Phage

A Phage or Bacteriophage (from the Greek word phagein meaning "to eat") is a class of virus that will infect bacterial hosts. They are also used as model organisms for the study of the molecular biology and replication of viruses. A key example is the T4 phage that will infect an E. coli host cell. T4 phages are made up of a protein head containing the genetic information of the virus, along with a tail and tail fibres that permit the injection of genetic material into the host cell, these structures are made of protein . Bacteriophages are thought to be the most abundant organisms in the world with an estimated 10³¹ in existence. This is a greater number than all other organisms put together, including bacteria .