bacteria tau professor 248.88.
(photo credit: Eshel Ben Jacob)
Politicians and others have much to learn from lowly bacteria when they make life-and-death decisions under stress, according to Tel Aviv University physicist Prof. Eshel Ben Jacob and several theoretical biophysicists at the University of California at San Diego, whose research article on "Sporulation and competence in Bacillus subtilis" was published Monday night in the Proceedings of the National Academy of Sciences.
Ben Jacob and colleagues noted that life is complicated and pressing even for these microscopic creatures, which live in large colonies - each 100 times bigger than the number of humans on Earth. The researchers wondered how they coped, and whether their coping strategies could be described on the molecular level.
Their new study shows how, under conditions of stress, the bacteria communicate with each other using chemical signals and reach decisions in sophisticated ways, using a complex network of genes and proteins to calculate complex possibilities as in "game theory."
Many bacteria, explained Ben Jacob, react to hunger, toxins and DNA damage by creating spores - more resilient versions of themselves that are dormant until conditions are better so they can revive themselves.
More than 500 different genes are involved, and the process can take about 10 hours. It ends when the mother cell dies and the original DNA disintegrates, while its copied genome becomes a spore.
This, unfortunately, cannot occur in higher forms of life, in which the choice is between life or death, said the TAU physicist.
A small number of these bacteria can revert to an intermediate state called "competence" in which the DNA - covered by an "envelope" - can still absorb substances from its environment but the organism is not yet a spore. In this case, they can absorb the DNA of spores that spread through the environment and look for segments resistant to antibiotics (if the stress is caused by these anti-bacterial drugs) or consume them as food (if the stress is due to hunger).
This intermediate state causes a few "chosen" bacteria to survive, even if the environment has not returned to normal, and even reproduce when the situation improves and they no longer need to be spores. The shortcoming is that the alternative is irreversible death if conditions do not improve, with the loss of the DNA.
The research found that only about 10 percent of the bacteria choose the latter state. Here is where game theory - or specifically what is known as the "prisoner's dilemma" - comes in, explained Ben Jacob.
This classic version is about two prisoners. If only one admits he committed a crime, he will get two years in jail, while the other one will get six. If both confess, each will get four years, while if neither does, both will go free. The temptation is not to confess, but one can't be sure if the other will, causing the non-confessor to spend more time behind bars.
But in the bacteria situation, there are not two but trillions of participants, and they have a very limited amount of time to decide, said Ben Jacob.
"Every bacterium has to decide whether it will cooperate [with all turning into spores] or not, in which they will go into the competency state. And unlike the situation of prisoners, an internal clock or timer ticks away. Each bacterium sends out chemical messages about its intentions.
Ben Jacob said that bacteria "usually don't lie" about their own plans, but the minority that do have a chance of being a survivor. Bacteria that "don't want to cheat will postpone their decision, seeing how other bacterial decisions go."
The new article presents a model that decodes how bacteria use the gene-and-protein networks to calculate risks and the game theory principles they use, he concluded.
A similar story involves the decision by Israelis whether to get vaccinated against H1N1 flu or not due to rumors that the shots may have potentially dangerous side effects, suggested Ben Jacob. If everybody else is vaccinated, perhaps it's better not to get the shot because the virus will be wiped out before it reaches us?
The amount of stress in this case is determined by how many people around us get this strain of influenza. The more there are, the more likely one would get the shot. For the same reason, more people could get vaccinated, so then again it wouldn't be worthwhile for us to be vaccinated.
"If we were bacteria, we would compare the numbers who come down with the flu and the rate of vaccination" and learn from them, said Ben Jacob. "The simple rule we learned is that anybody who has to make an important decision - especially one of life and death - at times of stress - should wait to see the trend of changes, process the risks and chances in depth and only then decide."
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