Apicomplexa is a diverse protistan phylum composed almost exclusively of metazoan-infecting parasites, including the causative agents of malaria, cryptosporidiosis, and toxoplasmosis. A single apicomplexan genus, Nephromyces, was described in 2010 as a mutualist partner to its tunicate host. Here we present genomic and transcriptomic data from the parasitic sister species to this mutualist, Cardiosporidium cionae, and its associated bacterial endosymbiont. Cardiosporidium cionae and Nephromyces both infect tunicate hosts, localize to similar organs within these hosts, and maintain bacterial endosymbionts. Though many other protists are known to harbor bacterial endosymbionts, these associations are completely unknown in Apicomplexa outside of the Nephromycidae clade. Our data indicate that a vertically transmitted α-proteobacteria has been retained in each lineage since Nephromyces and Cardiosporidium diverged. This α-proteobacterial endosymbiont has highly reduced metabolic capabilities, but contributes the essential amino acid lysine, and essential cofactor lipoic acid to C. cionae. This partnership likely reduces resource competition with the tunicate host. However, our data indicate that the contribution of the single α-proteobacterial endosymbiont in C. cionae is minimal compared to the three taxa of endosymbionts present in the Nephromyces system, and is a potential explanation for the virulence disparity between these lineages.

蚜虫复合体是多种原生动物门，几乎完全由感染后生动物的寄生虫组成，包括疟疾，隐孢子虫病和弓形体病的病原体。一个单一的apicomplexan属，肾菌，在2010年被描述为被告主持人的互助伙伴。在这里，我们介绍了从寄生姐妹物种到这个互惠生的基因组和转录组数据，心脏孢子虫，及其相关的细菌内共生体。 心脏孢子虫 和 肾菌两者都感染被膜虫宿主，定位于这些宿主内的相似器官，并维持细菌内共生菌。尽管已知许多其他生物都有细菌内共生体，但在肾菌科以外的蚜虫复合体中这些关联是完全未知的。我们的数据表明，自从肾菌 和 心脏孢子发散。这种α-蛋白细菌内共生体的代谢能力大大降低，但有助于必需氨基酸赖氨酸和必需辅因子硫辛酸的代谢。纤毛虫。这种伙伴关系可能会减少与被告主持人的资源竞争。然而，我们的数据表明单个α-蛋白细菌内共生在纤毛虫 与存在于内共生菌的三个类群相比是最小的 肾菌 系统，并且可以解释这些血统之间的毒力差异。