bacterial transduction

1

Transduction

BY: Vikas Kumar

Contents• Historical

• Transduction

• Mechanism • Bacteriophages and its life cycles

• Type of transduction• Generalized Transduction

• Specialized Transduction

• Significance 2

3

historicalLederberg & Zinder• Transduction was first discovered in 1952 by Joshua

Lederberg and Norton Zinder

Joshua Lederberg Norton Zinder

How transduction was discovered

4

• Studied in Salmonella typhimurium

• Plated two auxotrophic strains (LA-2 and LA-22) individually on minimal medium, no cells grew.

• Plated a mixture of the two auxotrophic strains on minimal medium, cells grew into colonies.

• Thus, genetic exchange was taking place between the two cell types.

•

Unexpected discovery

U-tube Experiment

• Performed U-tube experiment .

• Found that part of the cells on one side of the U-tube were prototrophs (could

grow in minimal medium).

5

U-tube Experiment

6

Transduction

Definition - Unlike transformation in which the naked DNA is transferred in transduction DNA is carried by a bacteriophage.

or

In transduction, DNA is transferred from cell to cell through the agency of viruses

NOTE :- All phages can be transducer and not all bacteria are transducible

7

Transduction has been found to occur in a variety

of prokaryotes, including certain species of the

Bacteria: Desulfovibrio, Escherichia,

Pseudomonas, Rhodococcus, Rhodobacter,

Salmonella, Staphylococcus, and Xanthobacter, as

well as Methanobacterium thermoautotrophicum.

EXAMPLES OF BACTERIA

8

9

Mechanism of Transduction

Bacteriphage

• Firstly Descovered in 1915 by Fredrick Twort and two years later by

Felix d’Herelle.

• Means bacteria eater.

• A virus that infects certain type of bacteria and replicates within them

Types of bacterio-phage

Virulent: capable of causing infection and eventually destruction and death of the bacterial cell. These follow the lytic cycle. e.g. T4 host E.coli.

Temperate: does not cause destruptic infection instead phage DNA is incorporated into bacterium DNA and is replicated with it and after some cycle become virulent cause lysis.

• e.g. lambda phage.10

Life cycle of bacteriophage

11

Transduction

• There are two types of transduction:

– Generalized transduction: A DNA

fragment is transferred from one bacterium

to another by a lytic bacteriophage that is

now carrying donor bacterial DNA due to an

error in maturation during the lytic life cycle.

12

Generalised Transduction

13

1. A lytic bacteriophage adsorbs to a susceptible bacterium.

2. The bacteriophage genome enters the bacterium. The genome directs the bacterium's metabolic machinery to manufacture bacteriophage components and enzymes

14

3. Occasionally, a bacteriophage head or capsid assembles around a fragment of donor bacterium's nucleoid instead of a phage genome by mistake.

steps in Generalised Transduction (cont’d)

4. The bacteriophages are released.

steps in Generalised Transduction (cont’d)

15

5. The bacteriophage carrying the donor bacterium's DNA adsorbs to a recipient bacterium

6. The bacteriophage inserts the donor bacterium's DNA it is carrying into the recipient bacterium .

16

steps in Generalised Transduction (contd)

7. The donor bacterium's DNA is exchanged for some of the recipient's DNA.

• Specialized transduction:• A DNA fragment is transferred from one

bacterium to another by a temperate

bacteriophage that is now carrying

donor bacterial DNA due to an error in

spontaneous induction during the

lysogenic life cycle.• In specialized transduction the phage

inserts its genome at the specific site.

17

Specialised Transduction

18

1. A temperate bacteriophage adsorbs to a susceptible bacterium and injects its genome .

2. The bacteriophage inserts its genome into the bacterium's nucleoid to become a prophage.

Steps in Specialised Transduction (cont’d)

19

3. Occasionally during spontaneous induction, a small piece of the donor bacterium's DNA is picked up as part of the phage's genome in place of some of the phage DNA which remains in the bacterium's nucleoid.

4. As the bacteriophage replicates, the segment of bacterial DNA replicates as part of the phage's genome. Every phage now carries that segment of bacterial DNA.

Steps in Specialised Transduction (cont’d)

20

5. The bacteriophage adsorbs to a recipient bacterium and injects its genome.

6. The bacteriophage genome carrying the donor bacterial DNA inserts into the recipient bacterium's nucleoid.

Significance of transduction

• It transfers genetic material from one bacterial cell to another and alter the genetic characteristics.

• For example: In specialised transduction the gal gene, a cell lacking ability to metabolize galactose could aquire the ability .

• It shows the evolutionary relationship between the prophage and host bacterial cell.

• Prophage can exist in a cell for a long period suggests a similar possible mechanism for the viral origin of cancer.

• It provides a way to study the gene linkage.

21

THANKS

22