Like any other living organism, bacteria can be attacked by certain viruses and thus become ill. Such viruses are called bacteriophages (phages for short), which means "bacteria eaters". Bacteriophages can be found wherever bacteria are found. A phage has a very simple structure: It essentially consists of a shell that protects the genetic material it contains. This envelope can have various forms and attachments. The viral infection of a bacterium always follows the same pattern: first, the phage docks onto special structures on the outer shell of the bacteria. In the next step, the phage injects its genetic material directly into the host cell. There, the phage genetic material is either incorporated into the host's genes and put into a kind of dormant state - or new phages are immediately produced. The phage forces the host to gradually produce all the phage components and assemble them into new phages. Finally, the bacterium bursts and releases the new phages.

This ability to specifically destroy bacteria is utilised by humans in phage therapy: Bacteriophages are used specifically to kill disease-causing bacteria. However, phages can also cause great economic damage if, for example, they infect bacteria that are needed for cheese production.

© Text and figure Katrin Weidenbach / VAAM, kweidenbach[at]ifam.uni-kiel.de, Use according to CC 4.0