Bacteriophages as tools in medicine

Published on September 29, 2022   41 min

A selection of talks on Infectious Diseases

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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.
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.
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".