Gromochytrium mamkaevae gen. & sp. nov. and two new orders: Gromochytriales and Mesochytriales (Chytridiomycetes)

Abstract

During the last decade several new orders were established in the class Chytridiomycetes on the basis of zoospore ultrastructure and molecular phylogeny. Here we present the ultrastructure and molecular phylogeny of strain x-51 CALU – a parasite of the alga Tribonema gayanum, originally described as Rhizophydium sp. based on light microscopy. Detailed investigation revealed that the zoospore ultrastructure of this strain has unique characters not found in any order of Chytridiomycetes: posterior ribosomal core unbounded by the endoplasmic reticulum and detached from the nucleus or microbody-lipid complex, and kinetosome composed of microtubular doublets. An isolated phylogenetic position of x-51 is further confirmed by the analysis of 18S and 28S rRNA sequences, and motivates the description of a new genus and species Gromochytrium mamkaevae. The sister position of G. mamkaevae branch relative to Mesochytrium and a cluster of environmental sequences, as well as the ultrastructural differences between Gromochytrium and Mesochytrium zoospores prompted us to establish two new orders: Gromochytriales and Mesochytriales.

Phylogenetic Position of Parasitic Chytrids on Diatoms: Characterization of a Novel Clade in Chytridiomycota

“…), and the same is true of “Novel Clade I” (Karpov et al. ). In lakes in which environmental sequences of uncultured chytrids have been detected, such as Lake Aydat and Lake Pavin, various chytrids infecting algae were also confirmed by fluorescent microscopic observations (Jobard et al.…”

“…Karpov et al. () revealed that Mesochytrium penetrans Gromov parasitic on the green algae Chlorococcum minutum Starr belonged to “Novel Clade I (Jobard et al. ; Lefèvre et al.…”

“…; Karpov et al. ). This finding indicates that some of the novel clades are composed of parasitic chytrids that have been described, but not yet sequenced.…”

“…Although there are a large number of described species of parasitic chytrids (Sparrow ), only a few parasitic chytrid species have been sequenced and their phylogenetic positions clarified (Karpov et al. , ; Küpper et al. ; Lepelletier et al.…”

High-level classification of the Fungi and a tool for evolutionary ecological analyses

“…We also treat all former orders of Chytridiomycota at the class level (mean ages 330-420 Ma), viz. Chytridiomycetes, Cladochytriomycetes, Lobulomycetes, Mesochytriomycetes (comprising Mesochytriales and Gromochytriales), Polychytriomycetes, Rhizophlyctidomycetes, Rhizophydiomycetes, Spizellomycetes and Synchytriomycetes (James et al 2006b;Karpov et al 2014a;Seto et al 2017;. In the Blastocladiomycota, we accommodate the family Physodermataceae in class Physodermatomycetes, which is warranted by its distinct phytopathogenic mode of nutrition, early branching position and age (505 Ma; James et al 2006b;Porter et al 2011).…”