Bacteriophage virions. Coloured transmission electron micrograph (TEM) of bacteriophage virions (yellow). A bacteriophage, or phage, is a virus that infects bacteria. It consists of a head, containing the genetic material, a tail and tail fibres (not seen), which fix it to a specific receptor site. The tail injects its genetic material into the bacterium and this hijacks the bacterium's own cellular machinery, forcing it to produce more copies of the bacteriophage. When a sufficient number have been produced, the phages exit the bacterium by lysis, killing it in the process. Magnification: x67,000 when printed 10 centimetres wide.