Evolution of new metabolic pathways and microbial communities

The evolution of metabolic pathways in microbes is traditionally envisioned to take place within a single organism. The diverse repertoire of enzymes in the microbial community points to another exciting possibility: namely, that new metabolic pathways may evolve in a community setting, where pathway steps are distributed across several strains. The readiness with which microbes form stable relationships to collectively degrade manmade ‘xenobiotic’ pollutants, as evidenced from natural and laboratory-enriched consortia, provides valuable insights into the evolution of enzymes and pathways. Nonetheless, many open questions remain to be addressed. In this review, we consider the key determinants of pathway evolution in microbial communities, drawing from principles of social evolutionary theory in microbes, and also exploring the role of diffusion and horizontal gene transfer.