Apicomplexa is a group of unicellular organisms that has been long been considered an exclusively parasitic clade. There are many ecologically and medically important apicomplexans, including the causative agent of malaria. However, recent evidence has revealed one group of mutualistic apicomplexans: the marine symbiont genus, Nephromyces. Nephromyces are unusual apicomplexans in many ways. First, members of this genus are found exclusively inside one family of sea squirts, where they colonize a large, ductless organ, the renal sac. Within this organ, Nephromyces surround urate and calcium oxalate deposits. Second, unusually for apicomplexans, Nephromyces cells contain intracellular bacteria. This mutualistic apicomplexan offers a singular opportunity to address the important question about apicomplexan biology. With a long-term goal of completely characterizing this system, here we propose to focus on comparing the Nephromyces genome to its closest relative, the parasitic genus, Cardiosporidium. Members of Cardiosporidium parasitize a broad range of sea squirts yet, like Nephromyces, also contain endosymbiotic bacteria. The genomes of the bacteria inhabiting both Nephromyces and Cardiosporidium will also be sequenced. Data generation will have an emphasis on the hypothesis that the bacterial symbionts may provide key metabolic functions in the evolution of this mutualism. The genome sequences from these organisms will provide a stepping-stone for cytological, microscopy and functional genomic research. Understanding the genomic signatures of lifestyle transitions in Apicomplexa will have significant impact on determining which, as yet underappreciated, genomic features are correlated with virulence and parasitism.
Apicomplexans include the most medically important human parasites on Earth, most notably as the causative agent of malaria. The proposed research will explore the genome of the only apicomplexan that has switched from a parasitic lifestyle, to a mutualistic one. The data generated by this research will facilitate a re-examination of genes involved in malarial virulence by direct comparison to a non-pathogenic relative.
