Txikispora philomaios n. sp., n. g., a Micro-Eukaryotic Pathogen of Amphipods, Reveals Parasitism and Hidden Diversity in Class Filasterea

Ander Urrutia, Konstantina Mitsi, Rachel Foster, Stuart Ross, Martin Carr, Georgia Ward, Ronny van Aerle, Ionan Marigomez, Michelle Leger, Iñaki Ruiz-Trillo, Stephen Feist, David Bass

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Abstract

This study provides a morphological, ultrastructural, and phylogenetic characterization of a novel micro-eukaryotic parasite (2.3–2.6 µm) infecting amphipod genera Echinogammarus and Orchestia. Longitudinal studies across two years revealed that infection prevalence peaked in late April and May, reaching 64% in Echinogammarus sp. and 15% in Orchestia sp., but was seldom detected during the rest of the year. The parasite infected predominantly hemolymph, connective tissue, tegument, and gonad, although hepatopancreas and nervous tissue were affected in heavier infections, eliciting melanization and granuloma formation. Cell division occurred inside walled parasitic cysts, often within host hemocytes, resulting in hemolymph congestion. Small subunit (18S) rRNA gene phylogenies including related environmental sequences placed the novel parasite as a highly divergent lineage within Class Filasterea, which together with Choanoflagellatea represent the closest protistan relatives of Metazoa. We describe the new parasite as Txikispora philomaios n. sp. n. g., the first confirmed parasitic filasterean lineage, which otherwise comprises four free-living flagellates and a rarely observed endosymbiont of snails. Lineage-specific PCR probing of other hosts and surrounding environments only detected T. philomaios in the platyhelminth Procerodes sp. We expand the known diversity of Filasterea by targeted searches of metagenomic datasets, resulting in 13 previously unknown lineages from environmental samples.

Original languageEnglish
Article numbere12875
Number of pages25
JournalJournal of Eukaryotic Microbiology
Volume69
Issue number2
Early online date2 Nov 2021
DOIs
Publication statusPublished - 1 Mar 2022

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