Lecture 2 - Transduction | Genetics (Zoology) by ILLL, DU - Biotechnology Engineering (BT) PDF Download

 Page 1


 Transduction  
 
1 
 
 
 
 
 
 
 
 
 
 
 
Lesson: Transduction 
Lesson Developer : Dr. Shailly Anand  and Dr. Jasvinder Kaur 
College/ Department : Molecular Biology Laboratory, Department of 
Zoology,University of Delhi 
 
 
 
  
Page 2


 Transduction  
 
1 
 
 
 
 
 
 
 
 
 
 
 
Lesson: Transduction 
Lesson Developer : Dr. Shailly Anand  and Dr. Jasvinder Kaur 
College/ Department : Molecular Biology Laboratory, Department of 
Zoology,University of Delhi 
 
 
 
  
 Transduction  
 
2 
 
 
Table of Contents 
Unit: Recombination in Bacteria 
Chapter 3: Transduction 
? Introduction 
 
? Historical background 
? Discovery: Joshua Lederberg and Norton Zinder (1951) 
? Physical transfer of DNA during transduction: K. Ikeda and J. 
Tomizawa (1965)  
 
? The Process of Transduction   
? Lytic vs Lysogenic cycle 
? Events in the process of transduction 
(Adsorption, Penetration, Replication, Transcription & 
translation, Assembly and Release) 
  
? Types of Transduction 
? Generalized transduction 
? Complete 
? Abortive 
? Specialized transduction 
 
? Importance of Transduction 
? Summary 
? Glossary 
? Practice Questions 
Page 3


 Transduction  
 
1 
 
 
 
 
 
 
 
 
 
 
 
Lesson: Transduction 
Lesson Developer : Dr. Shailly Anand  and Dr. Jasvinder Kaur 
College/ Department : Molecular Biology Laboratory, Department of 
Zoology,University of Delhi 
 
 
 
  
 Transduction  
 
2 
 
 
Table of Contents 
Unit: Recombination in Bacteria 
Chapter 3: Transduction 
? Introduction 
 
? Historical background 
? Discovery: Joshua Lederberg and Norton Zinder (1951) 
? Physical transfer of DNA during transduction: K. Ikeda and J. 
Tomizawa (1965)  
 
? The Process of Transduction   
? Lytic vs Lysogenic cycle 
? Events in the process of transduction 
(Adsorption, Penetration, Replication, Transcription & 
translation, Assembly and Release) 
  
? Types of Transduction 
? Generalized transduction 
? Complete 
? Abortive 
? Specialized transduction 
 
? Importance of Transduction 
? Summary 
? Glossary 
? Practice Questions 
 Transduction  
 
3 
 
? Answer to the Questions 
? References 
Introduction 
Genetic engineering in bacteria involves three primary methods. Firstly, conjugation during 
which genetic material is transferred from one cell to another by direct cell to cell contact. 
Secondly, transformation in which the DNA present in the medium gets into the cell by 
subjecting it to different treatments like heat shock or electroporation. The third method 
involves the use of a bacteriophage (bacteria infecting virus) to transfer the genetic material 
from the donor to the recipient cell. Each of these methods of recombination in bacteria 
results in change in the genetic composition of the cell and hence brings about variations. 
These methods have been used widely in biotechnological processes to transfer the gene of 
interest into the host cell for production of proteins of use. This chapter focuses on the 
method of DNA transfer mediated by bacteriophage i.e. transduction, its historical 
background, the steps in the process, its types and its significance.  
 
Historical Background 
Discovery: Joshua Lederberg and Norton Zinder (1951) 
They worked on two auxotroph strains of Salmonella typhimurium denoted by Strain A and 
Strain B. Their first experiment was similar to the one in which they demonstrated the 
process of conjugation. Strain A could not synthesize phenylalanine (phe), tryptophan (trp) 
and tyrosine (tyr) while Strain B could not synthesize methionine (met) and histidine (his). 
Therefore, when grown in minimal medium, these components had to be added to the 
medium respectively. Strain A could thus be designated as phe
- 
trp
- 
tyr
- 
while Strain B was 
denoted by met
- 
his
-
. Three experimental set ups were then prepared as under: 
Experiment 1: (Control) Culture of Strain A was plated on minimal medium. 
Experiment 2: (Control) Culture of Strain B was plated on minimal medium. 
Experiment 3: Culture of Strain A and B was mixed together and incubated at optimum 
condition. It was then plated on minimal medium. 
Page 4


 Transduction  
 
1 
 
 
 
 
 
 
 
 
 
 
 
Lesson: Transduction 
Lesson Developer : Dr. Shailly Anand  and Dr. Jasvinder Kaur 
College/ Department : Molecular Biology Laboratory, Department of 
Zoology,University of Delhi 
 
 
 
  
 Transduction  
 
2 
 
 
Table of Contents 
Unit: Recombination in Bacteria 
Chapter 3: Transduction 
? Introduction 
 
? Historical background 
? Discovery: Joshua Lederberg and Norton Zinder (1951) 
? Physical transfer of DNA during transduction: K. Ikeda and J. 
Tomizawa (1965)  
 
? The Process of Transduction   
? Lytic vs Lysogenic cycle 
? Events in the process of transduction 
(Adsorption, Penetration, Replication, Transcription & 
translation, Assembly and Release) 
  
? Types of Transduction 
? Generalized transduction 
? Complete 
? Abortive 
? Specialized transduction 
 
? Importance of Transduction 
? Summary 
? Glossary 
? Practice Questions 
 Transduction  
 
3 
 
? Answer to the Questions 
? References 
Introduction 
Genetic engineering in bacteria involves three primary methods. Firstly, conjugation during 
which genetic material is transferred from one cell to another by direct cell to cell contact. 
Secondly, transformation in which the DNA present in the medium gets into the cell by 
subjecting it to different treatments like heat shock or electroporation. The third method 
involves the use of a bacteriophage (bacteria infecting virus) to transfer the genetic material 
from the donor to the recipient cell. Each of these methods of recombination in bacteria 
results in change in the genetic composition of the cell and hence brings about variations. 
These methods have been used widely in biotechnological processes to transfer the gene of 
interest into the host cell for production of proteins of use. This chapter focuses on the 
method of DNA transfer mediated by bacteriophage i.e. transduction, its historical 
background, the steps in the process, its types and its significance.  
 
Historical Background 
Discovery: Joshua Lederberg and Norton Zinder (1951) 
They worked on two auxotroph strains of Salmonella typhimurium denoted by Strain A and 
Strain B. Their first experiment was similar to the one in which they demonstrated the 
process of conjugation. Strain A could not synthesize phenylalanine (phe), tryptophan (trp) 
and tyrosine (tyr) while Strain B could not synthesize methionine (met) and histidine (his). 
Therefore, when grown in minimal medium, these components had to be added to the 
medium respectively. Strain A could thus be designated as phe
- 
trp
- 
tyr
- 
while Strain B was 
denoted by met
- 
his
-
. Three experimental set ups were then prepared as under: 
Experiment 1: (Control) Culture of Strain A was plated on minimal medium. 
Experiment 2: (Control) Culture of Strain B was plated on minimal medium. 
Experiment 3: Culture of Strain A and B was mixed together and incubated at optimum 
condition. It was then plated on minimal medium. 
 Transduction  
 
4 
 
Upon incubation it was observed that in case of experiment 1 and 2, no growth was seen on 
the plates while in case of experiment 3, a few colonies appeared. These prototrophs could 
thus synthesize all the components required for the growth and survival and represented 
met
+ 
his
+ 
phe
+ 
trp
+ 
tyr
+
.  
By that time, Bernard Davis had proposed the requirement of direct cell contact for 
conjugation by his famous U- tube experiment. Using the Davis tube, Lederberg and Zinder 
proceeded with their next experiment using the above strains. They separated the two sides 
of the U-tube using a filter but with varied pore size. Fortuitously, they obtained some 
recombinants in the filter that could survive on the minimal medium without any 
supplements (i.e. prototrophs). They then concluded that in absence of any physical contact 
between the cells, recombination or transfer of DNA can be mediated by an agent that could 
pass through the filter pores. Based on the pore size, size of this agent matched with that of 
a virus, P22 (a temperate phage of Salmonella).  
The above experiment provided the first evidence for a new method of transfer i.e. a 
bacteriophage (or phage in short) carrying the DNA from one cell to another.  This was later 
named as transduction. It also involved the presence of a donor and a recipient cell. 
 
Physical transfer of DNA during transduction: K. Ikeda and J. 
Tomizawa (1965) 
They used the method of density labeling of DNA in P1 phage (Fig. 1). In their experiment 
they cultured the donor bacteria in a medium containing the heavy isotope of nitrogen and 
hydrogen (
15
N and 
2
H). This resulted in the synthesis of a dense DNA (by replication). The 
cells were then shifted to the normal medium (i.e. containing 
14
N and 
1
H) and infected with 
phage P1. The phage thus was able to synthesize the normal light DNA. Upon packaging of 
the newly synthesized DNA into the capsids (virus heads or protein coat), it was observed 
that the phage DNA was heavier than expected. This indicated that during packaging, it 
incorporated the bacterial DNA as well. When this phage was allowed to infect the recipient 
bacteria, it transferred the heavy DNA to the recipient. This experiment clearly 
demonstrated that transduction involved two important aspects i.e. the packaging of the 
donor bacterial DNA into the newly synthesized phages and secondly, transfer of this DNA to 
the recipient cell (Fig. 1). Similar results were obtained by Ebel-Tsipis et al. (1972) who 
worked on P22 phages. 
Page 5


 Transduction  
 
1 
 
 
 
 
 
 
 
 
 
 
 
Lesson: Transduction 
Lesson Developer : Dr. Shailly Anand  and Dr. Jasvinder Kaur 
College/ Department : Molecular Biology Laboratory, Department of 
Zoology,University of Delhi 
 
 
 
  
 Transduction  
 
2 
 
 
Table of Contents 
Unit: Recombination in Bacteria 
Chapter 3: Transduction 
? Introduction 
 
? Historical background 
? Discovery: Joshua Lederberg and Norton Zinder (1951) 
? Physical transfer of DNA during transduction: K. Ikeda and J. 
Tomizawa (1965)  
 
? The Process of Transduction   
? Lytic vs Lysogenic cycle 
? Events in the process of transduction 
(Adsorption, Penetration, Replication, Transcription & 
translation, Assembly and Release) 
  
? Types of Transduction 
? Generalized transduction 
? Complete 
? Abortive 
? Specialized transduction 
 
? Importance of Transduction 
? Summary 
? Glossary 
? Practice Questions 
 Transduction  
 
3 
 
? Answer to the Questions 
? References 
Introduction 
Genetic engineering in bacteria involves three primary methods. Firstly, conjugation during 
which genetic material is transferred from one cell to another by direct cell to cell contact. 
Secondly, transformation in which the DNA present in the medium gets into the cell by 
subjecting it to different treatments like heat shock or electroporation. The third method 
involves the use of a bacteriophage (bacteria infecting virus) to transfer the genetic material 
from the donor to the recipient cell. Each of these methods of recombination in bacteria 
results in change in the genetic composition of the cell and hence brings about variations. 
These methods have been used widely in biotechnological processes to transfer the gene of 
interest into the host cell for production of proteins of use. This chapter focuses on the 
method of DNA transfer mediated by bacteriophage i.e. transduction, its historical 
background, the steps in the process, its types and its significance.  
 
Historical Background 
Discovery: Joshua Lederberg and Norton Zinder (1951) 
They worked on two auxotroph strains of Salmonella typhimurium denoted by Strain A and 
Strain B. Their first experiment was similar to the one in which they demonstrated the 
process of conjugation. Strain A could not synthesize phenylalanine (phe), tryptophan (trp) 
and tyrosine (tyr) while Strain B could not synthesize methionine (met) and histidine (his). 
Therefore, when grown in minimal medium, these components had to be added to the 
medium respectively. Strain A could thus be designated as phe
- 
trp
- 
tyr
- 
while Strain B was 
denoted by met
- 
his
-
. Three experimental set ups were then prepared as under: 
Experiment 1: (Control) Culture of Strain A was plated on minimal medium. 
Experiment 2: (Control) Culture of Strain B was plated on minimal medium. 
Experiment 3: Culture of Strain A and B was mixed together and incubated at optimum 
condition. It was then plated on minimal medium. 
 Transduction  
 
4 
 
Upon incubation it was observed that in case of experiment 1 and 2, no growth was seen on 
the plates while in case of experiment 3, a few colonies appeared. These prototrophs could 
thus synthesize all the components required for the growth and survival and represented 
met
+ 
his
+ 
phe
+ 
trp
+ 
tyr
+
.  
By that time, Bernard Davis had proposed the requirement of direct cell contact for 
conjugation by his famous U- tube experiment. Using the Davis tube, Lederberg and Zinder 
proceeded with their next experiment using the above strains. They separated the two sides 
of the U-tube using a filter but with varied pore size. Fortuitously, they obtained some 
recombinants in the filter that could survive on the minimal medium without any 
supplements (i.e. prototrophs). They then concluded that in absence of any physical contact 
between the cells, recombination or transfer of DNA can be mediated by an agent that could 
pass through the filter pores. Based on the pore size, size of this agent matched with that of 
a virus, P22 (a temperate phage of Salmonella).  
The above experiment provided the first evidence for a new method of transfer i.e. a 
bacteriophage (or phage in short) carrying the DNA from one cell to another.  This was later 
named as transduction. It also involved the presence of a donor and a recipient cell. 
 
Physical transfer of DNA during transduction: K. Ikeda and J. 
Tomizawa (1965) 
They used the method of density labeling of DNA in P1 phage (Fig. 1). In their experiment 
they cultured the donor bacteria in a medium containing the heavy isotope of nitrogen and 
hydrogen (
15
N and 
2
H). This resulted in the synthesis of a dense DNA (by replication). The 
cells were then shifted to the normal medium (i.e. containing 
14
N and 
1
H) and infected with 
phage P1. The phage thus was able to synthesize the normal light DNA. Upon packaging of 
the newly synthesized DNA into the capsids (virus heads or protein coat), it was observed 
that the phage DNA was heavier than expected. This indicated that during packaging, it 
incorporated the bacterial DNA as well. When this phage was allowed to infect the recipient 
bacteria, it transferred the heavy DNA to the recipient. This experiment clearly 
demonstrated that transduction involved two important aspects i.e. the packaging of the 
donor bacterial DNA into the newly synthesized phages and secondly, transfer of this DNA to 
the recipient cell (Fig. 1). Similar results were obtained by Ebel-Tsipis et al. (1972) who 
worked on P22 phages. 
 Transduction  
 
5 
 
 
Figure 1: Ikeda and Tomizawa’s experiment (1965) – Bacteria grown in medium with heavy 
isotopes of nitrogen and hydrogen was infected with phage. The lytic cycle of phage 
resulted in some progenies carrying the heavy bacterial DNA. This phage when allowed to 
infect bacteria grown in normal medium got integrated in its chromosome. Subsequent 
isolation, fragmentation and separation of DNA showed both heavy and light DNA profiles 
thereby indicating the transfer of DNA from the donor cell to the recipient cell. 
Source: Author