Chytridiomycota

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Chytridiomycota
Differential interference contrast image of a spizellomycete chytrid thallus consisting of a large sphere filled with amorphous, bubbly cytoplasm and a much smaller, empty sphere to the left of the large sphere.
Sporangium of a spizellomycete
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Fungi
Division: Chytridiomycota
Hibbett et al. (2007)
Classes/orders

Chytridiomycota are a division of

Fungi, informally known as chytrids. The name is derived from the Ancient Greek χυτρίδιον (khutrídion), meaning "little pot", describing the structure containing unreleased zoospores. Chytrids are one of the earliest diverging fungal lineages, and their membership in kingdom Fungi is demonstrated with chitin cell walls, a posterior whiplash flagellum, absorptive nutrition, use of glycogen as an energy storage compound, and synthesis of lysine by the α-amino adipic acid (AAA) pathway.[2][3]

Chytrids are

parasites.[4] There has been a significant increase in the research of chytrids since the discovery of Batrachochytrium dendrobatidis, the causal agent of chytridiomycosis.[5][6]

Classification

Species of Chytridiomycota have traditionally been delineated and classified based on development, morphology, substrate, and method of zoospore discharge.[7][4] However, single spore isolates (or isogenic lines) display a great amount of variation in many of these features; thus, these features cannot be used to reliably classify or identify a species.[7][4][8] Currently, taxonomy in Chytridiomycota is based on molecular data, zoospore ultrastructure and some aspects of thallus morphology and development.[7][8]

In an older and more restricted sense (not used here), the term "chytrids" referred just to those fungi in the class Chytridiomycetes. Here, the term "chytrid" refers to all members of Chytridiomycota.[2]

The chytrids have also been included among the

Protoctista,[7]
but are now regularly classed as fungi.

In older

The class

Hyaloraphidiomycetes with a single order.[15]

fungal
phyla:

Life cycle and body plan

Chytridiomycota are unusual among the Fungi in that they reproduce with zoospores.[4][18] For most members of Chytridiomycota, sexual reproduction is not known. Asexual reproduction occurs through the release of zoospores (presumably) derived through mitosis.[4]

Where it has been described, sexual reproduction of chytrids occurs via a variety of methods. It is generally accepted that the resulting zygote forms a resting spore, which functions as a means of surviving adverse conditions.

thalli produce tubes that fuse and allow the gametes to meet and fuse.[4] In the last group, rhizoids of compatible strains meet and fuse. Both nuclei migrate out of the zoosporangium and into the conjoined rhizoids where they fuse. The resulting zygote germinates into a resting spore.[2]

Sexual reproduction is common and well known among members of the Monoblepharidomycetes. Typically, these chytrids practice a version of oogamy: The male is motile and the female is stationary. This is the first occurrence of oogamy in kingdom Fungi.[3] Briefly, the monoblephs form oogonia, which give rise to eggs, and antheridia, which give rise to male gametes. Once fertilized, the zygote either becomes an encysted or motile oospore,[4] which ultimately becomes a resting spore that will later germinate and give rise to new zoosporangia.[3]

Upon release from the germinated resting spore, zoospores seek out a suitable substrate for growth using

coenocytic and usually form no true mycelium (having rhizoids
instead).

Chytrids have several different growth patterns. Some are holocarpic, which means they only produce a zoosporangium and zoospores. Others are eucarpic, meaning they produce other structures, such as rhizoids, in addition to the zoosporangium and zoospores. Some chytrids are monocentric, meaning a single zoospore gives rise to a single zoosporangium. Others are polycentric, meaning one zoospore gives rise to many zoosporangium connected by a rhizomycelium. Rhizoids do not have nuclei while a rhizomycelium can.[3]

Growth continues until a new batch of zoospores are ready for release. Chytrids have a diverse set of release mechanisms that can be grouped into the broad categories of operculate or inoperculate. Operculate discharge involves the complete or incomplete detachment of a lid-like structure, called an operculum, allowing the zoospores out of the sporangium. Inoperculate chytrids release their zoospores through pores, slits, or papillae.[4]

Habitats

Chytrids are aquatic fungi, though those that thrive in the capillary network around soil particles are typically considered terrestrial.[7][4] The zoospore is primarily a means of thoroughly exploring a small volume of water for a suitable substrate rather than a means of long-range dispersal.[19]

Chytrids have been isolated from a variety of aquatic habitats, including peats, bogs, rivers, ponds, springs, and ditches, and terrestrial habitats, such as acidic soils, alkaline soils, temperate forest soils, rainforest soils, Arctic and Antarctic soils.[7][4] This has led to the belief that many chytrid species are ubiquitous and cosmopolitan.[7][4] However, recent taxonomic work has demonstrated that this ubiquitous and cosmopolitan morphospecies hide cryptic diversity at the genetic and ultrastructural levels.[20][21] It was first thought aquatic chytrids (and other zoosporic fungi) were primarily active in fall, winter, and spring.[4] However, recent molecular inventories of lakes during the summer indicate that chytrids are an active, diverse part of the eukaryotic microbial community.[22]

One of the least expected terrestrial environments the chytrid thrive in are periglacial soils.[23] The population of the Chytridiomycota species are able to be supported even though there is a lack of plant life in these frozen regions due to the large amounts of water in periglacial soil and pollen blowing up from below the timberline.

Ecological functions

Chytrid parasites of marine diatoms. (A) Chytrid sporangia on Pleurosigma sp. The white arrow indicates the operculate discharge pore. (B) Rhizoids (white arrow) extending into diatom host. (C) Chlorophyll aggregates localized to infection sites (white arrows). (D) & (E) Single hosts bearing multiple zoosporangia at different stages of development. The white arrow in panel (E) highlights branching rhizoids. (F) Endobiotic chytrid-like sporangia within diatom frustule; bars = 10  μm .[24]
meltpond, infected with two chytrid-like [zoo-]sporangium fungal pathogens (in false-colour red).[25]

Batrachochytrium dendrobatidis

The chytrid

Kihansi Spray Toad population in its native habitat of Tanzania,[26] as well as the extinction of the golden toad in 1989. Chytridiomycosis has also been implicated in the presumed extinction of the Southern Gastric Brooding Frog,[27] last seen in the wild in 1981, and the Northern Gastric Brooding Frog, last recorded in the wild in March 1985.[28] The process leading to frog mortality is thought to be the loss of essential ions through pores made in the epidermal cells by the chytrid during its replication.[29]

Recent research has revealed that elevating salt levels slightly may be able to cure chytridiomycosis in some Australian frog species,[30] although further experimentation is needed.

Other parasites

Chytrids mainly infect algae and other eukaryotic and prokaryotic microbes. The infection can be so severe as to control primary production within the lake.[3][31] It has been suggested that parasitic chytrids have a large effect on lake and pond food webs.[32] Chytrids may also infect plant species; in particular, Synchytrium endobioticum is an important potato pathogen.[33]

Saprobes

Arguably, the most important ecological function chytrids perform is decomposition.[7] These ubiquitous and cosmopolitan organisms are responsible for decomposition of refractory materials, such as pollen, cellulose, chitin, and keratin.[7][4] There are also chytrids that live and grow on pollen by attaching threadlike structures, called rhizoids, onto the pollen grains.[34] This mostly occurs during asexual reproduction because the zoospores that become attached to the pollen continuously reproduce and form new chytrids that will attach to other pollen grains for nutrients. This colonization of pollen happens during the spring time when bodies of water accumulate pollen falling from trees and plants.[4]

  • Dead frog with chytridiomycosis (B. dendrobatidis) signs
    Dead frog with chytridiomycosis (B. dendrobatidis) signs

Fossil record

The earliest

ma.[37]

In fictional media

The novel

Islamic extremists in an attempt to destroy the world's oil supplies, thereby taking away the technological advantage of the United States.[38]

The webcomic Black Mudpuppy by Ethan Kocak features an arc with an evil, anthropomorphic chytrid developed as a Nazi experiment to infect Xolotl, a giant, talking black axolotl.[39]

References

  1. ^ Tedersoo, Leho; Sanchez-Ramırez, Santiago; Koljalg, Urmas; Bahram, Mohammad; Doring, Markus; Schigel, Dmitry; et al. (22 February 2018). "High-level classification of the Fungi and a tool for evolutionary ecological analyses". Fungal Diversity. 90 (1): 135–159. .
  2. ^ a b c Alexopoulos, C.J.; Mims, C.W.; Blackwell, M. (1996). Introductory Mycology (4th ed.). John Wiley & Sons.
  3. ^ a b c d e
    Kendrick, Bryce (2000). The Fifth Kingdom (3rd ed.). Newburyport, MA: Focus Publishing.
  4. ^ a b c d e f g h i j k l m n o
    Sparrow, F.K. (1960). Aquatic Phycomyete (2nd ed.). Ann Arbor, MI: The University of Michigan Press.
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    Barr, D.J.S. (1990). "Phylum Chytridiomycota". In Margulis; Corliss; Melkonian; Chapman (eds.). Handbook of Protoctista. Boston, MA: Jones & Barlett. pp. 454–466.
  8. ^ a b Blackwell, W.H.; Letcher, P.M.; Powell, M.J. (2006). "Thallus development and the systematics of Chytridiomycota: an additional developmental pattern represented by Podochytrium". Mycotaxon. 97: 91–109.
  9. ^ Ainsworth; Sparrow; Sussman, eds. (1973). The Fungi: An advanced treatise. Vol. IVB A – Taxonomic review with keys: Basidiomycetes and lower fungi. New York, NY: Academic Press.
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  19. ^ Carlile, M.J. (1986). "The zoospore and its problems". In Ayres, Peter G.; Boddy, Lynne (eds.). Water, Fungi, and Plants. Vol. 11. Cambridge University Press.
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  26. ^ Dean, Cornelia (1 February 2010). "Saving tiny toads without a home". The New York Times.
  27. ^ Rheobatrachus silus species. Environment (Report). Profile and threats database. Government of Australia.
  28. ^ Rheobatrachus eungellensis species. Environment (Report). Profile and threats database. Government of Australia.
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  30. ^ "A salty cure for a deadly frog disease". Australian Broadcasting Corporation. 5 February 2018.
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  33. ^ Hooker, W.J. (1981). Compendium of Potato Diseases. International Potato Center. pp. 36–7. .
  34. ^ "The Chytridiomycota". Mycology. nbm-mnb.ca. Natural History of Fungi. Retrieved 28 October 2013.
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  39. ^ "Black Mudpuppy". Chytrid crisis: Part 1. 17 October 2016. Retrieved 29 August 2017.

External links