Rediscovery of an unusual chytridiaceous fungus new to the order Rhizophydiales

The new chytridiomycete Paradinomyces triforaminorum gen. et sp. nov. co-occurs with other parasitoids during a Kryptoperidinium foliaceum (Dinophyceae) bloom in the Baltic Sea

A new chytrid genus and species was isolated and cultured from samples obtained in the Baltic Sea during a dinoflagellate bloom event. This species is characterized by having a spherical sporangium without papillae and zoospores of 2-3 µm in diameter that are released through 3 discharge pores. Molecular phylogeny based on ribosomal operon showed its sister position to the Dinomyces cluster in Rhizophydiales. Zoospores lack fenestrated cisternae but contain a paracrystalline inclusion, found in a Rhizophydiales representative for the first time. Additionally, the kinetid features are uncommon for Rhizophydiales and only observed in Dinomyces representatives so far. These morphological features and its phylogenetic relationships justify the description of the new genus and speciesParadinomyces triforaminorum gen. nov. sp. nov. belonging to the family Dinomycetaceae. The chytrid was detected during a high-biomass bloom of the dinoflagellate Kryptoperidinium foliaceum. Laboratory experiments suggest this species is highly specific and demonstrate the impact it can have on HAB development. The chytrid co-occurred with three other parasites belonging to Chytridiomycota (Fungi) and Perkinsea (Alveolata), highlighting that parasitic interactions are common during HABs in brackish and marine systems, and these multiple parasites compete for similar hosts.

A new family and four new genera in Rhizophydiales (Chytridiomycota)

Many chytrid phylogenies contain lineages representing a lone taxon or a few organisms. One such lineage in recent molecular phylogenies of Rhizophydiales contained two marine chytrids, Rhizophydium littoreum and Rhizophydium aestuarii. To better understand the relationship between these organisms, we increased sampling such that the R. littoreum/R. aestuarii lineage included 10 strains of interest. To place this lineage in Rhizophydiales, we constructed a molecular phylogeny from partial nuc 28S rDNA D1-D3 domains (28S) of these and 80 additional strains in Rhizophydiales and examined thallus morphology and zoospore ultrastructure of our strains of interest. We also analyzed sequences of the nuc rDNA region encompassing the internal transcribed spacers 1 and 2, along with the 5.8S rDNA (ITS) of our 10 strains of interest to assess sequence similarity and phylogenetic placement of strains within the lineage. The 10 strains grouped together in three well supported clades: (i) Rhizophydium littoreum+Phlyctochytrium mangrovei, (ii) three strains of Rhizophydium aestuarii and (iii) five previously unidentified strains. Light microscopic observations revealed four distinct thallus morphologies, and zoospore ultrastructural analyses revealed four distinct constellations of ultrastructural features. On the bases of morphological, ultrastructural and molecular evidence we place these strains in the new family Halomycetaceae and four new genera (Halomyces, Paludomyces, Ulkenomyces, Paranamyces) in Rhizophydiales.