3 DD Bacterial Genetic Variation, Gene Transfer and Virulence Flashcards
3 mechanisms of genetic variation w/in bacterial species
- Spontaneous mutation
- Recombination
- Acquisition of New DNA segments
= genetic diversity
Are bacterial spontaneous mutations beneficial, neutral, or deleterious for themselves?
typically deleterious
- rarely does mutation confer selective advantage (antibiotic resistance)
2 Types of Recombination
Antigenic variation
Genetic exchange between related organisms
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
Acquisition of New DNA Segments
Acquiring new genes via lateral transfer from other bacteria
-can alter:
virulence potential
survival characteristics
antimicrobial resistence
Transposons
segment of DNA (possibly encoding antibiotic resistance) contained within a bacterial or phage chromosome, or within a plasmid
Insertion sequence (IS)
encodes for transposase to mediate movement of transposons
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
Pathogenicity islands (PIs)
Large segments of DNA present in some chromosomes that are not of bacterial strain
- can contribute to virulence
Transformation
Naked DNA (from lysed cells; plasmids or chromosome fragments) is taken up by competent bacteria
Transduction
Gene transfer mediated by bacteriophage.
Conjugation
Genetic transfer that is dependent on physical contact between the donor and recipient cells; generally mediated by plasmids.
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.
Lysogenic state
(phage DNA maintained in viable host cell (prophage) and remains non-infectious → aka prophage → encodes for phage gene repressor
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”
