Caption

Bacteriophages escaping from a dying bacterial cell (Streptococcus sp.), coloured scanning electron micrograph (SEM). This bacteriophage was discovered in freshwater near a sewage outlet. A bacteriophage, also known as a phage, is a virus (virion) that infects a bacterium. It consists of a head (capsid), containing the genetic material (either RNA or DNA) and usually a tail and tail fibres (not seen), which the phage uses to attach to a specific receptor sites on the bacterium. This specific binding means that a bacteriophage can only infect certain bacteria bearing specific receptors. Once attached to the cell surface genetic material is injected into the bacterium, taking over the bacterium's own cellular machinery and forcing it to produce more copies of the bacteriophage. When sufficient numbers have been produced the phages escape from the bacterium by cellular lysis, killing the bacterium in the process. Magnification: x21,335 when shortest.