Microbial communities play an essential role in biogeochemical cycles, local ecosystems, and human health. The study of microbial communities is also useful for theoretical ecology: As the simplest form of life demonstrating complex emergent properties, microorganisms enable the study of the “ecology of the possible.” Microbial communities demonstrate huge diversity, with 1 gram of soil containing up to 1 million bacterial species. Yet most microbial species cannot be cultured, suggesting microbial communities in situ are characterized by obligate interactions. One of the most widespread observed obligate interactions is syntrophy, where one species consumes the (often toxic) products of another species.
I constructed an evolutionary model composed of an artificially generated chemistry, an initial food set, three initial species (defined functionally) capable of performing certain reactions, a fast dynamics for reaching steady state, and a slow dynamics of mutation, and ran a simulation. The model is deliberately simplified in some respects while being realistic in other respects, with the intention of identifying the minimum necessary conditions for the evolution of syntrophic mutualisms.
Results/Conclusions
Starting from just three resources in the food set and three species, a community of many mutually interdependent species evolves through a process of successive niche construction, with most species unable to survive independently. This only occurs when there is a mechanism for the temporary partial removal of toxic compounds from the local environment; for example, through diffusion. Crucially, the emergence of these obligate mutualisms occurs without requiring cooperation. Furthermore, preliminary results suggest particular constraints and inherent trade-offs in the space of possible reactions, such as the necessity of producing toxic waste products from some reactions contributing to growth, are crucial to enabling the evolution of syntrophic mutualisms. This suggests that inefficiencies in the processes by which the available resource pool is converted into energy may be a necessary condition for the evolution of obligate mutualisms and resulting diversity.