Vegetative cell fusion and a new stage in the life cycle of the Aphelida (Opisthosporidia)

Abstract

The aphelids, intracellular parasitoid of algae, play signi cant role in the ponds communities regulating the algae blooms. They represent a large cluster of OTUs sister to Fungi at the molecular phylogenetic tree sharing a common ancestor with fungi. Their vegetative life cycle being similar to that of chytridiomycetes includes opisthokont uni agellar zoospores, cysts, phagotrophic intracellular stage, and multinuclear plasmodium producing zoospores. The sexual part of life cycle is not known, and, as we can see now, the asexual part is also understudied. We have found in the Aphelidium insulamus and other ahelid species a new stage -big multi agellar, or amoeboid cells, which can be considered both, the result of zoospore fusion, or the remnant of plasmodium after zoospore formation. A study of this phenomenon lead us to the conclusion, that after multicellular infection the trophic stages of different parasitoids fuse in one plasmodium having different sorts of nuclei. Some of them become the nuclei of zoospores, while the others left in the remnant of plasmodium, which becomes a monster. The families of protein encoded genes involved in the vegetative cell fusion was also discussed.

Study of a new strain of Sanchytrium tribonematis expands our knowledge on Sanchytriomycota (Fungi)

“…From this point, we can try to explain a phenomenon of multiple kinetosomes in big zoospores of S. tribonematis, which were found for the rst time and not studied yet in details. Two types of zoospores were also shown for the aphelids (Tcvetkova et al, 2023). Big amoeboid zoospores with 2-4 nuclei have been found in the culture Amoeboaphelidium protococcorum (Gromov & Mamkaeva, 1968) and big zoospores with 3-12 stiff agella described recently in Aphelidium insulamus (Tcvetkova et al, 2023).…”

“…Two types of zoospores were also shown for the aphelids (Tcvetkova et al, 2023). Big amoeboid zoospores with 2-4 nuclei have been found in the culture Amoeboaphelidium protococcorum (Gromov & Mamkaeva, 1968) and big zoospores with 3-12 stiff agella described recently in Aphelidium insulamus (Tcvetkova et al, 2023). The authors supposed that such big cells can be a result of incomplete plasmodium division and probably do not survive.…”

Marine parasite Protaphelidium rhizoclonii gen. et sp. nov. designates the basal environmental cluster at the aphelid phylogenetic tree

“…This way of penetration was described for all known aphelids and studied with TEM (Schnepf et al 1971; Karpov and Paskerova 2020). Perhaps, further fusion of two trophonts occurs to produce a single plasmodium, as it was discussed recently for aphelids (Tcvetkova et al 2023). That suggests a common phenomenon for aphelids.…”