Identifying the lethal fish egg parasite lchthyodiniumchabelardi as a member of Marine Alveolate Group I

摘要

Cells of the parasitic, unicellular eukaryote lchthyod-inium chabelardi were isolated from eggs of sardine(Sardina pilchardus) and from a previously unrecog-nized host, bogue (Boops boops), off the Atlanticcoast of Portugal. Immediately after release from theinfected fish egg or newly hatched larva, I. chabelardicells were spherical and non-motile. After few minutes,spherical cells became flagellated and motile. Follow-ing 2-3 days of incubation and several divisions,spherical flagellated cells developed a twisted elon-gate shape and moved vigorously. Sequences of thesmall-subunit ribosomal RNA gene (SSU rDNA) wereidentical for L chabelardi of both hosts and so weresequences of ITS1, ITS2 and the 5.8S rRNA gene. Thisgenetic similarity suggests that eggs of sardine andbogue were infected by one single population of I. cha-belardi. The SSU rRNA gene sequence of I. chabelardiwas, in turn, 97% similar to those of two identical Asianisolates of lchthyodinium sp. Phylogenetic analysesshowed high support for the inclusion of lchthyod-inium in the so-called Marine Alveolate Group I (MAGI).Two morphologically well-described genera, namelylchthyodinium and Dubosquella, have now beenshown to belong to this group of seemingly exclu-sively parasitic alveolates.