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
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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
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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
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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
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5
Q

What are the sources of AMR?

A
  • food
  • some bacteria have intrinsic resistance
  • wildlife
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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
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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
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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
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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)
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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
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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
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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
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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
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14
Q

Relationship between plasmids and bacterial fitness?

A
  • plasmids slow down growth/ less fit
  • but stay in the animal longer
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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
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16
Q

How does transduction work?

A
  • gene transfer mediated by a bacteriophage (virus specific to a bacteria)
17
Q

What is fluoroquinolone resistant to and why?

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