Designation of phylum cryptomycota within kingdom fungi Introduction The cryptomycota are considered to be to be an early branching clade of organisms, the only known members are species that belong in the genus Rozella (Lara et al 2010, Jones et al 2011, James and Berbee 2012). It has been suggested due largely to the amount of environmental sequences collected the phylum may be as diverse as the whole kingdom fungi (Jones et al 2011).While Rozella were originally placed in the fungal phylum Chytridiomycota(Jones and Pang 2012), a multi-gene molecular phylogeny of the Chytridiomycota found Rozella was in fact part of a separate linage considered to be the most basal lineage within the fungal kingdom (James et al 2006).
Analysis of environmental DNA samples based on the analysis of SSU RNA (small subunit ribosomal RNA genes)had revealed 26 sequences, previously unknown, which clustered closely to two species of Rozella included in the survey (Lara et al 2010).Lara et al tentatively named this clade ‘Rozedilla’ (Lara et al 2010, Jones et al 2011). However this clade was expanded to include 40 sequences found in marine and freshwater environments. This clade was renamed cryptomycota to reflect the position of the group relative to the fungi and its mostly hidden nature, as a large number of the phylum are only known from SSU RNA environmental surveys and their similarity in morphology and life-cycle to the Rozella is unknown (Jones et al 2011).Cryptomycota cells from freshwater samples, most notably from the Washington Singer pond (Exeter University, Devon, UK, 50. 7339uN, 3.
5375uW), were visualised with fluorescence in situ hybridization techniques. These target cells were shown to be small eukaryotes 3 to 5 ? meters in length (Jones et al 2011). Counter-staining with TAT1 tubulin revealed The target cells capable of forming a microtubule based flagellum (see fig 1)(Jones et al 2011). Chitin was not found in any of the morphs observed, this was tested by co-staining with cell wall markers (calcofluor white and lectin wheat germ agglutinin).Cellulose was also not present (Jones et al 2011). FIG 1: Micrographs showing flagella on cryptomycota cells, as detected by TAT1 tubulin antibody(Jones et al 2011) This study led Jones et al to the conclusion that the Cryptomycota were an intermediate group between fungus and protists. Others such as James and Berbee contend that ”they may have lost their “dinner jacket” through convergence. Rather than evolutionary intermediates, the cryptomycota may be strange, divergent fungi ” (James and Berbee 2012).
The term ”dinner jackets” here refers to cell walls. Some such as Griffith, Voight and Kirk would not consider the phylum fungal, but a non fungal opisthkonta like the Microsporidia(2011). In this essay I intended to explore the evidence both for and against the inclusion of the phylum Cryptomycota in the kingdom fungi. To do this it is important to understand the characteristics and life-cycle of Cryptomycota and what makes an organism part of the kingdom fungi. Characteristics of CryptomycotaThe known Cryptomycota :Rozella is a genus of entirely parasitic species that infect the thalli and sporidia of Chytridiomycota , Blastocladiomycota and some species of Oomycota. Study of Rozella allomycis , the only cultured Rozella species has shown it does ,unlike Fungi, not process cell walls at any time during there trophic phases like Fungi however they exhibit a zoosporic uniflagilate stage in which they propagate(Jones and Pang 2012) .
James and Berbee demonstrated that chitin is present in the inner cell wall of immature spores via calcofluor white staining(2012).Zoospores attach to receptors on the surface of its host ,penetrating its surface with a germ tube before developing a naked multinucleate sporangium (Jones and Pang 2012)It is theorised that the uptake of nutrients is via phagocytosis (Powell 1984), however this is not known to be true of all Rozella. Zoospores form inside the host before being explosive discharged from exit papillae(Jones and Pang 2012) . Jones et al’s observation of Cryptomycota cells show a certain similarity to the life-cycle of Rozella.Three life stage cycles were observed (fig 2), a zoosporic uniflagelate morph ,a non-flagellate cyst morph and a parasitic morph where the organism is attached to a host diatom . Jones et al admit, however, that stages in the life-cycle are likely to have been missed in their study and due to the diversity of the Cryptomycota, the life-cycle is unlikely to represent the entirety of the group (2011).
Chitin was not found in any of the stages observed (Jones et al 2011) FIG 2:Putative Cryptomycota skeleton life-cycle (Jones et al 2011)Are Cryptomycota fungi? The penguin dictionary of biology defines Fungi as a kingdom of eukaryotic primarilary acellular organisms typically organised into cylindrical hypha . Their nutrition is osmotrophic and never phagotrophic . Hyphal walls are characterised by chitin and ? -glucans (2004). Cryptomycota differs greatly from this standard definition of a fungi by not processing a cell wall ,forming hyphae and is likely to be phagotrophic. There are other organisms that are included in the kingdom fungi that do not fit with these definitions .For example yeasts reproduce by budding and are not organised into hypha.
Zoospores are a shared characteristic with zoosporic true fungi and in most phylogenies constructed Cryptomycota are basal to fungi. Information on the life cycle stages is incomplete , it is possible some examples of cryptomycota process a chitinous cell wall at some stage in their life-cycles (Jones et al 2011). As a lot is uncertain about the cryptomycota it is hard to include or exclude them from the kingdom fungi and it seems premature to dub them the most basal fungi .
As James and Berbee suggest the loss of a chitinous cell wall may be a secondary adaptation to parasitism not indication of a basal fungi (2012). Almost anything could be found and much needs to be before they can be defined as true fungi such as observation of cell division and determination whether members of cryptomycota are phagotrophic or not. What is certain that if this phylum is included in the kingdom fungi , the definition for the whole group must change.