Phylogenetic analysis of pathogenic algae reveals lineage-dependent patterns of phagocytosis

Protothecosis is a rare algal infection caused by members of the genus <i>Prototheca</i>, which is comprised of unusual non-photosynthetic algae. Six pathogenic species have been identified so far that can cause infection in vertebrates, primarily cattle and humans. The phylogeny of this genus remains obscure and has been revised multiple times recently. However, this phylogeny has largely been based on only three species of <i>Prototheca</i>. To resolve this phylogenetic conundrum, here, we employ a phylogenetics approach based on five new organelle-encoded genes. We then use these data to perform live-cell imaging of a selected range of <i>Prototheca</i> species co-cultured with mammalian immune cells. Visualizing these phagocytic interactions in this context helps delineate both host cell-type- and species-dependent differences in phagocytic uptake, thereby providing novel insight into lineage-based differences.