Mim Lecture 18

Front 1

18.1

2 types of transduction

Back 1

1) generalized (aka random) - generalized particles are formed during the lytic infection

2) specialized - require lysogeny

Front 2

18.2

generalized transduction (process)

Back 2

- virus infect the cell
- makes parts
- assembled parts leave the cell, go out into the environment and go on to infect another bacteria
0 sometimes, when the virus is making its parts, a mistake is made in the packaging. Viral particle can sometimes pack a fragment of the bacterial chromosome -> in any particular cell, you can produce a mixture of particles: viruses and transducing phage particles.

Front 3

18.3

transducing phage particle

Back 3

- a bacterial genome is incorporated into a phage particle
- has the ability to infect other bacteria and transfer its genes for recombination
- occurs in generalized transduction
- only a few particles in the cell have bacterial DNA in them)

Front 4

18.4

specialized transduction

Back 4

- viral genome enter the lysogenic cycle of infection as a prophage
- viral genome incorporated into the bacterial genome at specific sequences.
- can lay dormant for a while
- during the onset of the lytic cycle, prophage can be excised back out of the bacterial chromosome by a phage protein called XIS (named for excision)
- lytic cycle is now occurring and viral particles are made

Front 5

18.5

XIS

Back 5

- in the specialized transduction
- protein that recognizes certain sequences and correctly clips out of the viral DNA
- once in awhile, will make a mistake and instead of excising the viral chromosomal DNA precisely -> end up with a viral chromosome plus a bit of the bacterial DNA sequence.

Front 6

18.6

specialized transducing phage particle

Back 6

- if XIS makes a mistake, the excised fragment is treated as a viral chromosome, but it contains a bit of the bacterial genome.
- it will get duplicated so every particle that is made in that cell is going to be a specialized transducing phage particle.

Front 7

18.7

DNase

Back 7

- virulence factor that helps viruses avoid immune surveillance

Front 8

18.8

conjugation

Back 8

- third form of transfer
- unidirectional transfer

Front 9

18.9

F+

Back 9

- in conjugation, the bacteria that could transfer are F+
- had a plasmid in them (F plasmid)

Front 10

18.10

F-

Back 10

- in conjugation, the bacteria that oculd not transfer are F-

Front 11

18.11

F

Back 11

- fertility factor

Front 12

18.12

F pilus

Back 12

- donor F+ cells create an F pilus that binds to a receptor on the recipient (F-) bacteria.
- F pilus retract so the 2 cells are close together, and DNA transfer may occur b/w the cell-cell contacts.
- Gram negative bacteria

Front 13

18.13

phermoones

Back 13

- in gram positive cells, a pilus is NOT formed. instead attraction is achieved through the release of pheromones by the cell that does not have the plasmid
- it attract bacteria that do have plasmids

Front 14

18.14

entry exclusion

Back 14

- an F+ cell does not mate with another F+ cell
- if a cell has a particular type of plasmid, proteins from the plasmid will block the receptors that would allow the plasmid to be transferred into it again -> cells will not have multiple copies of the same plasmid

Front 15

18.15

restriction enzymes

Back 15

- in a cell with restriction enzymes, you will always have a corresponding modification enzyme that allows the restriction enzyme to recognize host DNA as 'self' so the restriction enzyme does not cut host genes

Front 16

18.16

bacteriocin

Back 16

- makes proteins that restrict the growth of other bacteria from the same species that do not have that protein
- proteins produced by plasmids that kill similar bacteria that lack same plasmid.

Front 17

18.17

transposable elements:

Back 17

insertion sequences that allow plasmid to become integrated into chromosome
- jumping genes that can move locations within the gene

Front 18

18.18

two origin of DNA replication

Back 18

- oriV and OriT

oriV: chromosomal duplication within the cell
oriT: used during transfer of the plasmid from one cell to another.

Front 19

18.19

two types of plasmids

Back 19

- conjugative and nonconjugative

- smaller plasmids (multicopy plasmids) are usually non-conjugative: 10-30 genes
- larger conjugative plasmids (low copy number plasmids) have all the genes required to make the conjugative apparatus necessary for transfer, have 30-100 genes

Front 20

18.20

mobilization

Back 20

- nonconjugative plasmids can be transferred via conjugative method if they are in a cell with a F plasmid (plasmids that can transfer themselves)

Front 21

18.21

type IV secretion system

Back 21

- what forms at the cell surface when the cells comes together.
- these systems form a channel through which various products can be secreted through the inner and outer membrane

Front 22

18.22

mating pair stabilization (MPS)

Back 22

- genes that stabilize connection between bacterai

Front 23

18.23

control genes

Back 23

- control the expression of other genes

Front 24

18.24

DNA transfer

Back 24

- genes control the gene products required for transfer of plasmid genome

Front 25

18.25

surface exclusion proteins

Back 25

- keep other F+ cells from mating with other F+ cells

Front 26

18.26

how conjugative occurs (when F+ and F- cells come together)

Back 26

- cell to cell contact made, bia pilus
- a cut is made at oriT in the F plasmid of the F+ cell (aka donor cell)
- one strand starts to be transferred to the F- (receipient cell) it begins to duplicate the strand to create a complementary strand.
- donor cell also forms a complementary strand for the DNA strand that is gives away.
- replication process called rolling circle replication
- cells separate

- at the ed of the process: 2 F+ cells.

Front 27

18.27

Hfr

Back 27

- high frequency of recombination or transfer
- use the F plasmid to create this type of cell
- transposable elements exist in plasmids that have counterparts in the bacterial chromosome allowing for homologous recombination so that plasmids may integrate into the host genome.
- an additive process

Front 28

18.28

Hfr and F- cross:

Back 28

- bacterial chromosome transfer, not a plasmid transfer
- Hfr cell acts as the donor cell to the F- recipient cell
- complete transfer of DNA qould take a long time -> so only a portion of the chromosome is transferred.
- once that portion is in the F- cell, recombination can occur if homologous sites exist between donor and recipient DNA.
- at the end: we have Hfr cell and F-
- don't see a change in cell types because we are not transferring an F plasmid, we are transferring bacterial chromosomes that have the plasmid or parts of the plasmids integrated into it.

Front 29

18.30

direction of transfer for Hfr

Back 29

- always the same
- different strains of Hfr cells may have different directions (clockwise or counterclockwise)
- but the order within that strain is the same and will not change

Front 30

18.31

F' plasmid

Back 30

- occurrence is rare since Hfr cells are not that common
- when a F+ cell integrates the plasmid into its chromosome it becomes an Hfr and when that F plasmid is correctly removed the cell reverts back to an F+ cell.
- when the F plasmid is incorrectly removed (some of the bacterial chromosome is removed along with the plasmid), the cell becomes an F' cell

F'(pro, lac) x F- = 2F'