Phycology

Phylum Ascomycota Overview

The Ascomycota sac fungi is monophyletic and comprises about 75% of the described fungi. It comprises the majority of fungi that mix...

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This article writter by MN Editors on April 07, 2022

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Phylum Ascomycota Overview
Phylum Ascomycota Overview

The Ascomycota sac fungi is monophyletic and comprises about 75% of the described fungi. It comprises the majority of fungi that mix together with algae to create lichens as well as the vast majority of fungi do not have morphological evidence for sexual reproduction. Among the Ascomycota are some famous fungi: Saccharomyces cerevisiae, the yeast of commerce and foundation of the baking and brewing industries (not to mention molecular developmental biology), Penicillium chrysogenum, producer of penicillin, Morchella esculentum, the edible morel, and Neurospora crassa, the “one-gene-one-enzyme” organism. 

There are some notorious Ascomycota that are not well-known, some of the most dangerous being Aspergillus flavus, which produces aflatoxin, a fungal contaminant that is found in grains and nuts that is a toxin as well as the most potent carcinogen in nature, Candida albicans, cause of diaper rash, thrush and vaginitis.

 There is also Cryphonectria parasitica that is responsible for the death of four billion chestnuts in the eastern part of the USA. Asexual Ascomycota includes Penicillium and Candida species were previously separated from the Deuteromycota because sexual traits were essential to determine Ascomycota classification. However, the comparability of the nucleic acid sequence and nonsexual phenotypic characteristics, allowed the incorporation of asexual fungi within the Ascomycota.

Morphology of Phylum Ascomycota

Regarding the morphology, certain species are unicellular while other species are more complicated. The yeast is an excellent illustration of unicellular Ascomycota.

In addition to other yeast-like fungi of the phylum, yeast is basic structural Ascomycota fungus that is able to exist with only single cells. The form of yeast is different dependent on the location in which they’re grown and the type of food available. Because of this, yeast cells can take on different shapes.

Some other characteristics of these cells are cells with a wall, a huge vacuole, a granular cytoplasm, an nucleus and a nucleolus. Although yeast is able to exist as a single cell but they also change into multicellular organisms through an event known as dimorphism.

In these cases yeast cells (Candida yeast) produce pseudo-hyphae as well as hyphae and appear to be more complex than a single yeast with a single celle. In this condition, the organisms have been identified as pathogenic.

However Certain species, such as Aleuria aurantia (also commonly referred to as Orange peel fungus) are excellent example of multicellular organisms. In this way, they are more complicated.

A large variety of multicellular Ascomycota like A. aurantia, have an apex-producing body as well as large spores. When comparedto each other, multicellular organisms can be observed to differ in appearance, color, and size, in addition to being found in various habitats.

Similar to Basiodiomycetes Some also exist in collaboration with algae or Cyanobacteria. Through this symbiotic partnership the algae or cyanobacteria benefit the fungi by synthesising carbon compounds, while the fungi house the organism.

This causes the development of lichens which form a symbiotic connection between cynabacteria/algae and fungi. Another common connections is seen in mycorrhizal species, where the fungi seek refuge within the plant roots.

Based on morphology Ascomycota is classified into mycelial and saccharomycetes. While saccharomycetes are mostly single celled organisms, which includes true yeasts as well as other unicellular organisms Mycelial ascomycetes are the ones that are more likely to produce fruit-like bodies.

Some other characteristics that belong to this group are Woronin organs, bodies that go through a dikaryotic phases throughout their lives and septal pores.

Habitats

As a phylum that is diverse with a wide range of species, it is found in a wide range of habitats. For instance, while certain yeast (Candida yeast) are found within inside the human body (human beings) in which they can cause disease and other conditions, the more complicated Ascomycota such as Aleuria aurantia are terrestrial , and are found on habitats that have warmth, moisture or decaying materials.

There are a variety of species of Ascomycota that are located in aquatic habitats are Decorospora Gaudefroyi Julella avicenniae as well as Massarina and others, while others such as mycorrhizal species are discovered living in the plant roots.

Ascomycota Fruiting Body

A fruit-like body can be found in mycelial ascomycetes.

Sometimes referred to as ascomata or ascocarps, they are intricate structures made up of various types of cells. The asci that forms the nucleus, is in this intricate structure.

There are four kinds of fruiting body types that comprise:

  • Cleitothecia
  • Perithecia
  • Apothecia
  • Pseudothecia

Although fruiting bodies are mostly produced by mycelial Ascomycetes it has been proven to be dependent on a range of external factors , including:

  • Nutrient availability
  • Temperature
  • pH
  • Aeration
  • Light

If the conditions are favorable and when the vegetative mycelium has reached the appropriate stage in their competence begin to differentiate and form fruiting bodies. These are crucial in the reproduction of sexually of a few Ascomycota species.

Asci

Ascus (plural asci) is the common characteristic of the Ascomycota species. The cells (asci) are found within the ascomata/fruiting body. They are essential in creating ascomycete sexual spores (ascospores) which are involved in the reproduction of sexual sperm among a few of the species .

Asci differ in size and shape, ranging from species to species and also release spores which differ in size and shape.

The nutrition of the phylum Ascomycota

Ascomycota is a vast, diverse and varied phylum. This means that it is composed of numerous types of species that are found in various habitats. The organisms get their nutrients through a variety of sources that range from decaying and dead matter to nutrients from compounds made by other organisms like cynabacteria, as evident in their symbiotic relationship.

Certain species such as Ascomycota entomopathogenic have evolved to be able to infect and harm their hosts. However, they change to saprophytism. They are able to thrive in various situations.

The research has also demonstrated that members of the Ascomycota phylum practice carnivorism using specific structures to catch their prey, which includes nematodes.

To capture and trap these prey, they use traps such as constricting rings as well as adhesive traps, such as stalked glue knobs and sessile glue knobs, among others. They can catch, kill and get their food in their food sources.

Reproduction/Life cycles of ascomycetes

Like the majority of fungi undergo sexual and asexual reproduction.

Asexual Reproduction

The asexual reproduction process is carried out via:

  1. Fission or budding is the hallmark of bacteria, and fungi. It is found only in “fission yeasts” only.
  2. Fragmentation is a common feature in all fungi
  3. Chlamydospores and
  4. Conidia.

The Ascomycota have been specialized in conidia production. It is believed that conidia have attained their peak within this group. There are a variety of conidia made in a variety of ways. Conidiophores are found on the outside of the hyphae, or within fruiting bodies known as pycnidium (pl. is pycnidia) or Acervulus (pl. = acervuli).

Conidiophores can be independent or aggregated in a variety of ways. When conidiophores fuse, it is known as synnema (pl. = synnemata). The less compact fusions are referred to as a coremium. Conidiophores may originate from a cushion-like the stroma (a massive hyphal mass). It is referred to as a sporodochium.

A pycnidium can be described as a globular or flask-shaped fruiting body with an ostiole on the top. The Acervulus is a disc-like shape typically found under the cuticle or epidermis the plant host. Conidia can be found in various sizes, shapes and colors. Sometimes, conidial masses provide distinctive colour of the fungus e.g. Green-mold Penicillium or black-mold Aspergillus.

Reproduction/Life cycles of ascomycetes
Reproduction/Life cycles of ascomycetes

Sexual Reproduction

Sexual reproduction is accomplished through several methods, such as. gametangial copulation gametangial contact, spermatization , or Somatogamy.

1. Gametangial Copulation

Somatic cells can serve as gamestangia (example yeast) that fuse to form a diploid unicellular cell that develops to form an ascus. There isn’t a dikaryophase i.e. there is all times, the cells are not diaryotic.

2. Gametangial Contact

The morphologically distinct antheridia and ascogonia (sing. means ascogonium or female sexual organ) are found in certain Ascomycota. Ascogonia are generally round and have hair-like outgrowths called trichogyne. At times, however, it may be circular and is not any hair-like trichogyne.

The antheridia are typically club-shaped. The male nuclei are able to pass through the ascogonium via a pore created on the ascogonial walls near the junction with the antheridium. In certain species, the antheridia although present, are inactive (non-functional) while the ascogonia forms asci parthenogenetically.

3. Spermatization

Spermatia are conidia-like, small male cells that are created by short spermatiophores similarly to the way conidia are made through conidiophores. The spermatia enter the trichogyne, attach to it and release contents into the trichogyne. Male nucleus moves towards the ascogonium which is where it joins with female nucleus in order to make the dikaryon (nuclear pair).

4. Somatogamy

Somatic hyphae from compatible strains meld while the male nucleus is absorbed into the ascogonium via perforations in the septal. In many cases, somatic cells that are not differentiated serve as the ascogonium.

Parasexual reproduction

It is a procedure in which genetic recombination occurs by nuclear fusion or crossing over of chromosomes in mitosis. Meiosis doesn’t occur in the first place, instead, haploidization is triggered by the gradual loss of chromosomes in mitotic divisions. The theory is that all the processes of cytology occur in a predictable sequence that Pontecorvo (1956) calls”the parasexual cycle. The key steps include

  1. Nuclear fusion occurs between genetically different haploid nuclei within a heterokaryon , resulting in diploid nuclei
  2. Multiplication in the nuclei from diploids to the original haploid nuclei
  3. the formation of diploid homokaryons
  4. Genetic recombination occurs through crossing-overs during mitosis can occur in certain diploloid nuclei and
  5. A haploidization process occurs in some diploid nuclei due to the progressive loss of the chromosomes (aneuploidy) in mitosis.

Development of Ascus

Male nuclei on reaching the ascogonium stage, form the dikaryons (pairs of nuclei) together with female nuclei. They do not fuse immediately in order to create diploid nuclei like it happens in Zygomycota. Therefore, the karyogamy process is delayed. A dikaryophase occurs between karyogamy and plasmogamy.

Protuberances of small size appear within the ascogonium (or the somatic cell, acting like a female cells) they grow and develop into ascogenous hypohae. Diaryons multiply via the conjugate (simultaneous) divisions, and the daughter nuclear pairs are absorbed into the ascogenous Hyphae.

Then septa are laid out in the ascogenous hyperhae. Every cell in the ascogenous hypha is dikaryotic , with the exception of the terminal cell that has one nucleus. The dikaryophase within Ascomycota is expressed by ascogenous hypohae. remaining hyphae are monokaryotic, and are involved in the creation of a thick , protective layer over the asci.

A dikaryotic cell belonging to the ascogenous hyphae grows and forms an elongated hook or crozier-like cells which is also known as a crook. The two nuclei split mitotically so that their spindles lay in a horizontal line and are parallel to one the other. There are two daughters nuclei. One for each spindle, are located on the angle of the hook. The other nucleus is located at the tip and the other is close to the septum’s base.

A pair of septa is laid out and form three separate cells, the uninucleate basal as well as apical cells and a binucleate penultimate. The penultimate cell functions as the ascus’s first cell. The apical and basal cells eventually fuse, and the nucleus of the basal cells moves into the apical cells via a pore that is formed near the contact point.

In this way, the apical cells transforms into a binucleate, repeating the previous events to form an ascus-like cell. This happens repeatedly and a number of penultimate cells form which result in asci.

The final, or initial cells of the ascus, expand into an elongated club-shaped structure. The two nucleithat were a dikaryotic pair until the time of plasmogamy, fusion to create an ediploid nucleus. So, plasmogamy as well as the karyogamy take place in different places ascogonium; plasmogamy, and karyogamy inside the cell that was formed by the ascus.

The nucleus of the diploid undergoes meiosis, which results in development of four distinct nuclei. Separation of mating types as well as other characters happens in the meiotic division. The four nuclei formed by the mitotic division, create eight nuclei.

Ascospores are arranged around these eight nuclei through the formation of free cells. A small amount of cytoplasm is accumulated around each nucleus before walls are laid. The cytoplasm that remains unutilized is referred to as epiplasm and is used to feed the ascospores in development.

The ascus has proven to be an invaluable aid to geneticists in their analysis of the segregation of meiosis-related characters. Meiotic materials are arranged in a sequential manner and are able to be removed to conduct genetic analysis. The character segregation, whether it happens during the first or second meiosis division, can be identified. The reason is because the second meiosis division occurs mitotically, changing the tetrad into eight nuclei. Ascospores have the same genetic makeup.

All in all there are six types of segregation that can be observed and two patterns in the event that segregation of alleles occurs during the initial meiosis division, and four patterns when segregation is observed during the second phase of meiosis. The proportion of the kinds 1 and 2 to other types is determined by the location of the allele on the chromosome relative the centromere.

Formation of Ascoma (=Ascocarp)

As the asci develop the surrounding hyphae monokaryotic create a thick protective coating surrounding the asci that is developing. The wall is made up of pseudoparenchymatous or prosenchymatous fungal tissue. The protective coat and asci are collectively known as the ascomata. There are three types of ascomata recognized, namely. (cleistothecium, perithecium, as well as thecium.

Cleistothecium that is typically large, is totally closed. The perithecium has an ostiolate structure, which means it has pores and is typically flask-shaped. The apothecium can be described as an open cup-shaped ascoma that has an exposed the hymenium (layer comprised of asci). Asci are typically long and club-shaped however, globose or Ovoid asci are also common. These asci, which can be stalked or sessile are placed in a layer known as Hymenium.

In the asci of the hymenium, are hair-like structures sterile and hairy known as paraphyses (sing paraphysis, sing) that aid in dispersal and liberation of ascospores. The ascus wall can be bitunicate or uniunicate and is a significant characteristic in the taxonomy of Ascomycota. The asci that are unitunicate have two thin walls that appear to be one wall.

The bitunicate asci has an outer wall that is rigid and an inner wall that is extensible. The inner wall, upon maturation emerges after the break from the wall on its outer side. The wall that is extensible includes an apical pore which the spores are forcefully released. In unitunicate asci the ascospores can be ejected different ways: through a slit, a pore or operculum (lid) or through the breaking the wall of the apical. In the majority of Ascomycota ascospores, they are released violently.

Once the ascospores have reached the right substratum, they sprout and create the monokaryotic mycelium.

Relationships of Ascomycota to other Fungi

Ascomycota is a sister-group that is related to Basidiomycota. This connection is further confirmed by the existence in both phylas that have cross-walls (septa) that separate the hypahe into segments and also pairs of nuclei that are not fused in these segments following mating, and prior to the nuclear fuse (dikaryons). Additional evidence supports this is the apparent resemblance between the structures which coordinate simultaneous mitosis the two nucli of dikaryosis (Ascomycota Croziers as well as Basidiomycota clamp connections).

Discussion of Phylogenetic Relationships

Sexual Ascomycota all contain asci. A comparison of the small subunit nuclear ribosomal RNA gene sequences shows the existence of a monophyletic Ascomycota but evidence for the base branch isn’t sufficient (Berbee and Taylor 1993; Bruns et al. 1992). Early diverging Ascomycota have been classified in the Archaeascomycetes however, it is not clear that the support of the Monophyly group isn’t very strong (Nishida and Sugiyama 1994). The position of Neolecta in the Archaeascomycetes group is a bit surprising due to it having an ascoma an element that is not found in other Archaeascomycetes , or any Hemiascomycetes (Landvik and colleagues. 1992). There is however no reason to believe that the Hemiascomycetes would not have experienced ascomata when hyphal growth was restricted in favor of yeasts. The Hemiascomycetes constitute an extremely well-supported monophyletic taxon like the Euascomycetes (Gargas and colleagues. 1995). Asexual fungi that share molecular or morphological traits that are sexually Ascomycota are classified under the Ascomycota which includes Candida albicans (Hemiascomycetes) and Pencillium Chrysogenum (Euascomycetes).

Through comparing the sequences of nucleic acids and the timeframe of Ascomycota evolution was estimated (Berbee and Taylor 1993). It is believed that the Archaeascomycetes, Hemiascomycetes and Euascomycetes all were established during the age of coal, just over 300 million years in the past. The fossils from these early Ascomycota are unlikely to be easy to identify as they likely did not have ascoma, and their spores were not distinct. Fungal-like fossils claiming as being more by 1.0 or 1.2 billion years could be fake. The first ascomycete fossils ascomata and spores have been questioned because the date of their deposition considerably predates the molecular estimates of the time of emergence. The bodies that produce fruit could be zygomycetous, while the spores could have been were buried in sediments from earlier times or the molecular calculations might be inaccurate.

Hierarchical Classification Of The Ascomycota

This system is a modification of Eriksson et al (2001) which has 3 subphyla and 14 classes.

Subphylum Taphrinomycotina = Class Archiascomycetes 

This is the one that Nishida as well as Sugiyama (1994) identified as the Archaeascomycetes group. I have increased the level to subphylum according to the classification system from Ericksson (2000) which states that they are sisters to the rest of the Ascomycota as well as to be the group that the other Ascomycetes were born. But, the classes that follow differ structurally and, as per Ericksson (2000) the latter, by their SSU sequences of rRNA. This is why the diverse nature of the four classes is a sign that they have been excluded from the established and natural classifications: Saccharomycotina and Pezizomycotina. Additionally, I am troubled by their apparent infancy. The taxa (except the fission yeasts) are parasites, and consequently, seem primitive due to reduction. The book clearly isn’t finished with the taxonomy for the Ascomycota.

CLASS NEOLECTOMYCETES

  • These are fungi which produce massive fruiting bodies (ascocarps with a maximum of 9cm tall).
  • The ascogenous hypothalamus does not contain Crosiers.
  • The asci is opened by the cut.
  • Ascospores develop into conidia resembling yeast.
  • The mycelia and the fruiting bodies are connected to the spruce root and could be parasitic.
  • ORDER NEOLECTIALES: Neolecta 

CLASS PNEUMOCYSTIDOMYCETES

  • They live as parasites within the alveoli of some vertebrates, and are of great medical importance.
  • They are yeasts that split by the process of fission (not growing).
  • They fuse and form asci from 8 ascospores that resemble bananas. 
  • ORDER PNEUMOCYSTIALES: Pneumocystis

CLASS SCHIZOSACCHAROMYCETES  = OCTOSPOROMYCES

  • These are the yeasts that fission.
  • They recombine to form asci composed of up to eight ascospores.
  • They exist as saprobes in juices of fruit.
  • ORDER SCHIZOSACCHARIALES: Schizosaccharomyces

CLASS TAPHRINOMYCETES

  • Biotrophic parasites on seeds and ferns can cause the formation of galls, curly leaves the deformity of fruits and witches Brooms.
  • Subcuticular or intercellular dikaryophase mycelium in parasitic phase, surrounded by terminal chlamydospores and ascogenous cells, which form an ascus that is the form of a hymenium like layer. Following the nuclear union and on to mitosis ascogenous cells typically divide , forming a basal stalk cell with an ascus at its apex. Ascospores can form within the ascus, so that it appears multispored. saprotrophic phase of budding monkaryotic cells that can be grown in yeast form.  
  • ORDER TAPHRINALES: Taphrina, Protomycetes.

SUBPHYLUM SACCHAROMYCOTINA = HEMIASCOMYCETES

  • These are the yeasts that are budding.
  • Vegetative phase, yeast-like, unicellular or filamentous.
  • one-walled unicellular, and not borne on ascogenous hyphae. 
  • They are created singly after karyogamy. No ascocarps.

CLASS SACCHAROMYCETES

  • ORDER SACCHAROMYCETALES = ENDOMYCETALES
  • Saccharomyces, Dipoascus.

SUBPHYLUM PEZIZOMYCOTINA

  • They make up the bulk of ascomycota. 
  • Mycelia are formed by the organisms that create ascocarps (ascus-bearing structures also known as the ascomata) with the hymenia. 
  • Some taxa are affected by lichenization (enter in a synergistic relation with algae, forming the lichens). 
  • Certain taxa are unable to undergo meiosis. And, even though they may join, they cannot create ascospores, or asci. 
  • They were once referred to as”the Fungi Imperfecti or Deuteromycota. This distinction is clearly artificial. However, such symbiotic entities as lichens will not readily fit into the natural world unless their fungal the symbiont (mycobiont) receives full preference. 

In order to be in line with the current taxonomic system for fungal taxonomic I have included fungi that are lichenized within this system and explain the lichens on a separate page. This subphylum is akin to that of Ericksson (2000) however, I’ve added an additional 9th category, Laboulbeiomycetes, a group that is not clear according to Ericksson’s system.

CLASS ARTHRONIOMYCETES 

  • This class is believed to be monophyletic.
  • The majority people are affected by lichenization, and create asci that have multiple walls, slits and double walls.
  • The asci grow into an elongated rostrum as they release spores.
  • The ascocarps have apothecia, which is naked Hymenium.  
  • ORDER ARTHRONIALES: Arthonia, Chrysothrix, Melaspilea, Roccella, Arthrophacopsis.

CLASS CHAETOTHYRIOMYCETES

  • This class is believed to be monophyletic.
  • Most species are saprobes of living plants dead wood, lichens, dead wood and lichens.
  • Certain are pathogens for humans.
  • The ascocarps are a small perithecia which contains paraphyces. 
  • ORDER CHAETOTHYRIALES: Chaetothyrium, Capronia, Adelococcus, Verrucaria.

CLASS DOTHIDIOMYCETES 

  • Typically, they are formed as bitunicate asci inside the perithecia (members of the family Patellariales create apothecia).
  • The asci are usually in association with the paraphyses like structures (pseudothecia).
  • These spores form septates.
  • The Chaetothyriomycetes and this class is akin to the Loculoascomycetes of earlier systems , and is commonly called “bitunicate ascomycetes”.
  • There are five orders that can be recognized by this method (after Ericksson, 2000).
  • Certain families are likely the possibility of being transferred into Chaetothyriomycetes when more molecular details are made available.

ORDER CAPNODIALES: 

Capnodaria, Capnodium, Achaetobotrys, Antennulariella, Coccodinium, Metacapnodium.

ORDER DOTHIDIALES:  

Asci oval, club-shaped or cylindrical, and arranged in small lobes, without pseudoparaphyses within pseudothecia The pseudothecia are separated or placed on or within the stroma. Ascospores are usually are not iseptate. Dothidea, [Mycosphaerella, Guignardia both incertae sedis].

ORDER HYSTERIALES:

On dead woody branches as well as unfinished wood with distinct , boat-shaped carbonaceous pseudothecia, opening with a the longitudinal slit, and appearing to be apothecium-like when wet. Hysterium.

ORDER MYRIANGIALES

Most subtropical or tropical, epiphytes, parasites, or hyperparasites that feed on fungi or insects on live leaves and stems asci globose scattered in ascocarp. Myrangium, Elsinoe.

ORDER PATELLARIALES

Asci in apothecia. Patellaria

ORDER PLEOSPORALES

The asci are long and cylindrical. They’re and separated by pseudoparaphyses, forming the form of large, uniloculate, typically solitary pseudothecia. Ascospores typically dictyosporous or phragmosporous, with pigmentation.

Venturia, Delitschia, Leptosphaeria, Lophiostoma, Melanomma, Montagnula, Phaeosphaeria, Phaeotrichum, Pleospora, Sporormia, Teichospora.

CLASS EUROTIOMYCETES

  • This class is believed to be monophyletic.
  • Two orders can be accepted.
  • The Elaphomycetaceae make up a monophyletic group that shares a common ancestor with Eurotiales and should not be considered as a distinct order but they should be considered into a distinct suborder within Eurotiales.
  • Asci are tiny they are evanescent, and produced in different stages within the ascocarp. They can differ from a loose weft of hyphae with asci, to a more organized structure with a distinct wall. The ascocarp is typically protected by an esothecium (but osteolate in certain) Conidia are common widely distributed and frequently linked to soils, seeds and even as parasites of animals. “The green and blue molds”.
  • Certain such as Aspergillus as well as Penicillium are forms-taxa. The sexual structure aren’t known.
  • The class is divided into two orders.

ORDER EUROTIALES

Eurotium, Eupenicillium.

ORDER ONYGENIALES

Gymnoascus, Eremascus, Onygena, Ascosphaera, Arthroderma

CLASS LECANOROMYCETES

  • This class contains most of the lichenized fungi.  
  • Most produce asci in apothecia with a naked hymenium.  
  • Asci usually thin-walled with a thicker wall at the distal end.  
  • Dehiscence is rostrate.  
  • This class  is used for most of the discolichens, but it is not strongly supported in phylogenetic analyses.  
  • This is a large and diverse class of 5 orders and 5 genera.

ORDER AGYRIALES

Agyrium, Lithographa, Anamylopsora, Elixia.

ORDER GYALECTALES

Coenogonium, Gyalecta.

ORDER LECANORALES

Acarospora, Hymenelia, Anzia, Arctomia, Anthroraphis, Biatorella, Calicium, Calycidium, Catillaria, Cetradonai, Cladonia, Coccocarpia, Collema, Crocynia, Dactylospora, Gypsoplaca, Haematomma, Arctopeltis, Lecanora, Lecidea, Loxospora, Megalaria, Macarea, Miltidea, Micoblastus, Ophioparma, Pachyascus, Pannaria, Parmelia, Physcia, Porpidia, Psora, Ramalinia, Rhizocarpon, Sphaerophorus, Stereocaulon, Lobaria, Nephroma, Peltigera, Placynthium, Fuscidea, Letrouitia, Teloschistes.

ORDER LICHINALES

Gloeoheppia, Heppia, Lichina, Peltula.

ORDER PERTUSARIALES

Megaspora, Pertusaria.

CLASS LEOTIOMYCETES

  • They have thin-walled asci that are inoperculate.  
  • The mildews are part of this class (as indicated by molecular studies).  
  • Most produce apothecia (the mildews produce reduced cleistothecia).

ORDER CYTTARIALES

Cyttaria.

ORDER ERISIPHALES

Biotrophic parasites; ascocarps with 1 to several oval-shaped to club-shaped explosive asci; ascospores unicellular, colorless; chains of conidia arising in basipetal succession from mother cell on superficial colorless mycelium; penetration of host by haustoria confined to epidermal cells. “Powdery mildews.”

Erysiphe, Microsphaera, Uncinula.

ORDER HELIOTIALES (HELOTIALES)

Asci inoperculate in distinct hymenium in apothecia of varying form; mostly saprotrophic but with a few plant pathogens.

Monilinia, Bulgaria, Dermea, Geoglossum, Hemiphacidium, Hyaloscypha, Leotia, Loramyces, Phacidium, Rustroemia, Sclerotinia, Vibrissea, Ascocorticium.

ORDER RHYTISMATALES

Ascodichaena, Cryptomyces, Cudonia, Rhytisma.

ORDER THELEBOLALES

Thelebolus.

CLASS ORBILIOMYCETES

  • This class contains dry rot fungi, as well as taxa that feed on other plants.  
  • When in the presence of nematodes, some will elaborate capture mechanisms with which they can significantly reduce the populations of soil nematodes.  
  • Arthrobotrys is the anamorph (asexual form) of small cup fungi, in the genus Orbilia.

ORDER ORBILIALES

Orbilia, Hyalorbilia

CLASS PEZIZOMYCETES

  • Thin-walled asci operculate in distinct hymenium.  
  • Most produce apothecia of varying shapes, large to minute; saprophytic on soils, dung, wood and plant debris.  
  • Others (truffels) produce subterranean (hypogeal)  ascocarps that are modified apothecia in which the acsi have become inoperculate.  
  • This large class has a single order (PEZIZALES)

ORDER PEZIZALES

Anthracobia, Ascolobus, Ascodesmis, Caloscypha, Carbomyces, Gyromitra, Glaziella, Helvella, Karstenella, Acervus, Pyronema, Sphaerosoma, Peziza, Morchella, Rhizinia, Sarcoscypha, Sarcosoma, Tuber.

CLASS SORDARIOMYCETES

  • These have unitunicate asci in perithecia.  
  • The asci open by a pore.
  • This assemblage is supported by SSU rRNA as a natural group.  
  • The 8 orders are distributed among 3 subclasses: Hypocreomycetidae, Xylariomycetidae, and Sordariomycetidae.  
  • This is a large and diverse class of nearly 800 genera.

ORDER HALOSPHAERIALES

Halosphaeria.

ORDER HYPOCREALES

Perithecial fungi that have unitunicate asci; perithecia typically with a well-developed and well-developed stroma, which generally light-colored. Asci are cylindrical and long, with a swollen apex. 8 ascospores that have filiform and hyaline and split easily and are primarily parasitic on insects, grasses as well as spiders along with other types of fungi.

Bionectria, Melanospora, Claviceps, Hypocrea,Nectria, Niesslia.

ORDER MICROASCALES

Chadefaudiella, Microascus.

ORDER BOLINIALES

Endoxyla, Catabotrys.

ORDER DIAPORTHALES

Melanoconis, Valsa.

ORDER OPHIOSTOMATALES

Kathistes, Ophiostoma.

ORDER SORDARIALES

Perithecia are ostiolate and have persistent, unicate asci they are usually found in a stroma , which can consist of the fungus and host tissue, or only fungus tissue ascocarps are typically black and musty.

Annulatascus, Batistia, Cephalotheca, Chaetomium, Chaetosphaeria, Coniochaeta, Helminthosphaeria, Lasiosphaeria, Nitschkia, Neurospora, Sordaria. 

ORDER XYLARIALES

Amphisphaerella, Clypeosphaerella, Diatrype, Graphostroma, Hyponectria, Xylaria.

CLASS LABOULBENIOMYCETES

  • Primarily obligate parasites of insect and beetles. They have distinctive non-mycelial and distinct pattern of growth.
  • The main structure of the fungus the receptacle is connected to the host via basal cellular holdfast. It is a single, basic haustorium that penetrates host; Receptacles differ in its size and complexity in a row of 3 cells, while in other rows there is a large number of cells arranged in layers.
  • Lateral filamentous appendages as well as one or more sessile or stalked perithecia grow on receptacles with asci that are usually four-spored ascospores are usually are colorless, elongated, and, more than a spindle, two-celled with a big basal cell each one surrounded by a colorless , thickened envelope towards the lower part ascus wall deliquescence prior release of spores. 

ORDER LABOULBENIALES

Laboulbenia.

Characteristics of Ascomycetes:

  • The majority of species are terrestrial, though the majority of them live in marine and fresh water. The majority of ascomycetes saprophytic. Some can be parasites for insects as well as other species, and certain species are responsible for the spread of harmful plants with diseases. Certain ascomycetes are known to thrive on the dung of animals and are commonly referred to as the coprophilous fungal species (Peziza).
  • The members vary in shape and form. The yeasts and a few other members (e.g. Taphrina) are unicellular however, the majority of other members in this group have well-developed, extensively septate, branched mycelium with multinucleate or uninucleate cells as well as perforated septa.
  • In cells that are unicellular cells, the wall of the cells is made up of mannans and glucans In septate forms, it is composed of chitin and glucans.
  • The process of reproduction is asexual and involves diverse types of non-motile-spores like oidia, conidia, and chlamydospores. In unicellular varieties, fission, budding and fragmentation are the most popular methods for propagation.
  • They can be heterothallic or homothallic. In certain heterothallic species, even though the male (antheridium) as well as female (ascogonium) sexual organs are developed on the thallus of the same species and are self-incompatible. These species have the male gametes of one mating type fertilizes ascogonium from another types of mating. This process is referred to as physiological heterothallism.
  • Sexual reproduction occurs through gamestangial co-operation (e.g. yeast) Gametangial contact (e.g., Aspergillus, Penicillium, Erysiphe), the somatogamy (e.g., Peziza, Morchella) or sexual spermatization (e.g., Polystigma).
  • The sexual spore, which is haploid, is known as the ascospore. It is created naturally by the formation of free cells following meiosis and karyogamy within an asciform or sac-like structure, referred to in the ascus. If the sexual spore of a fungus has the character of an ascospore then the species is classified as classified as an Ascomycete regardless of the other characteristics. This is the only characteristic that is what differentiates Ascomycetes from other fungi.
  • Ascomycota are in morphological diversity. It includes organisms ranging ranging from yeasts that are unicellular and complex cup fungi.
  • Ninety-eight percent of all lichens possess one of the Ascomycota which is the fungal component that makes up the lichen. 
  • There are 2000 genera that have been identified and 30000 kinds of Ascomycota.
  • The most commonality between these distinct groups is the existence of a reproductive structure referred to as the ascus. However, in some instances it plays an insignificant importance in the cycle of life.
  • A few of the pathogenic plants include rice blast, apple scab and the ergot fungus, black knot, as well as powdery mildews.
  • The yeasts are used to make alcohol-based drinks and breads. Penicillium, a mold, is used to produce penicillin, an antibiotic.
  • Nearly half of the species belonging to the phylum Ascomycota have symbiotic relationships with algae that result in lichens.
  • Other species, like morels (a extremely sought-after edible fungus) have important mycorrhizal ties with plants thus enhancing intake of nutrients and water, and sometimes protection against insects.
  • Most ascomycetes are parasitic or terrestrial. Some are adapted to freshwater or marine environments.
  • The cells of hyphae vary in composition of b-glucans and chitin, like Basidiomycota. But the fibers are placed in a glycoprotein matrix that contains galactose, a sugar, and mannose.
  • The mycelium of ascomycetes generally composed of septate hyphae. There isn’t always a predetermined number of nuclei within each one of these divisions.
  • The septal walls contain septal pores that provide the cytoplasmic continuity across all hyperhae. If the conditions are right the nuclei can also move between septal compartments by using these septal pores.
  • One distinctive characteristic of Ascomycota (but not within any of the ascomycetes) includes the existence of Woronin-containing bodies on both sides of the septa, which separate the hyphal segments, which regulate those septal pores. If a hypha adjacent to it is broken, the Woronin bodies block the pores to stop the loss of cytoplasm in the compartment that has been ruptured. Woronin bodies Woronin body is a spherical hexagonal and rectangular membrane bound structure that have crystallized protein matrix.
  • A variety of ascomycetes are commercial significance. Certain ascomycetes play an important role for example, like the yeasts that are used for baking, beer brewing and wine fermentation. They also include truffles and morels that are considered to be gourmet delights.
  • Many of them are responsible for tree diseases, including Dutch the elm disease as well as apple blight.
  • They demonstrate the heterokaryosis phenomenon, i.e. the nuclei of two distinct kinds are present within one mycelium.
  • The bodies that produce fruit are known in the term as ascomata (sing. ascoma, formerly known as ascocarp). The ascomata can be classified into four types : cleistothecium (cleistothecial ascoma) and the perithecium (perithecial ascoma) as well as thecium (apothecial ascoma) ascostroma (stromatic stroma) or pseudothecium.

Significance of Ascomycetes

  • Certain Ascomycetes cause devastating plant diseases like Dutch Elm Disease (Ceratocystis Ulmi) and Ergot of Rye (Claviceps purpurea) and the apple the scab (Venturia inaequalis), powdery mildews of different crops (Erysiphe, Phyllactinia, Uncinula etc. ) and many more.
  • The most fascinating Ascomycetes is the yeast, which are important in many ways since they play a role in the creation of a variety of items from the brewery and bakery industries. To comprehend their importance to the human condition, one should just smell and taste freshly baked bread or an alcohol beverage.
  • Claviceps purpurea can cause ergot-related disease. Ergot is a source of alkaloids, including LSD (lysergic acid diethylamide) which is the well-known euphoric drug that is commonly used.
  • Penicillium spp. is involved in the making penicillin, the drug that has become a wonder.
  • Numerous ascomycetous fungi can be found in the making of cheese. They are the Japanese and Chinese frequently use members of the group ‘Aspergillus Flavus-Oryzae for the production of food and also important industrial alcohol.
  • Neurospora genetics as laid out by Dodge is a novel method of haploid genetics as well as biochemical genetics. It was only possible since the fungus Neurospora provided a brand new method for studying heredity.
  • Ciclosporin, an immunosuppressor , is made of the fungus Tolypocladium niveum. It is employed for organ transplants and immune-mediated diseases.
  • Many organic acids and enzymes are created by ascomycetes e.g. citric acid and gluconic acids proteases, amylases, etc.
  • Claviceps purpurea (Ergot) is a medicine to stop bleeding during menstrual period and to increase the speed of labour.
  • Aspergillus is used in the preparation of soy sauce and also to make other Asian alcohol-based drinks
  • Morels, Truffles and lobster mushrooms are all fungal treats.
  • Neurospora, Saccharomyces, etc. are extensively employed to research genetics.

Plant disease interactions

Their most damaging tasks is to act as an agent of a variety of plant diseases. For example:

  • Dutch elm disease, which is caused by the closely identical species Ophiostoma Ulmi as well as Ophiostoma novo-ulmi is responsible for the death of a number of Elms in Europe in Europe and North America.
  • The original Asian Cryphonectria parasitica has been responsible for the attack on Sweet Chestnuts (Castanea inflora) and has almost completely eliminated the once widespread American Chestnut (Castanea dentata),
  • A disease that affects Maize (Zea mays), which is particularly common across North America, is brought on due to Cochliobolus heterostrophus.
  • Taphrina deformans is the cause of leaf curl in peaches.
  • Uncinula necator is the cause of powdery mildew disease, that is a threat to grapevines.
  • Monilinia species cause brown rot on stone fruits such as Peaches (Prunus persica) and sour cherries (Prunus ceranus).
  • The members of Ascomycota such as Stachybotrys Chartarum are the cause of fading in woolen textiles. This is a regular problem in tropical regions.
  • Brown, red and blue-green molds eat away at food items and cause them to spoil. like Penicillium italicum, which turns oranges into rotten.
  • Cereals that have been infected by Fusarium graminearum have mycotoxins such as deoxynivalenol (DON) that cause Fusarium ear blight , mucous membrane and skin lesions after being eaten by pigs.

Human disease interactions

  • Aspergillus fuigatus, the most frequent cause of fungal infections within the lung of immune-compromised patients that often result in death. The most frequently cited cause of Allergic asthma that is often seen in patients suffering from Cystic fibrosis, as well as Asthma.
  • Candida albicans is a yeast that targets the mucous membranesof the mouth, may cause an inflammation of the mouth or vagina known as thrush, or candidiasis. It is often blamed for “yeast allergic reactions”.
  • The fungi such as Epidermophyton cause skin inflammation, but are not a major risk for those with strong immune systems. However, if your immune system is damaged , they could be life-threatening. For example, Pneumocystis jirovecii is responsible for serious lung infections that are common in AIDS patients.
  • Ergot (Claviceps purpurea) is a real threat to human beings when it is attacked by wheat or rye. It produces highly poisonous alkaloids that can cause ergotism if eaten. The symptoms include hallucinations, stomach cramps along with a burning pain that can be felt in the muscles (“Saint Anthony’s fire”).
  • Aspergillus flavus thrives on peanuts, among other hosts, produces aflatoxin, which harms the liver . It is carcinogenic.
  • Histoplasma capsuleatum is the cause of histoplasmosis that affects immunocompromised patients.
  • Blastomyces dermatitidis is the triggering cause of blastomycosis. It is an insidious and frequently fatal fungal infection that is occasionally seen among animals and human beings in areas in which the fungus is prevalent.
  • Paracoccidioides brasiliensis and Paracoccidioides lutzii are the causal agents of paracoccidioidomycosis.
  • Coccidioides immitis, and Coccidioides Posadasii are responsible agent for Coccidioidomycosis (valley fever).
  • Talaromyces marneffei, formerly called Penicillium marneffei causes talaromycosis.

Beneficial effects for humans

On the other hand ascus fungi have provided essential benefits to mankind.

  • The most well-known case could be the case of the mold Penicillium chrysogenum (formerly Penicillium notatum) that, likely to fight off bacteria that are competing produce an antibiotic, which under the name penicillin, brought about revolution regarding the cure of bacterial infective illnesses in late 20th Century.
  • The importance of Tolypocladium niveum as an anti-inflammatory is not exaggerated. It produces Ciclosporin that can be administered in Organ transplantation to avoid rejection it is also prescribed to treat auto-immune disorders like MS, even though there is some uncertainty regarding the long-term adverse effects of the treatment.
  • Certain ascomycete fungi are able to change their appearance relatively easily using the process of genetic engineering. They are then able to produce useful proteins like insulin and human growth hormone or TPa that is utilized to break up blood clots.
  • Many species are popular model organisms in biology, such as Saccharomyces cerevisiae Schizosaccharomyces Pobe and Neurospora crassa. The genomes of many species of ascomycete fungi are fully sequenced.
  • Baker’s Yeast (Saccharomyces cerevisiae) is used in the production of bread, wine and beer and wine, in which process sugars like glucose and sucrose are fermented in order to create carbon dioxide and ethanol. Bakers make use of the yeast to increase carbon dioxide production. This causes it to raise and the ethanol to evaporate while cooking. Vintners typically use the yeast to produce ethanol as well as carbon dioxide released into the air as the fermentation proceeds. Traditional producers and brewers of sparkling wines use both methods, with a primary fermentation of alcohol and a second one to create carbon dioxide bubbles that give sparkling wines with a “sparkling” appearance for wine, and the desired foam that is characteristic of beer.
  • Enzymes from Penicillium camemberti have a role in the production of dairy products Camembert and Brie and Penicillium roqueforti perform similar things for Gorgonzola, Roquefort and Stilton.
  • Within Asia, Aspergillus oryzae is added to a pulp of soaked beans to create soy sauce. It is used to break down the starch from rice as well as other cereals into sugars that can be used for the fermentation process to East Asian alcoholic beverages such as sake and huangjiu.
  • Additionally, certain members of Ascomycota are excellent edibles: Morels (Morchella spp. ) as well as truffles (Tuber spp. ) and lobster mushrooms (Hypomyces lactifluorum) are among the most sought-after delicacies of fungal cuisine.

References

  • Berman, Jules J. (2012). Taxonomic Guide to Infectious Diseases || Ascomycota. , (), 199–208. doi:10.1016/b978-0-12-415895-5.00036-2 
  • Taylor, Thomas N. (2015). Fossil Fungi || Ascomycota. , (), 129–171. doi:10.1016/b978-0-12-387731-4.00008-6 
  • Webster, John; Weber, Roland (2007). Introduction to Fungi || Ascomycota (ascomycetes). , 10.1017/CBO9780511809026(8), 226–249. doi:10.1017/CBO9780511809026.011 
  • https://en.wikipedia.org/wiki/Ascomycota
  • https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/ascomycota
  • https://www2.hawaii.edu/~johnb/micro/m140/syllabus/week/eucaryotes/fungi/ascomycota.html
  • https://byjus.com/neet/ascomycetes/
  • https://www.sparknotes.com/biology/microorganisms/fungi/section2/
  • https://www.pnas.org/doi/10.1073/pnas.1120915109
  • https://www.adelaide.edu.au/mycology/fungal-descriptions-and-antifungal-susceptibility/ascomycota
  • https://ascomycete.org/Ascomycota
  • http://comenius.susqu.edu/biol/202/fungi/ascomycota/ascomycota.htm
  • https://www.biologydiscussion.com/fungi/ascomycetes-features-and-significance-fungi/54816
  • https://microbewiki.kenyon.edu/index.php/Ascomycota
  • https://www.cambridge.org/core/books/abs/introduction-to-fungi/ascomycota-ascomycetes/407F92405C41B4B690F83BCEB11AC895
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Microbiology Notes is an educational niche blog related to microbiology (bacteriology, virology, parasitology, mycology, immunology, molecular biology, biochemistry, etc.) and different branches of biology.

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