cyu
3rd November 2012, 23:01
One might think that cooperation by itself should be enough of a kick to give certain groups a survival advantage. It looks like in this case, these bacteria have even evolved a genetic secondary backup to ensure the success of cooperation.
http://www.science20.com/caution_pondering_scientist_ahead/altruistic_gene-95500
We humans take great pride in our ability to come together and cooperate as a society. many microbes cooperate as well. A conundrum among scientists has been how bacteria manage to prevent cheaters from taking over their population, even without jails or stocks or scarlet letters.
Many bacteria cooperate when they reach high population density. secreting extracellular enzymes would be a waste for a lone bacterium. If a lot of bugs all secrete enzymes at once, the digested nutrients will build up to a high enough concentration for all to benefit. bacteria secrete "quorum sensing" (QS) molecules that allow them to detect how many of their fellows are around. When they reach quorum, the bacteria switch on their high-cell-density genes.
Cheaters wouldn't make or release digestive enzymes, but they would still get to eat the nutrients broken down by all the cooperators. Cheaters have an immediate advantage, yet in the wild we mostly see cooperators. Why?
as a control, they grew the bugs on just casein, which requires secreted enzymes to digest. As expected, cheater mutants emerged and took over nearly half the population within a few weeks. But when they added another food source (adenosine) to the medium, the cheaters never prospered!
Adenosine is metabolized inside the cell. But adenosine metabolism is one of those private genetic systems paradoxically controlled by QS. It turns out that by putting adenosine metabolism under QS control, pseudomonas has rigged the game so that when cooperators turn on their QS switch, they get enough private benefit (from adenosine) in addition to public benefit (from casein) that they grow better than cheater mutants with broken QS switches (who get free casein but no adenosine).
The bacteria put genes controlling some private goods under control of the same genetic switch that controls public goods, which ensures that cooperators are those who prosper.
http://www.science20.com/caution_pondering_scientist_ahead/altruistic_gene-95500
We humans take great pride in our ability to come together and cooperate as a society. many microbes cooperate as well. A conundrum among scientists has been how bacteria manage to prevent cheaters from taking over their population, even without jails or stocks or scarlet letters.
Many bacteria cooperate when they reach high population density. secreting extracellular enzymes would be a waste for a lone bacterium. If a lot of bugs all secrete enzymes at once, the digested nutrients will build up to a high enough concentration for all to benefit. bacteria secrete "quorum sensing" (QS) molecules that allow them to detect how many of their fellows are around. When they reach quorum, the bacteria switch on their high-cell-density genes.
Cheaters wouldn't make or release digestive enzymes, but they would still get to eat the nutrients broken down by all the cooperators. Cheaters have an immediate advantage, yet in the wild we mostly see cooperators. Why?
as a control, they grew the bugs on just casein, which requires secreted enzymes to digest. As expected, cheater mutants emerged and took over nearly half the population within a few weeks. But when they added another food source (adenosine) to the medium, the cheaters never prospered!
Adenosine is metabolized inside the cell. But adenosine metabolism is one of those private genetic systems paradoxically controlled by QS. It turns out that by putting adenosine metabolism under QS control, pseudomonas has rigged the game so that when cooperators turn on their QS switch, they get enough private benefit (from adenosine) in addition to public benefit (from casein) that they grow better than cheater mutants with broken QS switches (who get free casein but no adenosine).
The bacteria put genes controlling some private goods under control of the same genetic switch that controls public goods, which ensures that cooperators are those who prosper.