It’s not surprising that colonies of bacteria use chemical attacks to prevent rival colonies from encroaching on their territory. What is surprising is that these attacks occur even between colonies of the same species, and even between colonies that were started from the same parent cell.
Avraham Be’er and Harry Swinney of the University of Texas and Eshel Ben-Jacob of UC San Diego and Tel Aviv University have been studying just how this intrafamily warfare is conducted. The scientists inoculated Petri plates with the bacteria Paenibacillus dendritiformis. Normally, this bacterium grows in colonies that spread out in fine branches in every direction. However, when two seemingly identical colonies were placed on the same plate, they left a conspicuous void between them.
Poisons are unleashed when colonies of bacteria get too close and create a toxic "no-man's land" in between.
Credit: Eshel Ben-Jacob
Upon further study, the researchers found that the empty space was created not but any lack of nutrients, but by the addition of a protein subsequently named ‘sibling lethal factor’. This protein actually starts as a gene product that is two-thirds larger and harmless. After being trimmed down to size by the protease ‘subtilisin’, the newly discovered factor kills any bacterium that wanders too close.
Just why these sibling colonies would lash out at each other rather than simply blending into one super-colony is not clear. As explained by Ben-Jacob:
It supports the notion that each colony is a superorganism, a multicellular organism with its own identity.