Cryptomycota/Microsporidia

 Cryptomycota plus Microsporidia are sisters to the remaining lineages of Kingdom Fungi. (Note: Rozellomycota is another name for Cryptomycota based on the genus Rozella and the principle of autotypification. 

Cryptomyces is a genus in Ascomycota and cannot be used to typify Cryptomycota.) Cryptomycota consists of a handful of described taxa and taxa that are known only from environmental samples. One described taxon is Rozella, a biotrophic intracellular parasite of other zoosporic fungi of Chytridiomycota and Blastocladiomycota and oomycetes of the kingdom Stramenopila. 

There are few additionally described genera and species of Cryptomycota, but environmental sampling using molecular markers has revealed a phylogenetically diverse assemblage of fungi detected in soils, marine, and freshwater sediments, and oxygen-depleted environments. Some environmental Cryptomycota produces zoospores with a single, smooth flagellum, but chitin, a cell wall carbohydrate produced by most fungi, was not originally detected in the life history stages first observed. 

A more recent study detected chitin restricted to the cyst phase that attaches to the Allomyces hyphae and in the inner wall of the resting sporangia. 

The ecology of the environmental Cryptomycota is largely conjecture at this time because they have not been cultured, an observation frequently invoked in fungal systems to infer an obligate biotroph. Recently, molecular data have determined that Paramicrosporidium, non flagellated parasites of amoebae, and Amoeboaphelidium, an algal parasite, are members of Cryptomycota, lending support to parasitism as an ecological signature of the phylum.

Microsporidia are intracellular parasites of all major groups of animals. They are particularly well known from insects, crustaceans, and fish but are also known to occur in mammals, including humans.

Microsporidia produce unique spores that infect host cells through a harpoon-like organelle that pierces the host cell membrane and provides a conduit for the injection of the parasite’s cytoplasm. Once inside the host cell, a spore, which includes an inner chitin-containing wall, is ultimately formed. 

The phylogenetic affinity of Microsporidia has been difficult to determine, with past classifications placing it among the polyphyletic protists, and early multigene phylogenies placing it in different parts of the kingdom Fungi. 

Genome-scale phylogenies have also proven problematic due to highly reduced genomes and fast rates of nucleotide substitution, but multiple analyses have garnered increasing support for its close relationship to Cryptomycota. 

Comparative genomic analyses have demonstrated that both groups share genomic traits including a nucleotide transporter that Microsporidia use for obtaining ATP from their hosts. This phylogenetic placement of Microsporidia provides further evidence for the early origins of parasitism and more than one loss of the flagellum within the kingdom Fungi.