The
aim of this practical is to investigate how varying volumes of bacteriophage can
affect the transduction rate using E. coli as the recipient strain. I wanted to
test the hypothesis: ‘The higher the volume of bacteriophage lysate the higher
the number of bacteria colonies on the agar plates.’

The
process of Transduction is where DNA is transferred to a bacterial strain to
another via a virus otherwise known as a Bacteriophage. Transduction can occur
through two different cycles called the Lytic cycle or the lysogenic Cycle.

The
Lytic Cycle is where the bacteriophage replicates inside the host cell and releases
completely new cells that only contains the injected DNA. The bacteriophage
will inject its nucleic acid into the host cell by attaching itself to the
cells surface allowing the DNA to be released inside. The bacteriophage will
then manipulate the host cells’ replication mechanisms to make more viruses.
Following transcription of the injected DNA into messenger RNA, it can control the
host cells ribosomes allowing the destruction of the host cell’s DNA. After the
replication of roughly 200 new bacteriophages the host cell will burst due to
high osmotic pressure inside the cell enabling the newly formed viruses to be
released into the body. The reproduction of viruses will continue at a rapid
rate.  

The
lysogenic cycle is when the DNA in the bacteriophage will combine with the host
cells DNA to produce a Prophage. Bacteriophages infect the host cell and its
DNA will be injected into host cells cytoplasm. An enzyme then breaks down the
hosts cells DNA. The DNA fragment of the host’s original DNA will recombinate
(homologous recombination) with the newly injected DNA and this produces a cell
which contains a mixture of both the original DNA and newly injected DNA. This
is called the Transductant. When the host cell replicates the newly produced
daughter cells will contain both the original cells’ DNA and the bacteriophage
DNA. These daughter cells are called Lysogens. The lysogenic cycle can continue
for an extended period of time but the lysogens can always switch to the lytic
cycle whenever it is required. For the transfer the process of Induction is
needed where the DNA in the prophage is taken and is transcribed and translated
into coating proteins which regulate lytic growth. After the growth period has
concluded the lytic cycle will begin and where the host cell will inevitably be
destroyed. This lysogenic cycle is slower than the lytic cycle and will occur
at a normal prokaryotic reproduction rate. Bacteriophages that utilize the
lysogenic and lytic cycle are named Temperate Phage’s whilst bacteriophages that
only replicate using the lytic cycle are called Virulent Phages.