Solving an old enigma: Morellospora saccamoebae gen. nov., sp. nov. (Rozellomycota), a Sphaerita-like parasite of free-living amoebae.

The Rozellomycota form a lineage basal or sister to the Fungi, ancestor of Microsporidia. Their biodiversity is very rich but remains poorly characterized. The few known species are all parasites, whether of water molds and algae (Rozella), crustaceans (Mitosporidium), or as endonuclear parasites of amoebae (Nucleophaga, Paramicrosporidium). Since the nineteenth century, intracytoplasmic parasites of various protozoa have been described as species of the same genus Sphaerita. However, it was later thought possible to separate these parasites into at least two distinct groups, those forming flagellated zoospores, prevalent in Euglena and other flagellates, and those forming immobile spores, found mainly in free-living and endozoic amoebae. Herein, we report the recovery of a strain of the free-living amoeba species Saccamoeba lacustris, naturally infected by an intracytoplasmic parasite, which under light microscope has a morphology consistent with that of Sphaerita. Biomolecular analyses were thus performed. Our results show that the intracytoplasmic parasite of Saccamoeba belongs to the same subgroup of Mitosporidium and that it forms a new genus within Rozellomycota, Morellospora, that corresponds to the former spore-forming Sphaerita-like parasites of amoebae.