Intra-host symbiont diversity and extended symbiont maintenance in photosymbiotic Acantharea (clade F)

In this study, we applied single-cell sequencing methods to investigate host-symbiont dynamics in clade F acantharians, a dominant group of photosymbiotic protists in oligotrophic subtropical gyres. We collected samples along the Ryukyu Archipelago in the East China Sea (Japan), which spans more than 1,000 km, and near Catalina Island (California, U.S.A). We then amplified the 18S rRNA gene from single acantharian hosts and seawater samples to determine the intra-host symbiont diversity and whether intra-host symbiont community compositions directly reflect the available symbiont community in the surrounding environment. Our results demonstrate that clade F acantharians simultaneously host multiple species from the haptophyte genera Phaeocystis and Chrysochromulina. The intra-host symbiont community composition was distinct from the external free-living symbiont community, suggesting that these acantharians maintain symbionts for an extended period of time.