bacterium
  • obligate intracellular
  • endosymbiote
• gene aquisition via HGT
  
  • normally catalyst
  • extracellular pathogens
  • faculative
• mutations and rearrangements

Question 7

What are the different genomes?

Answer 7

• 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

Question 8

What is the MGE?

Answer 8

• 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

Question 9

What is the clinical importance of gene transfer?

Answer 9

• 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)

Question 10

What is HGT/LGT?

Answer 10

• 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

Question 11

What are HGTs 2 independent processes?

Answer 11

• 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

Question 12

What are the 3 mechanisms of gene transfer?

Answer 12

• 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

Question 13

How does conjugation work?

Answer 13

• 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

Question 14

Relationship between plasmids and bacterial fitness?

Answer 14

• plasmids slow down growth/ less fit
• but stay in the animal longer

Question 15

How does transformation occur?

Answer 15

• 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

Question 16

How does transduction work?

Answer 16

• gene transfer mediated by a bacteriophage (virus specific to a bacteria)

Question 17

What is fluoroquinolone resistant to and why?

Answer 17

• single point mutation - change bacterial fitness
• resistant to E.coli, salmonella and Campylobacter