Horizontal gene transfer

Question 1

Why is acinetobacter baumannii an issue?

Answer 1

It picks up antibiotic resistance genes v easily

Question 2

Where did acinetobacter baumannii come from?

Answer 2

Wars in afghanistan and iraq

Question 3

Three mechanisms of HGT?

Answer 3

Transformation, transduction, conjugation

Question 4

What must the HGT’d gene offer the bacteria in order for that gene to become fixed within the bacteria

Answer 4

A fitness advantage

Question 5

What is conjugation?

Answer 5

Attachment between 2 cells where the DNA is exchanged

Question 6

What is transduction?

Answer 6

Phage can infect one cell, take up some of its DNA, and then transfer that DNA to another bacteria

Question 7

What is transformation?

Answer 7

Bacteria pick up DNA from the environment

Question 8

WHat happens if the new DNA is integrated into the hosts chromosome?

Answer 8

Replication leads to a population of stable recombinants

Question 9

What happens if the new DNA is self replicated, e.g. converts into a plasmid?

Answer 9

Replication leads to a population of stable recombinants

Question 10

What are the two ways that HGT’d DNA would not result in the formation of stable recombinants?

Answer 10

If the donor DNA cannot self replicate
If the host restricts the DNA–> using restriction endonucleases

Question 11

What does it mean if a bacteria is competent?

Answer 11

They are able to pick up DNA

Question 12

What does becoming competent require from a bacteria?

Answer 12

For them to stop undergoing cell division

Question 13

Griffith experiment 1928?

Answer 13

Injected a mouse with a nonvirulent strain of S. pneumonia–> lived
Injected a mouse with a virulent strain of S. pneumonia–> died
Injected a mouse with a heat-killed virulent strain of S. pneumonia–> lived
Injected a mouse with a nonvirulent strain, and a heat-killed virulent strain of S. pneumonia–> died

Question 14

Outcome of Griffiths 1928 experiment?

Answer 14

Showed that the non virulent strain took up some virulent material from the dead, virulent strain

Question 15

Example of a naturally competent bacteria?

Answer 15

Neisseria

Question 16

When do bacteria usually become competent?

Answer 16

Just before stationary phase

Question 17

How can bacteria be artificially made competent?

Answer 17

Using chemicals or physical perturbations of cell wall and cytoplasmic membrane

Question 18

First step of transformation?

Answer 18

Reversible binding of dsDNA to the surface of a bacteria via DNA binding proteins

Question 19

Which type of bacteria has more DNA binding proteins?

Answer 19

Gram +ve (100 vs 10)

Question 20

What follows binding of DNA to the binding proteins on the bacterial surface?

Answer 20

dd and ds cleavage of bound DNA by endonucleases expressed on the surface

Question 21

How large are the fragments of DNA that are cleaved on the bacterial cell surface?

Answer 21

13-18kb

Question 22

What happens after the DNA has been cleaved?

Answer 22

Enzyme makes it ssDNA

Question 23

WHat follows the DNA being made into ssDNA?

Answer 23

ssDNA is transported across the peptidoglycan and cell membranes

Question 24

What happens once the ssDNA is inside the cell?

Answer 24

it is incorporated into the genome via homologous recombination

Question 25

Efficiency diff between homologous and non-homologous recombination?

Answer 25

Homologous is 10^9 more efficient

Question 26

Where are some competence proteins localised in bacteria?

Answer 26

Could be only at the poles etc

Question 27

Possible issue for a bacteria with competence?

Answer 27

If the bacteria discovers that it has foreign DNA (e.g. in N. gonorrhoeae) then it may kill itself

Question 28

Two methods of conjugation?

Answer 28

Plasmid is transferred from cell to cell Plasmid of DNA is excised from the host chromosome and into the recipients chromosome

Question 29

How was conjugation discovered?

Answer 29

Mixed two diff types of bacteria together One type could produce AA X, Y and Z The other produces AA A, B, C They only produced colonies when together, not when separate

Question 30

What needs to be expressed for conjugation to work?

Answer 30

Transfer proteins

Question 31

What do transfer proteins do in conjugation?

Answer 31

Make a type 4 secretion system which allows the bacteria to attach to the recipient cell envelope, and transfer the plasmid

Question 32

Conjugation basic process first bit?

Answer 32

Donor join with recipient Conjugation tube forms

Question 33

What happens in conjugation after the tube forms?

Answer 33

Single stranded nick in one strand in the plasmid at the origin of transfer

Question 34

What happens after the single stranded nick in conjugaiton?

Answer 34

ssDNA is displaced into the host via rolling circle replication

Question 35

What is rolling circle replication?

Answer 35

As the strands are both replicating another copy is made on the strand that is being transferred as well as the strand that is remaining in the donor cell

Question 36

What happens after rolling circle replictation?

Answer 36

Replication of both donor and recipient plasmid DNAs continues until completion, and cells separate