Transduction, a process in microbial genetics........

1. TRANSDUCTION
Prepared and presented by:
Mahesh Lamsal
Central Dept.of Biotechnology,kirtipur
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INCLUDES:
1.History
2.Introduction to transduction
3.Life cycle of bacteriophage
4.Types of transduction
a.Generalised transduction
b.Specialised transduction
5.Significance

2. History:
Transduction was first discovered by
Norton Zinder and Joshua Lederberg in 1952.
Joshua LederbergNorton Zinder
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3. How transduction was discovered
• 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.
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U-tube Experiment

5. Transduction
Definition: Gene transfer from a donor to a recipient by way of a bacteriophage.
Unlike transformation in which the naked DNA is transferred in transduction DNA is carried by a
bacteriophage.
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.
NOTE : All phages can be transducer and not all bacteria are transducible
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6. • Transduction happens through either the lytic cycle or
the lysogenic cycle.
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7. Life cycle of bacteriophage
Lytic or virulent
• Phage that multiply within the host cell, lyse the cell and release
progeny phage (e.g. T4)
Lysogenic or temperate phage
• Phage that can either multiply via the lytic cycle or enter a quiescent
state in the bacterial cell.
• Expression of most phage genes repressed
• Prophage – Phage DNA in the quiescent state
• Lysogen – Bacteria harboring a prophage
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9. Lytic cycle of bacteriophage
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10. Types of transduction
1. Generalized -Transduction in which potentially
any donor bacterial gene can be transferred.
2. Specialized- Transduction in which only certain
donor genes can be transferred
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11. General steps of Transduction
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1.Attachment/Adsorption of bacteriophage to the bacteria
2.Penetration of phage DNA
3.Replication of phage DNA/RNA
4.Synthesis of nucleic acid and proteins
5.Assembly of phage protein and nucleic acid
6.Release of mature bacteriophage

12. 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.
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13. Steps involved in generalised transduction;
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
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14. 3. Occasionally, a bacteriophage head or capsid assembles
around a fragment of donor bacterium's nucleoid instead of a
phage genome by mistake
4. The bacteriophages are released.
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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
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16. 7. The donor bacterium's DNA is exchanged for some of the
recipient's DNA.
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18. Specialised transduction:
• Lambda is a good example of a specialized transducing phage. As
a prophage, λ always inserts between the gal region and
the bio region of the host chromosome. In transduction experiments,
λ can transduce only the galand bio genes.
• 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.
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19. Specialised transduction:
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20. Steps involved in specialised transduction
1. A temperate bacteriophage adsorbs to a susceptible
bacterium and injects its genome .
The bacteriophage inserts its genome into the bacterium's
nucleoid to become a prophage.
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21. 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.
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.
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22. The bacteriophage adsorbs to a recipient bacterium and injects
its genome.
The bacteriophage genome carrying the donor bacterial DNA
inserts into the recipient bacterium's nucleoid.
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23. Video for generalised transduction
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24. Video for specialised transduction
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25. Other types of transduction include:
1. Co-transduction: Generalized transduction can be used to
derive linkage information about bacterial genes in cases in which
genes are close enough that the phage can pick them up and transduce
them as a single piece of DNA, an outcome known as cotransduction.
2. Abortive transduction:
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26. Significance of transduction
• It transfers genetic material from one bacterial cell to another and
alter the genetic characteristics.
• For example: In specialized transduction the gal gene, a cell lacking
ability to metabolize galactose could acquire 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.
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27. References..
• An Introduction to Genetic Analysis. 7th edition. Griffiths AJF, Miller
JH, Suzuki DT, et al.New York: W. H. Freeman; 2000
• online Medical Microbiology guide for students
http://microbeonline.com/key-information-regarding-gene-transfer-
mechanism-bacteria.
• Transduction - An Introduction to Genetic Analysis - NCBI
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28. Thank you………
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