The Many Different Families of Phages

Throughout this module we have looked at various methods of how to grow phage’s, different conditions that they like and that sort of thing. But we haven’t talked much about different families and types of phage’s. So I decided to go find out a bit about them

Bacteriophages have been divided into 3 orders, Caudovirales, Ligamenvirales and unassigned.

Caudovirales are known as the tailed viruses and consist of a head and tail. The order contains 3 families. Called Siphoviridae, Myoviridae and Podoviridae. They infect bacteria by using their tails to punch a hole through through the bacterial cell wall and plasma membrane, then injecting their DNA from the head into the cell through the tail.

Siphoviridae- Siphoviridae are characterized by their nonenveloped capsule heads, and their noncontractile tails. The heads are usually have a 60nm diameter. These types of phages have double stranded, linear DNA that is usually around 50 kilobases long.

Myoviridae- Myoviridae are nonenveloped viruses and consist of a head and a tail separated by a neck. The head can be between 50 and 110nm in diameter and has icosahedral symmetry. The tail has helical symmetry and can be between 16 and 20nm in diameter. It is made from a centeral tube, a contractile sheath, and various other small parts. Myoviridae use their tail to inject their DNA into the host cell. Contractions of the tail require ATP so the virus must be attached to a host bacteria for this to occur.

A Myoviridae genome is linear, double stranded DNA that is usually between 33.6 and 170 kilobases long.

Podoviridae- like the other two families, Podoviridae is nonenveloped, has a head that is 60nm in diameter, and a tail. Unlike the other two tailed families however Podoviridae have a very short tail with a maximum length of 17nm.

Their genome is double stranded and linear and is 40-42 kilobases long.

Ligamenvirals are rod like viruses that infect Achaea. There are two families in the order,Lipothrixviridae and Rudiviridae, both of which are composed of a helical protein nucleocapsid with fibres or more complex structures at each end that are used for adhesion to Achaea.

Lipothrixviridae- Lipothrixviridae are enveloped, rod-shaped viruses that infect thermophilic Achaea of the kingdom Crenarchaeota. There is a lot of variation in how long Lipothrixviridae can be, between 410 and 1950nm. And it is 24-38nm in diameter.

Rudiviridae- there are only two known species of rudiviridae both of which infect hyperthermophilic Achaea of the Crenarchaeota kingdom. They are not very well understood, but consist of a tube-like superhelix of DNA surrounded by a protein coat, and three tail fibres (not actual tails) at each end that are thought to be used for adhesion to their hosts. Rudiviridae are stiff rods, that are 830-900nm long and about 23nm in width. Their genomes are made from linear, double stranded DNA and are 32.3 and 35.8 kilobase pairs long.

Unassigned bacteriophages- there are 13 unassigned bacteriophage families, all of which are unique and do not fit into current models. They come in many different shapes, some have circular DNA, and they may or may not be enveloped.

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