Background/Question/Methods: A typical gram of soil contains on the order of a billion cells, which have been shown to represent about a million different genomes. Is this remarkable level of coexisting diversity of microbes largely due to an unappreciated diversity of distinct resources and spatial heterogeneity, or because of a tangled bank of biotic interactions? Microbial interactions are widespread; however, the various factors that lead to the emergence of phenomena such as cooperation and co-evolution are unclear. I will describe the development of synthetic multi-species consortia as models for the examining the physiology and ecology of growth, and how these evolve under different environmental regimes.

Results/Conclusions:

A mutualism comprised of Methylobacterium and Escherichia coli has been shown to be maintained in co-culture that requires Methylobacterium to provide N to E. coli in return for C. The dynamics of this consortium are stable over the initial few growth cycles, but they quickly change due to adaptation. In liquid medium, we have observed the emergence of floating mixed biofilms that hold the partners in close proximity. Furthermore, preliminary work has suggested the emergence of cheaters within each species that are less competent in participating in the consortia than the ancestral strain. This work has opened the door to uncovering the physiological and genetic changes that occur during adaptation in a defined a mutualism, provides a test-bed for comparing experimental results to computational predictions based on models of cellular metabolism, and is an opportunity to test theory relating to the role of spatial structure and the size of interaction groups in promoting the emergence of increased cooperation.