Use of game-theoretical approaches in Systems Biology

Game theory can be considered as an extension of the theory of optimization. In biological appications, it can describe situations where two or more organisms (or more generally, units of replication) tend to optimize their properties in an interdependent way. Thus, the outcome of the strategy adopted by one species depends on the strategy of the other species. In this talk, the use of evolutionary game theory for analysing intracellular (e.g. metabolic) networks is outlined. The presentation is illustrated by a number of instructive examples such as the competition between micro-organisms using different metabolic pathways for synthesizing ATP and the secretion of extracellular enzymes or toxins. These examples show that, due to conflicts of interest, the global optimum (in the sense of being the best solution for the entire system) is not always obtained. For example, some yeast species use metabolic pathways that waste the nutrient. A particularly interesting game is the Prisoner’s Dilemma, in which cooperation is unstable due to the tendency of the “players” to increase their fitness, which leads to the counter-intuitive result of a decrease in the fitness of all “players”. Such situations of “arms race” are indeed found in biology, even at the level of biochemical pathways. In other situations or for other parameter values, also other types of game can be relevant, such as the snowdrift, rock-scissors-paper or harmony games. Since game theory takes into account the systemic interactions and can describe emergent properties, it is very promising for Systems Biology. It also has important applications in biotechnology. For example, it can be used for analysing whether exoenzyme producing strains will be outcompeted by cheater mutants.