Speaker
Description
Endosymbioses have significantly changed the course of life on Earth, by giving rise to energy-producing organelles such as mitochondria and chloroplasts. While common in eukaryotes, endosymbiosis is extremely rare in bacteria, with only a handful of known instances. This rarity is shocking given the tremendous diversity and abundance of bacteria. While many factors may contribute to their rarity, we lack quantitative methods for estimating the extent to which these factors constrain the emergence of bacterial endosymbiosis. Here we assess several proposed constraints using a combination of mathematical approaches, including dynamical systems, metabolic models, and allometric scaling relationships. In the absence of direct empirical evidence, these models provide null predictions for the expected frequency of bacterial endosymbioses. We show that the initial formation of endosymbioses is not limited by internal spatial constraints within bacteria, ecological interactions between species, or the coupling of host–endosymbiont metabolisms. However, we identify potential conflicts involving growth-rate synchronization and evolvability that can destabilize early endosymbioses and lead to their extinction. Together, these results demonstrate how mathematical modeling can help identify the dominant constraints on the emergence of bacterial endosymbiosis.
