Bacterial Genetic Variation, Gene Transfer and Evolution of Virulence

Question 1

Regulation of gene expression can occur in two steps.What are they?

Answer 1

1. Regulation of transcription

2. Control of transcription by DNA rearrangement

Question 2

Give an example of regulation of transcription in bacteria.

Answer 2

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.

Question 3

Salmonella typhimurium can control transcription by DNA rearrangement what two genes does it commonly switch?

Answer 3

Switching in the synthesis of two alternative flagellar antigens (H1 and H2)

Question 4

Neisseria gonorrhoeae can control transcription by DNA rearrangement what two genes does it commonly switch?

Answer 4

Alteration between several antigenic forms of pili expressed on the cell surface.

Question 5

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?

Answer 5

Spontaneous mutations

Question 6

What type of mutation is characterized by switching of genes?

Answer 6

Recombination

Question 7

What are transposons?

Answer 7

DNA that can move themselves to new locations.

They cannot self replicate

They do not require extensive homology or host recombination machinery

Question 8

What is insertion sequence?

Answer 8

Transposons that simply encode “transposase”

They turn off genes in which they transpose

They turn on genes in which they are adjacent

Question 9

What is a complex sequence?

Answer 9

Carry additional genes such as resistance to antimicrobials or toxins

Question 10

What is bacteriophage conversion?

Answer 10

Uninfected bacteria do not express virulence factor, but infected bacteria do.

Virulence gene is carried by the bacteriophage.

Question 11

What is a plasmid?

Answer 11

Autonomously replicating, usually circular, extrachromosomal DNA’s ranging in size

Question 12

What are “Pathogenicity Islands”?

Answer 12

Large segments of DNA

Not all of the strain will have them

May be transmitted by viruses

Question 13

What did the Griffith experiment of 1928 do?

Answer 13

Discovered transformation. Rough strain pneumococcus was able to take up naked DNA and transform to smooth strain

Question 14

What is a competent bacterial cell?

Answer 14

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

Question 15

Can you induce a bacterial cell to become competent?

Answer 15

Yes. with calcium chloride and low temperature

Question 16

What is transduction?

Answer 16

Gene transfer mediated by a bacteriophage

Question 17

What is prophage?

Answer 17

A bacterial cell infected by a lysogenic virus that is not actively producing viruses

Question 18

What prevents a prophage from going into the lytic cycle?

Answer 18

Repressor proteins

Question 19

What is bacteriophage conversion?

Answer 19

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

Question 20

What genetic information is encoded on the F plasmid?

Answer 20

1. Autonomous replication
2. Synthesis of Sex pili
3. Conjugative transfer
4. Ability to integrate into the bacterial chromosome

Question 21

What is a oriT?

Answer 21

The origin of transfer

Transferred by singe strand

Question 22

What is the unique characteristic of conjugative transposons?

Answer 22

Once they transfer into the recipient cell they are able to transpose themselves into the chromosome

Can encode resistances