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.

中文翻译：

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apicomplexan Cardiosporidium cionae中的alphaproteobacterial内共生体的代谢贡献。

蚜复合体是多种多样的原生动物门，几乎完全由感染后生动物的寄生虫组成，包括疟疾，隐孢子虫病和弓形虫病的病原体。单一的蜂复合体属肾病（Nephromyces）在2010年被描述为其被膜宿主的互惠伴侣。在这里，我们介绍了从寄生姊妹物种到这种互惠生菜Cardiosporidium cionae及其相关细菌内共生体的基因组和转录组数据。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，垂直传播α-变形菌已被保留在每个谱系因为Nephromyces和Cardiosporidium发散。这种β-细菌内共生体具有大大降低的代谢能力，但对C. cionae贡献了必需的氨基酸赖氨酸和必需的辅因子硫辛酸。这种伙伴关系可能会减少与被告主持人的资源竞争。但是，我们的数据表明，单个𝝰-proteobacterial内共生在C. cionae相比三个类群中存在的内共生菌的最小Nephromyces系统，并且是用于这些谱系之间的毒力视差可能的解释。