Proposal of Monorhizochytrium globosum gen. nov., comb. nov. (Stramenopiles, Labyrinthulomycetes) for former Thraustochytrium globosum based on morphological features and phylogenetic relationships

Abstract

SUMMARY Thraustochytrium is the type genus of the family Thraustochytriaceae in the class Labyrinthulomycetes. This genus is characterized by zoospore formation, namely, shape of the cell wall of sporangia and presence or absence of a proliferous body. However, there are several issues associated with the taxonomy of this genus, and these include polyphyletic taxa and overlapping of taxonomic features among species. In particular, the first and second species, T. proliferum and T. globosum, were described based on observations of the morphological features of natural samples in the absence of culture conditions. Before addressing the taxonomic issues associated with this genus, it is important to consider the taxonomic features of each species, i.e., the life history under culture conditions and the phylogenetic position. The objective of the present study was to isolate T. globosum, the second described species in the genus Thraustochytrium, from the type locality. We successfully isolated strain NBRC 112723, which exhibited characteristic features of T. globosum. Under culture conditions, strain NBRC 112723 exhibited taxonomic features observed in other thraustochytrid species. Our molecular phylogeny indicated that this strain isolated from the type locality was located in an unidentified thraustochytrid group; moreover, some strains located in this group exhibited characteristic features of strain NBRC 112723. We clearly distinguished T. globosum based on the taxonomic criteria used to classify the T. proliferum type species. Therefore, we propose the establishment of a new genus, Monorhizochytrium, for the species T. globosum in the family Thraustochytriaceae.

Nutritional intake of Aplanochytrium (Labyrinthulea, Stramenopiles) from living diatoms revealed by culture experiments suggesting the new prey–predator interactions in the grazing food web of the marine ecosystem

“…This group is characterized by the presence of the ectoplasmic net system, which is produced by a unique organelle known as the bothrosome [2, 8–12]. The Labyrinthulea comprises at least four phylogenetically distinct groups [2, 5, 13–17]: the labyrinthulids are classified as Labyrinthula spp., whose spindle-shaped cells are located in the ectoplasmic net element; the thraustochytrids account for almost all genera whose spherical cells have rhizoid-like ectoplasmic nets produced from a single bothrosome; the oblongichytrids are classified as Oblongichytrium spp., which are characterized by slender oblong zoospores; and the aplanochytrids are classified as Aplanochytrium spp., which form hexagonal scaly walled sporangia that release non-flagellate gliding cells known as aplanospores.…”

Occurrence of Thraustochytrids on fallen mangrove leaves from Pagbilao Mangrove Park, Quezon Province

“…The cells exhibited partitioning from a central point, rather than the release of amoeboid or zoosporic cells; moreover, their ectoplasmic nets were also inconspicuous. These observations along with that of the colonial features pointed to the morphologically similar genera Aurantiochytrium, Hondaea or Monorhizochytrium as a (Dellero et al, 2018;Doi & Honda, 2017;Yokoyama & Honda, 2007).…”

Isolation and transcriptome analysis of a biotechnologically promising Black Sea protist, Thraustochytrium aureum ssp. strugatskii

“…Taxonomy and phylogenetic relationships within Labyrinthulomycetes at the level of higher taxa are mostly resolved ( Tsui et al, 2009 ; Doi & Honda, 2017 ). At the lower taxonomic level, it is constantly refined with the emergence of new molecular data ( Bennet et al, 2017 ; Pan, Del Campo & Keeling, 2017 ).…”