Bacterial Genetic Variation Flashcards
When are virulence genes in bacteria often expressed?
Low iron conditions
the environment is high iron. The cell, tho? Low iron. Perfect time to display infectious genes
What is phase variation?
What are examples of this?
the control of transcription of DNA variation
In Salmonella, rapid reversible switching in synthesis of two flagellar antigen. (molecular switch=invertible segment of DNA)
In gonorrhea, alternation between several antigenic forms of pili on cell curface.
How often does spontaneous mutation occur in bacteria? What is its significance?
Spontaneous mutation = single base changes, deletions and/or insertions
10^-6,-10^-10
These are important for drug resistance - method of developing resistance in pseudomonas + tuberculosis
What is bacterial recombination?
Site specific or homologous recombination within an organism or between closely related organisms
Transposons
A discrete segment of DNA which is capable of moving itself (or a copy) from one chromosomal location to another.
Not self-replicating, can be incorporated into a cell as part of transposon/bacteriophage/plasmid
Insertion Sequence
Transposons that encose transposase. Inactivate the genes they transpose and turn ON expression of adjacent genes.
Complex transposons
carry additional genes, such as those that encode for antibiotic resistance, toxins, adhesins and other virulence factors.
Bacteriophage conversion
certain virulence genes are not “normal” component of genome
these babies are virulence factors that were carried and expressed by bacterial strains that have become lysogenic
found in diphtheria, cholera, and botulism! yay!
Plasmids
autonomously replicating, circular extrachromosomal DNA.
can be transferred from one bacterium to another via conjugation or translocation.
often virulence factors/antibiotic resistance
Pathogenicity Islands
large segments of DNA that encode for virulence. W/o these islands, bacteria often aren’t pathogenic!
Transformation
Mechanism of genetic exchange between bacteria
Naked DNA (probs from lysing cells) incorporated into bacterial DNA
transformable species are competent for DNA uptake at certain stages of life cycle - some can be induced w/ CaCl2 and decreased temp
Transduction
gene transfer mediated by bacteriophage (bacterial virus!)
- ) Virulent bacteriophages exist b/c virus attaches to bacteria, injects its nucleic acids, viral genome replicated, and progeny released upon cell lysis
- ) However! Temperate phages don’t kill their host. May cause lytic/lysogenic response.
Lytic Reponse
phage multiplication and lysis
Lysogenic response
infecting DNA maintained by host in non-infectious stage called a prophage. (maintained by prophage encoded repressor protein)
Under stress, this prophage may convert into a lytic bacteriophage!
How are transducing DNA phages formed?
Mostly through errors in DNA packaging during phage assembly. Some phages accidentally put some bacterial DNA into their package.
