Transduction: The virus mediated gene transfer in bacteria
The
major threat to the survival of omnipresent bacteria is the much simpler
viruses. Viruses are strict parasites with extremely simple organisation just
the genetic material either DNA or RNA surrounded by a protein coat. Viruses that attack bacteria are called as
bacteriophages. Bacteriophages are the group of viruses involved in
transfer of genetic material from one bacterium to the other. Such virus mediated gene transfer is termed
as transduction. The carrier phage is the transducer or vector.
Transduction was first described by Joshua
Lederberg and Norton Zinder in 1952. Bacteriophages are widely used as
vectors in recombinant DNA technology.
Generalised vs Specialised
Transduction
Different
types of transduction: generalised (random) and specialized (specific DNA fragments).
To
understand transduction in detail, we need to understand the lytic and
lysogenic cycle of bacteriophage replication.
Generalised transduction
Generalised transduction is
mediated by lytic phages where any DNA segment can be transferred
by the virus and may not integrate the segment to the bacterial chromosome.
Here a portion of the donor bacterial DNA accidently gets enclosed in a capsid.
Upon lysis and further infection of this virus particle to another bacterium,
the genetic material of the donor is released and recombination occurs between the
injected DNA segments and homologous part of the recipient chromosome, forming
a rDNA.
Generalised transduction can
be either complete or abortive.
 |
| Generalised transduction |
Complete Transduction vs
Abortive Transduction
In complete transduction,
the exogeneote or the transduced DNA fragment gets integrated within the
recipient bacterial chromosome (endogenote), forming a recombinant chromosome.
This DNA fragment, replicate along with recipient bacterial chromosome replication
and passed on to the daughter cells.
In abortive transduction:
the exogenote may not get integrated with the endogenote and remains in the
cytoplasm as free particle. These fragments cannot undergo replication.
Specialised transduction
Specialised transduction
is mediated by lysogenic phages. Here specific DNA fragment are integrated into
the host chromosome. Here phage DNA gets integrated with the bacterial
chromosome, viral genome integrated into the bacterial genome is called prophage. The prophage undergoes
replication along with bacterial genome replication. Upon induction, the
propahge detaches from the bacterial chromosome. At times, a portion of the
bacterial DNA remains attached to the detached phage DNA. This excised phage
DNA undergoes lytic cycle and infects another bacterium and transfers the
bacterial genes from the donor bacterium. Here
only the bacterial genes that are close to the site of prophage are
transferred. So this transduction is called specialised.
 |
| Specialised transduction |
Lysogenic
phages like lambda phages are widely used as vectors in rDNA technology.
Learn more:
Tags:
Abortive Transduction
Bacterial Recombination
Bacterial transformation
Complete Transduction
conjugation
Generalised Transduction
prophage
Specialised Transduction
transduction