Zoopagomycota

Zoopagomycota is the sister of Mucoromycota+ Dikarya. It comprises three subphyla: Zoopagomycotina, Kickxellomycotina, and Entomophthoromycotina.

    The primary ecologies of members of the phylum include pathogens and commensals of animals, parasites of other fungi and amoebae, and rarely, as plant associates. The phylogenetic placement of Zoopagomycota as sister to the remainder of non flagellated fungi is important for numerous reasons, but two are highlighted here. 

    First, diversification with animals and nonplant hosts occurred at least as early as diversification with terrestrial plants. This suggests that fungi were among the first terrestrial organisms and that fossils of the first land animals should be examined with greater scrutiny for fungal associations, potentially providing a more complete picture of early terrestrial fungi. 

    Second, the loss of the flagellum in fungi corresponds to other modifications, including the loss of the centriole. Most non flagellated fungi of Mucoromycota, Basidiomycota, and Ascomycota possess an organelle unique to fungi, the spindle pole body, which serves as the microtubule attachment necessary for chromosome segregation during nuclear division. 

    It has been hypothesized that the spindle pole body is derived from centrioles through the loss of the 9+2 microtubular system, though there is no support for this homology based on detectable sequence similarity. In contrast, Zoopagomycota lineages retain a functional centrosome that possesses a degenerate 9+2 microtubular system. 

    Furthermore, there is some evidence that the genus Olpidium, a zoosporic fungus that retains its flagellum and infects nematodes and plant roots of Brassicaceae, maybe a member of—or closely related to—Zoopagomycota. 

    Collectively, these observations suggest that Zoopagomycota is critical to understanding the evolution of fungi as they transitioned to terrestrial ecosystems. Zoopagomycotina contains a single order, Zoopagales. Species in this order include predators of nematodes (e.g., Stylopage) and nematode eggs (e.g., Rhopalomyces), predators of amoebae (e.g., Stylopage, Zoopage), and mycoparasites of mucoralean fungi (e.g., Syncephalis). 

    Hyphae are small in diameter, coenocytic, and they form haustoria on or within their hosts. Asexual reproduction is by conidia or sporangia according to species, and where known, sexual reproduction is by the production of zygospores. 

    Many of these fungi are obligate symbionts and thus are difficult to obtain in axenic culture, and for this reason, there is a paucity of molecular and genomic data. 

    Furthermore, these fungi are underrepresented in environmental sequence data, presumably due to the inadequacy of existing environmental sampling techniques (e.g., primer bias, insufficient reference data, etc.), and their internal transcribed spacer sequences are longer than most fungi, contributing to underrepresentation.

Kickxellomycotina comprises four orders: Asellariales, Dimargaritales, Harpellales, and Kickxellales. Species of Kickxellomycotina possesses hyphae that are regularly compartmentalized by bifurcate septa that are occluded by a lenticular plug. 

    Asellariales and Harpellales are associated with digestive tracts of aquatic stages of arthropods and comprise two of the four orders that have been treated previously as Trichomycetes; the other two orders, Amoebidiales and Eccrinales, are members of Mesomycetozoea, not the kingdom Fungi. 

    Asellariales has filamentous, branched thalli and reproduces asexually by disarticulation of the thalli into arthrospores. They occur in the digestive tracts of marine, aquatic, and terrestrial species of isopods andCollembola, where they are thought to function as commensals. 

    Harpellales have branched or unbranched filamentous thalli and they reproduce by trichospores, which are asexual spores with hair-like appendages. They attach to the hindgut of aquatic stages of arthropods via a holdfast and are generally considered to be in a commensal relationship with their host.

    Dimargaritales species are haustorial parasites of other fungi, with the best-known species occurring on mucoralean hosts, and Kickxellales includes mycoparasites and saprobes isolated from soil. Dimargaritalesand Kickxellales, as well as Zoopagales, produce unique sporangia called microsporangia. 

    These are cylindrical sporangia that arise from a bulbous structure, and one or more sporangiospores may occur in chains within the sporangium Entomophthoromycotina contains three classes, each with a single order: Basidiobolomycetes and Basidiobolales, Entomophthoromycetes and Entomophthorales, and Neozygitomycetes and Neozygitales. 

    These fungi are associated with animals as either commensal isolates from animal dung or as pathogens and parasites of insects. Many species are commonly isolated from soil and maintained in pure culture, which is consistent with a saprobic life cycle phase. 

    Basidiobolalesis commonly isolated from amphibian dung, although species are known to occur on the dung of many vertebrates. They produce primary conidia that forcibly eject a single spore which if it lands on an appropriate substrate will germinate to form a mycelium or otherwise will undergo repetitive germination, producing a secondary conidium. 

    Under some conditions nonforcibly discharged capilliconidia are produced from forcibly discharged conidia. These adhere to the outer surface of insects. Dispersal is then achieved when the insects are ingested by insectivorous animals, and after surviving gut passage, the fungus is excreted with the feces. 

    In a few cases, gut infections are known in various marine and terrestrial vertebrates, and human gut infections have been mistaken for Crohn’sdisease. The ecological function of Basidiobolales is speculative at this time because no definitive functional experiments have been performed, but its specificity to animal dung and placement in Zoopagomycota support interaction with animal hosts in the digestive system. 

    The phylogenetic placement of Basidiobolales with molecular- and genome-scale data is problematic. In all current data sets, it is characterized by long and unstable branches and its relationship to other Entomophthoromycotinais unambiguous at this time. 

    Entomophthorales, or literally, insect destroyers, comprise pathogens of insects. They infect their hosts via spores and multiply within the host as one- to two-celled hyphal bodies, which also can function as gametangia. 

    Upon the host’s death, the fungus ruptures through the cuticle segments, producing forcibly discharged primary conidia. Frequently, infected hosts alight in perched or elevated positions, a phenomenon is known as summit disease, which is thought to be an induced behavior or adaptation for spore dispersal of the pathogen. Neozygitales are pathogens of insects and mites. 

    They were classified as a family within Entomophthorales but were distinguished from Entomophthorales based on the shape and size of chromosomes, although inadequate molecular data currently exist to test this hypothesis. Neozygitesproduces adhesive capilliconidia similar to those of Basidiobolus