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Altruism and cannibalism in bacterial colonies

Researchers have found that besides bacteria that commit suicide to save their friends, there are those that kill to survive; Under conditions of distress, bacteria secrete substances that cause their neighbors to die - and the dead release nutrients into the environment

Marit Sloin, Haaretz, Walla News!

Bacteria under a microscope

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One of the survival mechanisms in societies caught in dire conditions is altruism - individuals commit suicide and thus allow other individuals in society to survive. Altruistic behavior is not limited to human society or developed animals, but is also found in poor populations such as bacteria. But the bacteria are not satisfied with that.

In an article published in the electronic edition of the journal "Science", researchers from Harvard University report that they also discovered "cannibalism" among bacteria. Under conditions of distress, bacteria secrete substances that cause their neighbors to die. The dead bacteria release nutrients into the environment, which feed the cannibalistic bacteria, thus improving the survival ability of the entire population.

The phenomenon of cannibalism was discovered in bacteria just before they were forced to switch to another, more stable life form, called a spore (spore), due to a lack of food or extreme temperatures. Similar to seeds in the plant world, the bacteria are covered with a hard and stable wall, which enables survival in extreme conditions. The genetic material of the bacterium is compressed and so is the cell fluid, and around all this a thick wall is formed that isolates it from the external environment. The spore can lie dormant for many years, until conditions improve and allow germination. During germination the outer layer falls off and the bacterium returns to normal life. The creation of the spore is a complicated process that requires huge amounts of energy and takes several hours. If during this time the environmental conditions improve, the cells that have become spores are now at a disadvantage compared to their neighbors. Therefore, bacteria are expected to delay the germination process as much as possible, until the environmental conditions actually endanger their lives.

Under starvation conditions, two subpopulations are formed

The group of researchers from Harvard University, led by Richard Losick, studied Bacillus subtilis bacteria that form spores (spores of another bacterium, Bacillus anthrax, are used in biological warfare). They grew the bacteria under starvation conditions, which forced them to begin the process of creating spores. To the researchers' surprise, it turned out that the bacteria were able to delay the process by killing their neighbors and feeding on the nutrients that were released after their death.

Advertisement The cannibalism, the researchers found, was made possible thanks to two proteins created in the starving bacteria. The first, which the researchers called a "killing factor", is a toxic protein that the bacterium takes care to remove using a "pump" that it activates in the cell wall. In this way, the bacterium avoids poisoning itself, while the cells around it are destroyed. The second protein is an intercellular communication protein that stops the bacteria from turning into spores. The two proteins work together and ultimately cause a double result: on the one hand - the death of the cells that absorb them, and on the other hand - the postponement of the creation of spores in the cells that secrete them.

Under starvation conditions, the researchers believe, two subpopulations with different behavior are formed in the bacterial population. One produces the killing factor and activates the pump that removes it, and also activates the protein that stops the process of turning into a spore; The second subpopulation does not produce both proteins - and is doomed to die.

They know evolution in action

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