Bacterial Genetic Variation, Gene Transfer and Evolution of Virulence Flashcards
What does the bacterial genome consist of?
- Chromosome = DNA molecule(s) that encode genes essential for growth under “normal” conditions.
- Plasmids
- Bacterial viruses
What are the three mechanisms of genetic variation?
- Spontaneous mutation
- Recombination
- Acquisition of new DNA segments
How often do spontaneous mutations occur?
once in approx 10^8 – 10^10 organisms
Where can you see recombination?
- Either site-specific or homologous recombination within a particular organism,
- or genetic exchange and recombination between closely related organisms that results in new strains
What’s an example in bacteria of recombination?
Recombinational exchange between expressed and non-expressed pilin genes of N. gonorrhoeae can result in new pilin gene at the expression site, and therefore production of a new antigenetically distinct pili with new unique antigenic properties
What types of DNA segments can bacteria acquire?
- Transposable elements (IS elements and complex transposons)
- Bacteriophage transfer (Lysogenic conversion)
- Plasmids
- “Pathogenicity islands”
What is a transposon?
Segment of DNA contained within a bacterial or phage chromosome, or within a plasmid that has the property of being enzymatically moved from one DNA location to another
DNA that jumps places
transpose=move places
T/F: Plasmids are self-replicating while transposons are not?
True
What are pathogenicity islands?
- Large segments of DNA present in some chromosomes that are acquired from an unrelated organism
- PI appear as “insertions” when comparing the genomes of two isolates of the same species
- May contribute to virulence
Just recognize that everything we talked about contributes to virulence of bacteria
They do this by conferring some kind of antibiotic resistance or provide additional virulence factors (adhesion, toxins, survival, etc)
T/F: Spontaneous mutation occurs during replication or during natural growth are usually advantageous to bacteria?
False
- That’s why its so rare to get antibiotic resistance in one strain
- But when there is a selective advantage, mutation can persist if environment selects for it
What are mechanisms (actions) for genetic exchange between bacteria?
Transformation
Transduction
Conjugation
Which one is the genetic transfer of naked DNA strands/plasmids?
Transformation
T/F: bacteria are able to acquire naked DNA at any stage of growth cycle?
False
Many transformable species become competent for DNA uptake at only certain points in the growth cycle, and competence requires synthesis of specialized proteins to mediate the uptake
What key component is required for transfer of segments of DNA in transduction?
Bacteriophage (virus)
*you need an extra duck, or virus to do the transfer. Stupid I know… but when this question comes up on the test, you are going to think of transDUCKtion and then thank me. Duck Viruses…
What’s the difference between the lytic infection and lysogenic formation with temperate bacteriophages?
Lytic: virus lysis bacteria and spills out components
Lysogenic: host remains viable and infecting phage DNA is maintained in host genome in non-infectious state (LYSed to GENes”)
What is a prophage?
- Bacteriophage genome that is incorporated into bacterial DNA where it becomes passively replicated (lysogenic stage)
- Can lead to lytic stage. But when you hear prophage, think lysogenic.
What other material can be transferred by transduction?
Bacterial plasmids, including those which confer antibiotic resistance, may also be transferred by generalized transduction from phages
-prevalent with Gram +
What plasmid mediates conjugation?
Plasmid F (for “fertility”)
The F plasmid contains genetic information encoding what traits?
- Autonomous replication of plasma DNA
2. Synthesis of sex pili (F pili)
What’s the difference between conjugative/ non-conjugative plasmids? (it’s what you think)
Conjugative Plasmids: self-transmissible, mediate their own transfer between cells.
Non-Conjugative Plasmids: mobilizable; can be passively transferred during conjugation
What do you call the cell that is receiving the sex pilus?
F- =recipient cell
F+ = sex pilus
What can conjugative transposons do?
- mediate conjugation transfer between cells
- also can transpose into recipient genome
- Often encode antibiotic resistance, especially Tetracycline
T/F: bacteria can transfer through conjugation between both gram (+) to gram (-), and also gram (-) to plants and fungi?
True
LO: Describe how errors in bacteriophage development can lead to phage-mediated gene transfer.
- During phage assembly, it can accidentally insert bacteria DNA instead of phage DNA into capsized
- It can still attach to new host and inject its bacterial DNA
- Bacterial DNA then recombines in recipient genome to produce a transductant
LO: Define lysogenic conversion, and how its different from normal transduction.
- During lysogenic state, temperate phage DNA may be expressed in host cells causing appearance of new phenotypic trait in lysogenic host.
- These genes are found only as a component of the phage genome (where as, generalized transduction is of normal bacterial genome).
