By integrating with our Policy & Practices and the results from our wet lab experiments and modeling, iGEM2015 Team Tokyo_Tech have executed our project with improved design in accordance with comments from general public, and have strengthened the public engagement of a two-way dialogue between our team and the public through this summer. (See here to know how we integrated our project)

What is Prisoner’s Dilemma?

The Prisoner’s Dilemma game, a typical example analyzed in game theory, involves two prisoners who were given an option selection opportunity either to cooperate or to defect according to the payoff matrix (Fig.1-1-1) in order to pursue for the best profit. (Go to Project 1. page) In our project, we decided to replicate an E. coli’s version of Prisoner’s Dilemma payoff matrix (Fig.1-1-2), which punishment means growth inhibition of E. coli. (Go to Project 2. page)

Fig.1-1-1. The payoff matrix in Prisoner's Dilemma (punishment = imprisoned years)	Fig.1-1-2. Our replicated payoff matrix for growth inhibition effect on prisoner coli

Project Overview

Like the prisoners in the Dilemma game, we genetically engineered two E. coli acting as Prisoner A and Prisoner B, which are able to cooperate or to defect in our E. coli’s version of Prisoner Dilemma. The combinations of their option (cooperation or defection) affect their profit which equals to their growth. To cooperate, they produce AHL while to defect, they do not produce AHL. The act of producing AHL imposes a metabolic burden on a prisoner coli. Furthermore, chloramphenicol antibiotic is used to inhibit prisoner coli’s growth in culture. However, AHL produced by the cooperation induces of the opponent prisoner, so that the expression of chloramphenicol resistant gene circumvents the growth inhibition effect.
(Go to Project 3. page)

Fig.1-1-3. The genetic circuits of prisoner coli with the options of cooperation or defection

Fig.1-1-4. Growth inhibition experienced by prisoner coli as a result of combination of option

Suggestion from modeling allowed us to successfully construct an improved part for precise implementation of our payoff matrix, when initial designed circuits showed leaky expression of CmR at the first stage of our experiment. This is one of engineering principle in our iGEM activity.
(See here for more modeling results)

Fig.1-1-5. Suggestions from modeling allow us improving a previously existing part

Using the improved plasmids we constructed to decrease effect of leaky expression, our E. coli version of payoff matrix is successfully replicated through wet lab experiments (Fig.1-1-6). In our payoff matrix, with the combination of four options between two prisoner coli, we succeeded to replicate four types of growth inhibition: none, low, middle, and high.
(See here for more details on our wet lab experiments)

Fig.1-1-6. The results from our wet lab replicated the payoff matrix

In order to enable prisoner coli to select its option randomly between cooperation and defection, we showed bidirectional inversion of Fim switch by FimB recombinase (BBa_K1632010). In our knowledge, this is the first case in iGEM to show random inversion of a promoter.
(See here to know more on how prisoner coli decides)
(See here to know more detail of FimB experiment results)

Fig.1-1-7. (A) FimB allows Decision making coli to select option at random, inverting a promoter in a fim switch (B) The intensity of fluorescence in cells mrasured using flow cytometer (C) Colony formation using plasmid mixture extrarcted cell expressing FimB

Our game design allows E. coli to realize one of four strategies including tit-for-tat strategy (Fig.1-1-8), the most successful strategy for Prisoner’s Dilemma. For implementation of this strategy, we confirmed unidirectional inversion of a fim switch by the FimE recombinase.
(See here to know on how we designed our parts)
(See here to know more detail of FimE experiment results)

Fig.1-1-8. Prisoner A with tit-for-tat strategy in our iterated game

For integration of concerns we have met through interactions with general public, about gene modification issues into our project, we designed and executed an expanded Prisoner’s Dilemma game played by the high school and undergraduate students. We found not only biased decision resulting from unconscious impression associated with the term “GMO”, but importance of reflecting on our iGEMer’s own conception of risks and cost & benefit by establishing a two-way dialogue.
(See here for more details)

Fig.1-1-9. Overall results of our expanded dilemma game among students