Genetic recombination in bacteria .pptx

Transduction, transformation in bacteria

1. INTRODUCTION

» Genetic recombination is the process by which “Exchange of genes between
two DNA molecules to form new combinations of genes on a chromosome.

In bacteria genetic recombination can happen three ways;
1, Conjugation

2, Transformation

3. Transduction

2. 1.Conjugation

» Transfer of genetic material from one bacteria to another bacteria by physical
contact is called conjugation.

» Bacterial conjugation is the transfer of genetic material (plasmid) between
bacterial cells by direct cell-to-cell contact or by a bridge-like connection
between two cells,

» Bacterial conjugation are discovered by “Joshua Lederberg and Edward
Tatum” in 1946,

4. Fplasmid Conjugation pilus Chromosome

© Donor cell attaches to a recipient
cell with its pilus. The pilus
draws the cells together.

Fr cell — | — Fell

O

© The cells contact one another.

| © One strand of plasmid DNA
transfers to the recipient.
© —

| © The recipient synthesizes a
complementary strand to become
O O an F* cell; the donor synthesizes
a complementary strand,

A E da)

5. 2. Transformation

» Genetic recombination in which a DNA fragment from a dead_degraded
bacterium enters a competent recipient bacterium and it is exchanged for
a piece of the recipient's DNA.

» The phenomenon of transformation was first recorded by Griffith (1928).
» First time demonstrated this phenomenon in streptococcus pneumoniae.

6. Hypothesis: Material in dead bacterial cells can transform living bacterial cells

Method:

=a =
co yo
(ve) ve

\

Living Living
$ strain R strain
(virulent) (non-virulent)

Results: | |
br AMA

Mouse lives
No § strain

Mouse dies
Hae livina & atain

Dead Mix:
§ strain Living R strain
(heated) Dead $ strain

J J
a ww

Mouse dies
Has living § strain

Mouse lives
Na livina © strain

7. » Transformation involves four steps;
» Step 1. Adonor bacterium dies and is degraded.

8. Step 2

» Afragment of DNA from the dead donor bacterium binds to DNA binding
proteins on the cell wall of a competent, living recipient bacterium

9. Step 3

» The Rec A protein promotes genetic exchange between a fragment of the
donor's DNA and the recipient's DNA.

10. Step 4

» Exchange is complete,

11. 3. Transduction

» Genetic recombination in which a DNA fragment is transferred from one
bacterium to another by a bacteriophage.

» Transduction in bacteria are discovered by Lederberg and Zinder in 1951.
» Two types of transduction occurs in bacteria;

+ Generalized transduction,

+ specialized transduction,

12. Generalized transduction

+ À 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.

» There are seven steps of generalized transduction;
- 1. lytic bacteriophage adsorbs to a susceptible bacterium,

Ry

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

» 3. Abacteriophage head or capsid assembles around a fragment of donor
bacterium's nucleoid or around a plasmid instead of a phage genome by

mistake.
u
y

14. a | a
» 4, The bacteriophages are released,

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

recipient bacterium

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

» 7. The donor bacterium's DNA is exchanged tor some ot the recipient's
DNA.

16. specialized transduction

» ADNA fragment is transferred from one bacterium to another i a
temperate bacteriophage that is now carrying donor bacterial DNA due
to an error in spontaneous induction during the lysogenic life cycle.

» There are sex steps for specialized transduction:

» 1. A temperate bacteriophage adsorbs to a susceptible bacterium and
injects perla ™ ,

17. » 2, The bacteriophage inserts its genome into the bacterium's nucleoid to
become a prophage,

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,

_

18. » 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,

oe ca OA
» 5. The bacteriophage adsorbs to a recipient bacterium and injects its

genome,

oo ER

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