Bacteria playing rock-paper-scissors grow to be merciful

Important news from the University of Washington: allowing bacteria to play rock paper scissors teaches them the value of restraint.


Image CC Mike Souza

Researchers created a group of E. coli bacteria locked in a non-transitive game of survival. Non-transitive refers to situations where each player is weak against another in the field, such as rock-paper-scissors. One type of bacteria produced two antibiotics, the remaining bacteria were either resistant to the antibiotics, or sensitive to them. All three types were dropped into 192 wells, between which they could migrate.

On occasion, a super-competitor (nicknamed Rock*, very droll) evolved in the antibiotic-resistant community, allowing it to push out the antibiotic-producing type and expand rapidly across the wells. However, this tactic would eventually put Rock* in direct competition with the third, antibiotic-sensitive bacteria. As this one outcompeted Rock* in the absence of antibiotics, the aggressive strategy would unltimately end in Rock*'s demise.

Thus the bacteria were encouraged to co-exist peacefully by employing restraint against their enemies. However, the system only worked when migration was restricted - if the bacteria were free to move around, a pacifist nature was no defence against other bacteria. Of course, we shouldn't be surprised that engineering a non-transitive game, even one played out by living cells, acts according to the rules. But it's an interesting analogy to real life ecology, such as the tri-fold mating systems of larger organisms like lizards.

The research is published in the Proceedings of the National Academy of Sciences. via


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