Why Do Even Microbes Commit Suicide?

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E. coli cells
Rocky Mountain Laboratories, NIAID, NIH

A study on suicidal E. coli sheds light on why organisms throughout the animal kingdom, big and small, sometimes decide to do themselves in.

The good news is that suicide appears to be comparatively rare in larger animals, but more common among microscopic life forms, such as microbes, according to the study, published in the latest Proceedings of the Royal Society B.

Natural selection -- the process by which organisms that adapt to their environment tend to survive and produce more offspring -- favors suicide when the death guarantees the survival of relatives and the individual is less likely to reproduce in future.

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An example of this, according to study co-author Rolf Kümmerli, is when "a parent saves his children out of a burning house. This is beneficial because the rescued relatives share many of the genes with the suicidal helper." Many people are driven to save their kids and close loved ones, no matter what.

Other forms of suicide among humans, such as bombers on a kamikaze mission, likely have nothing to do with natural selection, and instead reflect the by-product of something else. In the case of the bomber, that could be the individual's environment and life’s experiences. Depression or other forms of mental illness, however, could be inherited.

Kümmerli, a professor in the department of Microbial Evolutionary Ecology at the University of Zürich, and colleagues Dominik Refardt and Tobias Bergmiller investigated the suicidal behavior of E. coli. Some cells of this common bacteria will kill themselves in the presence of bacteria-killing parasitic viruses.

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Kümmerli explained to Discovery News that when a protein of an E. coli cell senses viral attack, it becomes activated and, with other proteins, triggers drainage of membrane holes of the bacterial cell. It’s as though the cell biochemically stabs itself.

"Consequently, vital cell liquid and components pour out into the environment, which leads to cell death," he said. "The dead cell is presumably like an empty perforated sack."

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