In the struggle between different clones of bacteria up to 95 percent of the cells in the colony can commit suicide to destroy their own membrane. Before that, they accumulate a protein toxic to rivals, and its allocation protects the rest of the colony. The largest mass suicides happening at the front of the battle, where the bacteria would have died anyway from the poison that vydelyayut their competitors. A Preprint of the article posted on the service bioRxiv.
Normally, natural selection eliminates the tendency to actions which lead to the death of the actor. However, in nature there are species that exhibit suicidal behaviour: for example, social insects (termites or ants) or bacteria. Latest destroy the membranes of the cells to produce toxins lethal for opponents. The evolutionary benefit of such actions is understandable, if only a small part of the colony exposes himself to lysis, to protect others. However, to determine which cells kill themselves, and some have died from the actions of opponents, not so easy.
Toxic substances that bacteria secrete in the process of lysis, are called bacteriocins and are specific for different strains. Escherichia coli produces a wide range of proteins kolicinu, they are expressed with small plasmids (pieces of DNA that are found in the cytoplasm of cells). Production kolicinu launches protective of the SOS system of the bacterium in response to DNA damage. The release of toxins can provoke artificially, if you act on a colony of agents that damage DNA. But natural kolicini kill the bacterial cells through the faulty DNA than launch a retaliatory products kolicinu. Such a confrontation reminiscent of the real fighting between the colonies of bacteria.
Eliza Garnet (Granato Elisa) and Kevin foster (Kevin Foster) of Oxford University have found a way to distinguish bacteria suicide by victims of enemy action. It turned out that the well-known dye of propecia iodide, which fluoresces when bound with DNA, only penetrates into cells membrane isiruosiau their own. Thus, the intensity of the illumination it is possible to estimate the number of suicides. In addition to the iodide of propecia, the researchers introduced into the cells of bacteria of plasmids that encode green fluorescent protein. The expression of this dye runs at the same time (same promoter), when the production kolicina E2.
The researchers evaluated the dynamics of excretion kolicina E2 and lysis of nearly eight thousand cells of one strain of bacteria in response to colicin E8, which produces a competitive strain. Then scientists have created the battleground for the two competing clones of bacteria, to see how cells react to nonuniform exposure to the toxins in time and space in the real world. One side was represented by bacteria that produce colicin E2 (as control used by bacteria that do not produce toxins), and the other those whose only weapon is colicin E8.
To test whether the bacteria can lizirovania if their Arsenal is not weapons, the researchers used a genetically modified strain in which the plasmid was not kolicina E2. The colony landed on the substrate, where the concentration kolicina E8 was gradual, as the battlefield of the two clones.
In cells that have literally their membranes, for about 50 minutes before the destruction gradually increased the green fluorescent protein, which corresponded to the accumulation kolicina E2 in the cytoplasm. Then the membrane began to disintegrate, causing a sharp increase in the level associated with DNA of iodide of propedia, and green dye leak out of the cells.