Cryptomycetes

All described types of roselids are intracellular parasites or parasitoids. Representatives of the genus Rozella affect aquatic forms of fungi and oomycetes . The species R. coleochaetis was found in the green alga ^[6] . Paramicrosporidium and Nucleophaga infect representatives of amoebose , developing inside the nuclei of their hosts ^{[2] [7]} .

Among cryptomycete cells isolated from environmental samples using the TSA- FISH technique and not belonging to the described species, forms were found that formed associations with other organisms, primarily diatoms . The authors of this study suggested that these cryptomycetes can lead a free-living lifestyle ^[8] . However, it is possible that these cells are invasive cysts attached to the cells of the host body (this stage of the life cycle is typical for representatives of Rozella ) ^[2] .

Rosellids describe two fundamentally different variants of the life cycle . The first is characteristic of representatives of the genus Rozella : motile zoospores contact the host cell and encyst . The cyst forms a tube that grows into the host cell, as well as a large vacuole at the posterior end. Due to the expansion of the latter, the amoeboid protoplast of the parasite is introduced from the cyst into the infected cell. The parasite is actively growing and feeding, including through phagocytosis . Then, in the parasite cell, nuclear fission begins, and sporangia is formed, in which a large number of new zoospores are formed that enter the external environment to infect other cells or other individuals. In addition, some Rozella species can form resting spores designed to survive adverse conditions ^[6] .

Another life cycle variant is characteristic of representatives of the genera Paramicrosporidium and Nucleophaga . Fixed spores of parasites are phagocytosed by amoebae and invade the nuclei of the latter. Parasites actively grow and feed, after which they turn into unicellular sporangia, in which new spores form. Throughout the development of parasites, the amoeba’s nuclear membrane remains intact. After the entire core volume is occupied by parasites, the host cell is destroyed and spores exit into the external environment ^{[2] [7]} .

The size of the rosellide cells ranges from 1 to 10 micrometers , depending on the stage of the life cycle and species. All stages of the life cycle of Rozella , with the exception of mature resting spores, are devoid of chitinous cell walls and have a standard set of cellular organelles . Zoospores of Rozella carry a single flagellum located at the posterior end of the cell ^[6] . Spores of Paramicrosporidium and Nucleophaga are in many respects similar to spores of microsporidia , have an oval or round shape, are covered with chitin and protein membranes, are devoid of flagella and mitochondria . In Paramicrosporidium , structures were found that resemble the components of the microsporidium extrusion apparatus : polar filament and anchor disk ^[2] .

As of 2015, metabolic data are available only for the species Rozella allomycis , whose genome has been deciphered. The mitochondrial genome of this species demonstrates a significant degree of reduction and is represented by a ring molecule of about 12 thousand pairs of nucleotides encoding six proteins - components of the respiratory chain of electron transfer . Moreover, R. allomycis lacks complex I of this system. All components of the Krebs cycle were also found in the genome of this species, which indicates the ability of this organism to produce ATP using oxidative phosphorylation . Moreover, in R. allomycis , unique elements of the metabolic system characteristic of microsporidia were found: an alternative respiratory chain represented by the cytoplasmic and mitochondrial forms of NADH dehydrogenase and alternative oxidase , as well as nucleotide carriers used by microsporidia for direct ATP transport from the host cell cytoplasm ^{[ 9]} .

The genus Rozella was described in 1872 by the French botanist Maxim Cornu ^[11] . These organisms were considered chytrid fungi before the publication of the results of molecular-phylogenetic studies of Lara et al. 2010. The authors demonstrated that Rozella, together with the LKM11 clade, represented by sequences of genes isolated using metagenomic methods, forms a separate monophyletic taxon . The authors identified this clade as the most basal branch in the composition of mushrooms and gave it the name Rozellida ^[1] .

In 2011, Jones et al published a formal taxonomic description of this group, where they assigned it the type rank and name of Cryptomycota ^[5] . In 2013, James et al. Published the results of decoding the Rozella allomycis genome , where it was shown that cryptomycetes share many unique features with microsporidia (a group of intracellular parasites related to fungi), and it is microsporidia that are the closest relatives of rosellids ^[9] .

In 2014, Corsaro et al. Described a new type of cryptomycete: Paramicrosporidium , which is fundamentally morphologically different from Rozella and in many ways similar to microsporidia. Based on this, the authors gave a new taxonomic characterization of cryptomycetes, and also proposed a new name for the group: Rozellomycota ^[2] . In the same year, Karpov et al. Demonstrated that cryptomycetes together with microsporidia and aphelids (taxa related to fungi of alga parasitoids ) are sister groups and all three clades, in turn, form a sister taxon with respect to fungi ^{[10] [12]} .