In many habitats of bacteria nutrients and other substances which bacteria need for living are quite rare. For this reason the different bacteria strains living there compete and fight each other to ensure the surviving of the own strain. These habitats are like some really bad districts in Chicago in the 1920s and 1930s, where different mafia families fought for the dominance in these districts. Like the mafia in these years, there are also some really bad guys among the bacteria, which do not hesitate to kill their competitors if this brings an advantage to them or to their strain. Therefore some bacteria developed the ability to produce toxins, so called bacteriocins. Some strains of Escherichia coli, the bacteria I introduced to you above, are able to produce different kinds of toxic proteins. These toxic proteins are called colicins, because they are bacterio'''cins''' and they are produced by ''E. '''''coli''''' cells. There are many different ways how colicins act, but the result is always the same: They kill any foreign competitors which do not produce the immunity protein to this specific colicin. This immunity protein is only produced by the bacteria strain also producing the corresponding colicin. It interacts with the colicin protein and ensures by this, that the other bacteria of this strain are not killed if one bacterium starts the colicin production. But this immunity protein can only neutralize the associated colicin. In contrast to the immunity proteins, the colicins are not produced all the time. Their production is regulated by a so called SOS promoter. Therefore the ''E. coli'' will only start the colicin production if it get stressed. This can happen for example if there are not enough nutrients or if there are too many other bacteria around. So better never stress an ‘’E. coli’’! And I am really serious about this, because if you think “what can such a small organisms with its proteins targeted to other bacteria harm me?” you are really on the wrong track. Researches could show that some kinds of colicin proteins are not only able to harm prokaryotic cells like bacteria but also eukaryotic cells like human cells! Thus researches attempt to make use of this dangerous discovery by trying to fight not only dangerous pathogenic prokaryotic cells with colicins but also dangerous body-own eukaryotic cells i.e. cancer cells. But these approaches are only at the beginning, but who knows perhaps we will have a therapy against an infection or against cancer based on colicins one time…
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