Syntrophic exchange in synthetic microbial communities

Significance Metabolic exchange between microbes is a crucial process driving the development of microbial ecosystems. The exchange of essential amino acids presents an opportunity to investigate the guiding principles underlying microbial trade in nature. In this study, we devised synthetic communities of Escherichia coli bacteria of increasing complexity to measure general properties enabling metabolic exchange of amino acids. We identified numerous syntrophic interactions that enable cooperative growth, which exhibited both positive and negative epistasis with increasing community complexity. Our results suggest that amino acid auxotrophy may be an evolutionarily optimizing strategy to reduce biosynthetic burden while promoting cooperative interactions between different bacteria in the microbiome.