3 DD Bacterial Genetic Variation, Gene Transfer and Virulence Flashcards Preview

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Flashcards in 3 DD Bacterial Genetic Variation, Gene Transfer and Virulence Deck (17):
1

3 mechanisms of genetic variation w/in bacterial species

1. Spontaneous mutation
2. Recombination
3. Acquisition of New DNA segments

= genetic diversity

2

Are bacterial spontaneous mutations beneficial, neutral, or deleterious for themselves?

typically deleterious

- rarely does mutation confer selective advantage (antibiotic resistance)

3

2 Types of Recombination

Antigenic variation

Genetic exchange between related organisms

4

Example of antigenic variation

Recombinational exchange between expressed and non-expressed pilin genes → new pilin gene at the expression site → new antigenetically distinct pili with new unique antigenic properties

H1 ←→ H2

5

Acquisition of New DNA Segments

Acquiring new genes via lateral transfer from other bacteria

-can alter:
virulence potential
survival characteristics
antimicrobial resistence

6

Transposons

segment of DNA (possibly encoding antibiotic resistance) contained within a bacterial or phage chromosome, or within a plasmid

7

Insertion sequence (IS)

encodes for transposase to mediate movement of transposons

8

What are Plasmids and how are they acquired?

Circular, extrachromosomal, self replicating DNA transferred from one bacterium to another via conjugation or transduction

- can confer selective advantage: carry genes for antibiotic resistance

9

Pathogenicity islands (PIs)

Large segments of DNA present in some chromosomes that are not of bacterial strain

- can contribute to virulence

10

Transformation

Naked DNA (from lysed cells; plasmids or chromosome fragments) is taken up by competent bacteria

11

Transduction

Gene transfer mediated by bacteriophage.

12

Conjugation

Genetic transfer that is dependent on physical contact between the donor and recipient cells; generally mediated by plasmids.

13

Development from Latent to Lytic states

Latent (active synthesis)
- Bacterial viruses injected into the nucleic acid of the bacterial cell → replicated → transcribed → translated.

Lytic: (viral progeny assembled)
after synthesis → components and viral progeny are assembled → cell is lysed → released.

14

Lysogenic state

(phage DNA maintained in viable host cell (prophage) and remains non-infectious → aka prophage → encodes for phage gene repressor

15

Describe how errors in bacteriophage development can lead to phage-mediated gene transfer.

Occasionally, the phage will insert a "headful"-sized piece of BACTERIAL DNA into a maturing phage capsid in place of a normal PHAGE DNA molecule → attach to other host cell → inject bacterial DNA → produce genetic recombinant or "transductant"

16

transductant

cell which has acquired new character via transfer of genetic material

aka "genetic recombinant"

17

lysogenic conversion

temperate bacteriophages start encoding genes controlling lysogenic state

- found only as a component of the phage genome, not normal bacterial genome