Microbial Genetics

Question 1

How do bacteria gain extra genetic material?

Answer 1

NOT through binary fission! Through transformation (absorbing extracellular DNA from lysed bacteria), conjugation (bacterial “sex”), or transduction (DNA phage infects bacterial cell w/some other bacteria DNA)

Question 2

What is an episome?

Answer 2

A plasmid which has been integrated into bacterial chromosome

Question 3

What kinds of genetic material are in bacteria?

Answer 3

Bacterial chromosome
Plasmids
Bacterial phages

Question 4

Lytic phage?

Answer 4

Infects bacteria, lyses bacteria, and goes to infect more bacteria

Question 5

Temperate phage?

Answer 5

Stably integrates DNA into host cell DNA

Question 6

What is homologous recombination?

Answer 6

An exchange of genes between different pieces of DNA
Linear DNA which shares homology with bacterial chromosome can get switched out
Requires a recombination protein (rec A most common)
Linear DNA broken down by exonucleases (linear DNA not stable in bacteria)
Incorporated DNA becomes permanent part of cell’s genome

Question 7

Tell me about transformation

Answer 7

Uptake of “naked” DNA
If some regions are homologous with the bacteria’s own chromosome, it’ll try it on through HR
i.e. non-encapsulated strep pneumo strains can be transformed to encapsulated strep pneumo

Question 8

Tell me about conjugation

Answer 8

Genes transferred through cell-to-cell contact
ssDNA transferred from donor cell to recipient cell
Plasmids are circular and are stable without HR, chromosomal DNA transfer needs to be stabilized by HR

Question 9

What are fertility factors (relating to conjugation?)

Answer 9

They supply all the needed components (i.e. sex pili, which establishes bridge between two bacterium)
Two things to know:
oriT - origin of transfer - ssbreak occurs here to initiate transfer of DNA to another bacterium
tra operon - enxodes sex pili and other proteins needed for conjugation

Question 10

Bacterial mating types

Answer 10

F- are recipient cells; no F factor
F+ are donors; they can initiate conjugation
Hfr is high frequency recombinant - donor with F factor integrated into its own chromosome

In every “cross,” one cell MUST be F-; no homosexuals here

Question 11

What is oriT?

Answer 11

Origin of transfer

Where the plasmid unwinds and enters “female” cell during conjugation

Question 12

Important things about Hfr x F- conjugal cross

Answer 12

Can only send a part of the genome - rarely sends full thing
Bacteria needs to stabilize linear DNA through HR quickly - before degrades linear DNA
Rarely causes “sex change,” because not all fertility factor transferred

Question 13

Tell me about transduction

Answer 13

Transfer of bacterial DNA to another bacterium through phage vector; virulent phage or temperate phage

Question 14

Generalized transduction

Answer 14

Lytic phage mistakenly incorporates bacterial chromosomal DNA into phage head
When that phage infects another bacterium, that bacterial DNA can be utilized by teh other bacterium if it is stabilized by HR

Question 15

Specialized transduction

Answer 15

Temperate phages can remove bacterial genes when the phage gets ready to replicate its DNA
Excised bacterial DNA can be transferred to a new bacteria
ONLY BACTERIA GENES CLOSE TO PHAGE INSERTION CAN BE EXCISED
Transferred bacterial genes must be stabilized by HR

Question 16

So, recap: which types of phages use generalized and which type use specialized transduction?

Answer 16

General: Lytic phages
Specialized: Temperate phages

Question 17

What is lysogenic conversion?

Answer 17

When bacteria gain a new trait, such as ability to produce toxin:

Question 18

What are the examples of lysogenic conversion?

Answer 18

Cholera toxin - cholera
Botulinum toxin - botulism
Exotoxins A-C - strep pyogenes - causes many diseases
Diphtheria toxin - diptheria
Shiga toxin - shigellosis

Question 19

Review summary chart - slide #20

Answer 19

Sweet!

Question 20

Intrinsic resistance

Answer 20

A resistance CAN NOT be tranferred between bacteria;
Usually structural or physiological
i.e. bacteria that doesn’t produce peptidoglycan resistant to penicillin

Question 21

Chromosome-mediated resistance

Answer 21

Bacterial chromosome genes encode a particular form of resistance
Genetic - can be transferred
Usually modify binding target so drug can’t bind

Question 22

Plasmid-mediated resistance

Answer 22

Resistance gene located on plasmid
Usually degrade, modify, or pump drug out of cell
Plasmid transfer occurs between bacteria species,

Question 23

Which mechanism is responsible for multi-drug resistant bacteria?

Answer 23

Plasmid mediated resistance

Question 24

What is the difference between an R factor and F factor?

Answer 24

R factor - resistance factor - encodes fertility factor + resistance genes

Question 25

Resistance determinant?

Answer 25

The genes for drug resistance; this part of the plasmid has “hot spots” (insertional sequences) for transposon to help create multi-drug resistant plasmids

Question 26

How do you create a multi-drug resistant plasmid?

Answer 26

Collect a lot of “cassettes”

Question 27

What is the role of an integron in multi-drug resistance?

Answer 27

The integron is a 3 component system that captures and disseminates genes
found in plasmids, chromosomes, transposons

Question 28

Transposons

Answer 28

Jumping genes
Mobile DNA elements that transfer themselves/copy themselves from one DNA molecule to another
Contains indirect repeats on each end