Quantifying the energetic costs and growth benefits of phagocytosis

Phagocytosis, the ingestion of cells by other cells, is ubiquitous among eukaryotic life. It is utilized for food uptake and in the immune response in many species. The origin of phagocytosis and its role in the evolution of endomembranes and the eukaryotic cell remains obscure. Drawing on a wealth of empirical data, we integrate prey capture, engulfment, and internal and external digestion into a mathematical model that quantifies the cellular performance of a primitive phagocytoser relative to a non-phagocytosing ancestor. The primitive phagocytoser can outperform the ancestor in a range of situations. The rate of engulfment delineates when phagocytosis is advantageous, providing clear benchmarks for interpreting the importance of results in genetic knockout studies and mechanical models. The phagocytoser even outperforms the ancestor when food vacuoles cannot be recycled. The model suggests plausible waypoints for the evolution of phagocytosis and the eukaryotic endomembrane system.