Bacterial Genetic Variation, Gene Transfer and Evolution of Virulence Flashcards
Regulation of gene expression can occur in two steps.What are they?
- Regulation of transcription
2. Control of transcription by DNA rearrangement
Give an example of regulation of transcription in bacteria.
Bacteria do not express virulence factors in high iron environments. Iron is low in the animal hosts.
When iron gets low virulence genes are expressed.
Salmonella typhimurium can control transcription by DNA rearrangement what two genes does it commonly switch?
Switching in the synthesis of two alternative flagellar antigens (H1 and H2)
Neisseria gonorrhoeae can control transcription by DNA rearrangement what two genes does it commonly switch?
Alteration between several antigenic forms of pili expressed on the cell surface.
What kind of mutation is characterized by small changes to the DNA at a very low rate that can increase resistance to antimicrobials and increase likelihood of invasive disease?
Spontaneous mutations
What type of mutation is characterized by switching of genes?
Recombination
What are transposons?
DNA that can move themselves to new locations.
They cannot self replicate
They do not require extensive homology or host recombination machinery
What is insertion sequence?
Transposons that simply encode “transposase”
They turn off genes in which they transpose
They turn on genes in which they are adjacent
What is a complex sequence?
Carry additional genes such as resistance to antimicrobials or toxins
What is bacteriophage conversion?
Uninfected bacteria do not express virulence factor, but infected bacteria do.
Virulence gene is carried by the bacteriophage.
What is a plasmid?
Autonomously replicating, usually circular, extrachromosomal DNA’s ranging in size
What are “Pathogenicity Islands”?
Large segments of DNA
Not all of the strain will have them
May be transmitted by viruses
What did the Griffith experiment of 1928 do?
Discovered transformation. Rough strain pneumococcus was able to take up naked DNA and transform to smooth strain
What is a competent bacterial cell?
A bacteria that is able to take up naked DNA, but it has to be at a certain point in the growth cycle and has to synthesize the necessary proteins
Can you induce a bacterial cell to become competent?
Yes. with calcium chloride and low temperature
What is transduction?
Gene transfer mediated by a bacteriophage
What is prophage?
A bacterial cell infected by a lysogenic virus that is not actively producing viruses
What prevents a prophage from going into the lytic cycle?
Repressor proteins
What is bacteriophage conversion?
Bacteriophage encodes gene(s) which may be expressed during the lysogenic state and cause the appearance of a new phenotypic trait
- Diphtheria toxin
- Scarlet fever toxin
What genetic information is encoded on the F plasmid?
- Autonomous replication
- Synthesis of Sex pili
- Conjugative transfer
- Ability to integrate into the bacterial chromosome
What is a oriT?
The origin of transfer
Transferred by singe strand
What is the unique characteristic of conjugative transposons?
Once they transfer into the recipient cell they are able to transpose themselves into the chromosome
Can encode resistances
