MICROBIOLOGY

1. PRESENTED BY:
MOUSAMI JARIA
ST. GEORGE COLLEGE OF
MANAGEMENT AND SCIENCE
MSC MICROBIOLOGY
SEMESTER-2

2.  Transduction is a method of gene transfer in
bacteria from donor to recipient using
bacteriophage.
 In transduction at first bacteriophage infects donor
bacteria and then carries some part of donor
genome with it.
 When this bacteriophage infects new bacterial cell
, it transfer that DNA in to recipient cell.
 There are two types of transduction:
1. Generalized transduction
2. Specialized transduction.

4.  It was discovered by Joshua Lederberg and
Norton Zinder in 1952.
 They were testing for recombination in the
bacterium Salmonella typhimurium .
 The researchers grew two different strains of the
bacterium (one was met- his- & other was phe-
trp- tyr-) on a medium with less nutritional
components and when observed , no wild type
was found.
 However they found that when two bacteria were
combined wild type cells appeared.

5.  The researchers also found some ‘’recombiants’’
(organisms with one or more segments or genes
have been inserted into their DNA) in the culture.
 By preventing cell contact with filters of varying
size , the researchers found the one responsible
for the rise of recombiant – a temperate
bacteriophage of Salmonella.
 Hence the researchers discovered a new process
of gene transfer in organisms, mediated by virus .

7.  Bacteriophages are natural vectors that
transduce DNA from one bacterial cell to another
 A bacteriophage cannot ‘’ live ‘’ or reproduce
without getting inside a bacterial cell

8. There are two types of transduction :
1. Generalized Transduction
2. Specialized transduction
 GENERALIZED TRANSDUCTION (Lytic Cycle):
 This is a method of transduction that allow genes
to be transferred from one bacterium to the other .
 This happens when a virus accidentally transfers
its genetic material , the same way it infects plant
and animal cells & other bacterial cells.

9.  Virus (or bacterial phages in this case) cannot replicate
their own DNA, thus they infect a host cell and take over
the machinery to replicate their own . When it is done ,
parts of the virus are aggregated and released to infect
other cells.
 To complete the process , parts of the host chromosomes
must be destroyed and needs to be reassembled for the
viral DNA to be inserted.
 Due to random chances of infection , the viral DNA is not
inserted but the DNA of its previous host bacterial cell .
And if any recombination happens in the cell with the
new set of genes that is called as generalized
transduction.

10.  This type of transduction occurs during the lytic
cycle of virus where it invades and incorporates its
own DNA to the hosts.
 Eventually this virus will kill its host by bursting the
cell . New viral cells are then ready to infect other
cells.

12.  This transduction involves the specific insertion
of the viral DNA to the host cell.
 Specialized transduction occurs in the life cycle
of the virus and involves an additional phase . It
occurs during the lysogenic sequence of viral
infection.
 As a result a specific spot on the host’s
chromosome gets inserted with bacterial
chromosome.
 In order to complete the cycle , the virus then re-
undergoes the lytic cycle to transfer the genes to
new cell.

13.  The viral DNA do not immediately kills the host
cell.
 Instead , it goes dormant as it inserts its own
DNA to the host and allows it to grow while the
viral DNA gets replicated .
 Soon the virus will reactivate its machinery and
eventually kill the host.

15.  MAPPING OF BACTERIAL GENES:
• The amount of DNA packaged inside the head of
the virus is largely dependent on the size of the
head itself. The cutting of the host chromosome
is done randomly ,with all genes having the
same probability of being packaged and
transmitted to the vector
• The closer the genes are to each other , the
higher chance of them being packaged in the
same fragment of DNA.
• Thus , bacterial genes can be mapped by
calculating their frequencies of being transduced

16.  CONTRIBUTES TO THE INCREASE OF GENETIC
EVOLUTION:
• The process of bacterial transduction generally
increases genetic diversity, as it allows
organisms to adapt to any change in their
environment.
 SERVES AS KEY TO ANTIBIOTIC RESISTANCE:
• Transduction can explain the mechanism by
which antibiotics become ineffective because of
the transfer of genes among bacteria.