Molecular Phylogeny and Ultrastructure of Aphelidium aff. melosirae (Aphelida, Opisthosporidia)

Abstract

Aphelids are a poorly known group of parasitoids of algae that have raised considerable interest due to their pivotal phylogenetic position. Together with Cryptomycota and the highly derived Microsporidia, they have been recently re-classified as Opisthosporidia, being the sister group to fungi. Despite their huge diversity, as revealed by molecular environmental studies, and their phylogenetic interest, only three genera have been described (Aphelidium, Amoeboaphelidium, and Pseudaphelidium), from which 18S rRNA gene sequences exist only for Amoeboaphelidium species. Here, we describe the life cycle and ultrastructure of Aphelidium aff. melosirae, and provide the first 18S rRNA gene sequence obtained for this genus. Molecular phylogeny analysis indicates that Aphelidium is very distantly related to Amoebaphelidium, highlighting the wide genetic diversity of the aphelids. The parasitoid encysts and penetrates the host alga, Tribonema gayanum through an infection tube. Cyst germination leads to a young trophont that phagocytes the algal cell content and progressively develops a plasmodium, which becomes a zoospore-producing sporangium. Aphelidium aff. melosirae has amoeboflagellate zoospores, tubular/lamellar mitochondrial cristae, a metazoan type of centrosome, and closed orthomitosis with an intranuclear spindle. These features together with trophont phagocytosis distinguish Aphelidium from fungi and support the erection of the new superphylum Opisthosporidia as sister to fungi.

Molecular Phylogeny of Paraphelidium letcheri sp. nov. (Aphelida, Opisthosporidia)

“…nov. 18S rDNA sequence was aligned with a collection of sequences of available aphelids and other opisthokonts as previously used in Karpov et al. () and Letcher et al. () using Mafft (Katoh et al.…”

“…melosirae P‐1 CALU (Karpov et al. ) and three strains of the recently described genus and species Paraphelidium tribonemae (Karpov et al. ).…”

Novel Diversity of Deeply Branching Holomycota and Unicellular Holozoans Revealed by Metabarcoding in Middle Paraná River, Argentina

“…With regards Holomycota, we built a reference tree including the main lineages of Fungi, Opisthosporidia and unicellular clades of Holomycota, together with environmental sequences (Karpov et al, 2014b;Richards et al, 2015) (Supplementary Datasheet 1). We then performed a phylogenetic placement of all Holomycota OTUs into this curated reference tree using pplacer package (Matsen et al, 2010).…”

Microsporidia: Eukaryotic Intracellular Parasites Shaped by Gene Loss and Horizontal Gene Transfers

“…Cryptomycota is a recently erected phylum composed of a variety of lineages and is now thought to include the basal fungus R. allomycis, the algal parasites aphelids, and the Microsporidia (4,39,41,42,57). The first major support for an evolutionary link between the Microsporidia and the Cryptomycota followed publication of the R. allomycis genome (39).…”