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Hello, everybody.
My name is Colin Hill
and I work at APC
Microbiome Ireland,
based here in University
College Cork in Ireland.
Today, I'm going to
be talking about
bacteriophages as
tools in medicine.
0:15
Bacteriophage (phage) are
viruses that infect bacteria.
They're the most abundant
biological entities on earth.
It's been estimated that
there may be as many
as 10^31 bacteriophages
on Earth.
Far more than there are
bacterial targets for them.
Phage come in all kinds
of shapes and sizes,
and you can see here some
electron micrographs
of phages of different
shapes and sizes.
This is the tip
of the iceberg of
the different
morphologies or shapes
that viruses can
take up a nature.
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I want to say something about
bacteriophage structure.
Most bacteriophages
consist of a protein head,
or a capsid, and a tail.
Trapped within the head
of the bacteriophage is
the genomic information,
or the genes encoded by
that bacteriophage.
Most bacteriophage are
simply the genes they
carry, are just a
blueprint for making
more copies of the phage itself.
Now, the genomic
information can be
encoded by single-stranded RNA,
double-stranded RNA,
single-stranded DNA
or double-stranded DNA.
There is incredible variety
within these bacteriophages
as to the type of genomic
information they carry,
and also the amount of genomic
information they carry.
For example, genomes of
a Microviridae phage
can be very short, only 3-4 kb,
just enough to encode
two or three genes.
Whereas, the biggest phage,
the jumbo phage and mega phage,
they can have genomes of
a million base pairs,
bigger even than the
smallest bacterial genomes,
so tremendous variability again.
The shapes can also
vary a little bit.
The one on top that you
see here is a Podovirus
with a very small tail relative
to the size of the head.
Whereas, on the bottom
is Siphoviridae,
which has a much smaller
head in comparison
to the length of its tail.
The Nobel Prize winner
and immunologist,
Sir Peter Medawar, once
very aptly described
bacteriophages and
viruses in general as,
"a piece of bad news
wrapped in protein".
