The bacteria's prisoner's dilemma

Politicians and economists should learn from the decision-making process of bacteria under stress conditions, a process described in a study by a group led by Prof. Eshel Ben Yaakov from Tel Aviv University, published yesterday (XNUMXnd) in the scientific journal PNAS

The decision-making process is always done under pressure. Everyone knows the need to try to postpone important decisions until the very last moment, but apparently there are creatures that do it better than us and that we have something to learn from them - the bacteria.

In an article published today (Monday) in the scientific journal PNAS (Records of the American National Academy of Sciences), Prof. Eshel Ben-Yaakov from the Raymond and Beverly Sackler School of Physics and Astronomy at Tel Aviv University and his colleagues from the Institute for Theoretical Biological Physics at the University of California at San- Be careful because even for bacteria life is complex and stressful at the same time. How do they deal with adversity?, can these coping strategies be described at the molecular level?

Bacteria live in large colonies where the number of bacteria may reach up to 100 times the number of people on Earth. The new research showed how in a stressed state the bacteria in the colony communicate through chemical messages as each bacterium undergoes a sophisticated decision-making process. A process in which he uses a complex network of genes and proteins to perform complex chance calculations using game theory.

Many bacteria respond to stress such as starvation, toxins, DNA damage, etc. by creating spores - dormant and very resistant versions of the bacteria that can develop and come to life when conditions change for the better. Over 500 genes are involved in this process, and in the tested bacteria - Bacillus subtilis, it lasts about ten hours. The process ends with the death of the mother cell when the original DNA of the bacterium breaks down, while its replication has been copied into a spore, a process that does not exist in higher beings - where there are only two options - life or death. However, a small part of the bacteria move to another state known as COMPTEENCTE (in free translation - ability). This is a kind of intermediate state where the DNA is wrapped in a shell that allows it to still absorb substances from the environment but they are not yet spores.

In such a case, they can absorb DNA of bacteria that have become spores and that have been dispersed in the environment and look for, for example, sequences resistant to antibiotics (if the infection was caused by antibiotics) or consume them as food (if the infection was caused by starvation). This intermediate state allows the few bacteria that have chosen it to survive even if the environment has not changed, and to immediately return to full life (including reproduction through replication) as soon as the conditions return to their normal state without having to become spores. The advantage of this situation is a quick return to normal, the disadvantage - death in case the conditions do not improve is final and the DNA of the bacteria is lost forever.

The bacteria do have a problem, if they don't admit it (or in their case go into a 'capacity' state) they may on the one hand regain life if the conditions improve, while in the meantime they feed on the remains of their friends who decided to become spores, and on the other hand die for good if their friends don't become spores and everyone decides on a state ability or if the food will not be enough and the conditions of oppression will increase. Indeed, the research shows that only about 10% of the bacteria choose this state.

And this is where game theory comes into play, and especially a simple game within it - the prisoner's dilemma. The classic prisoner's dilemma is usually told about two prisoners who are given an offer - if one of them confesses to a crime and the other doesn't, the one who confessed will get 6 years in prison and the one who didn't will get 4 years in prison. If they both confess - they will get XNUMX years, and if neither of them confess, they will both go free. Apparently the temptation is not to confess, but it is impossible to know whether the other confessed, and thus the prisoner who did not confess meant that he spent more time in prison.

Unlike the usual prisoner's dilemma where there are two participants, in the game theory of bacteria the number of participants can be up to 100 times the number of people on Earth. And secondly - they have a limited time to make the decision.

"Here it's a more complex prisoner's dilemma," says Prof. Ben-Yaakov, each bacterium has to decide whether to cooperate (so that they will all become spores) or not to cooperate (state of ability) and profit, but different from the prisoner's dilemma test, here there is a ticking clock. They have an internal clock from a timer that measures how long they have until they make the decision to become a spore or not, depending on the strain and chemical messages they receive from other bacteria.

While making the decision, each bacterium sends messages to the environment that says what its intentions are - if it intends to form (produce a spore) or competence (ability) and examines what the intentions of other bacteria are and what their resistance is. Then he decides whether he goes into ability mode or tries to produce a spore. According to Prof. Ben Yaacov the bacteria usually do not deceive their friends and inform them by chemical means if they become a spore or pass into a state of competence, therefore the cheaters have a chance to beat the system. In addition, bacteria that do not want to cheat, delay their decision with a timer (whose duration depends on the intensity of the stress and may change if the stress gets worse or easier), and in the end see what their friends have decided. In the new article, a model is presented that deciphers how the bacteria use networks of genes and proteins used to calculate risks and the principles of game theory according to which they operate.

A similar dilemma is facing many citizens today who are asking whether or not to vaccinate against swine flu due to rumors that the side effects of the vaccine are dangerous. For example, it was said that the government would have required everyone to get vaccinated within a month. If everyone gets vaccinated, maybe we shouldn't get vaccinated so as not to suffer the side effects (assuming there are any) because anyway the disease will be stopped before it reaches us?

In this month we must learn about the intention of the other residents near us. The level of harassment in this case is the number of patients in our environment. The higher this number, the more inclined to make a decision to get vaccinated. On the other hand, for the same reason, more people around us will decide to get vaccinated, and then again it might be better not to get vaccinated because the morbidity will be curbed. If we were bacteria, we would compare the number of infected and the rate of vaccinations, and optimize.

"What we showed in this article is how the bacteria do this complex calculation and according to what principles. , we learned a simple rule - anyone who is required to make a decision in a time of pressure, especially a life and death decision, it is better to wait, check the trends of change, study in depth the chances and risks for the long term and only then react." Prof. Ben-Yaakov summarizes.

Written by Avi Blizovsky