Commonly called molds, Deuteromycetes are "second-class" fungi carrying no sexual state in their life cycle, reproduced only by producing spores via mitosis. This state of asexual fungi is called Anamorph. In other words, this imperfect fungi class falls under artificial fungi, of which there are approximately fifteen thousand species because of the asexual reproductive mechanism.
Deuteromycetes are also known as Deuteromycota, Deuteromycotina, fungi imperfecti, and mitosporic fungi.
The reproduction phase in Deuteromycetes takes place in different forms. Spores or Conidia is one such form produced directly on the mycelium or on the structure of specialized mycelial cells called Conidiophores. Some forms of these Deuteromycetes don't produce spores. Moreover, non-sporulating fungi are able to propagate themselves by fragmenting the hyphae or by producing a mass of hyphae called a sclerotium. Sclerotia can be microscopic in size or as large as several millimetres in diameter.
Deuteromycetes fungi carry some salient features that make them worth studying.
Deuteromycetes occur as saprophytes on a wide range of substrates, but a large number of these fungi are parasites on plants and animals. This causes a variety of diseases. Leaf- spots, blights, blotch, wilts, rots, anthracnose, etc. are the important diseases of plants, while diseases like meningitis, candidiasis, skin diseases, nail diseases, and others are caused in animals.
The mycelium is made up of profusely branched and septate hyphae posing multinucleate cells and simple pore septa.
The hyphae may be intracellular and their cell wall chiefly contains chitin-glucan.
Deuteromycetes reproduce only asexually. This method of asexual reproduction takes place by hyphal fragments, budding, arthrospores (flat-ended asexual spores formed by the breaking up of cells from the hypha), chlamydospores (thick-walled modified cells functioning as resting spores), and others.
The cell of conidiophores producing conidia is called a conidiogenous cell and is produced either at the tip or the side of the conidiogenous cell, either single or in chains.
The conidiophores are either free or aggregated to form specialized structures like Synnemata and Sporodochia. When they are large, the conidiophores are formed in specialized fruiting layers which are present within the specialized fruiting bodies called Conidiomata.
There is a low sexual reproduction, but the parasexual cycle generally operates in their life to fulfil sexual requirements.
There are thousands of Deuteromycetes species that are pathogenic to plants and plant parts. Many of these are responsible for the degradation of foods which include fruits and vegetables. All Deuteromycetes, like other types of fungi, are Heterotrophic and need to attach to an organic substrate. All major food products are the best substrates for fungi because, within a short period of time, the fungi will consume and destroy these fruits.
There are some fungi that are eligible to produce toxic chemicals harmful to those who like to eat rotting food. One such chemical is the aflatoxin, produced by the fungus Aspergillus flavus, and is majorly found on peanuts.
The Deuteromycetes is an artificial grouping in which the phylogenetic relationships among taxa are mostly unknown or not apparent. This classification comes under the mitotic states of meiotic groups such as basidiomycetes and especially the Ascomycetes. A small number of taxa has been correlated with meiotic states but the majority hasn't.
There are different formal and informal names used in the past for groups of mitotic fungi. The most common are Deuteromycotina, Deuteromycetes, Fungi Imperfecti, asexual fungi, conidial fungi, and anamorphic fungi.
The Deuteromycetes classification is characterized by the absence of teleomorphic (meiotic) states. It is heterogeneous, i.e., polyphyletic. Reproduction occurs commonly by spores (conidia) produced mitotically (asexually) from conidiogenous cells.
1. What are Deuteromycetes?
Molds are Deuteromycetes, which are "second-class" fungi with no known sexual state in their life cycle, and hence, reproduce only by creating spores through mitosis. The anamorph state is another name for this asexual state. The Deuteromycetes are not a class, despite the "-mycetes'' suffix; rather, this term is now used as a common name for this dumping-ground group of fungi. Approximately 90% of them have Ascomycota affinities. Members of this group are responsible for the majority of food deterioration and human fungal infections. As their "imperfect" absence of sex, they are also known as the fungus imperfecti.
When the "ideal state" of one of these organisms is identified, as it is every year, the fungus is more correctly categorised with the teleomorph name. However, it is difficult to remember to switch to their "married" name in practice, much as it is for people. It's worth noting that this group isn't categorised as a phylum. Although molecular biology techniques, such as PCR and DNA sequencing, can reliably assign most of these fungi into phyla, mycologists keep this group and its genera for convenience and tradition.
2. What are the problems faced during the taxonomic classification of Deuteromycetes?
Despite the fact that Fungi Deuteromycetes is no longer recognised as a taxon, many of the fungi it included are yet to be classified in the current fungal classification. This is because most fungi are classified based on the fruiting bodies and spores produced during sexual reproduction, yet Deuteromycota individuals have been reported to reproduce purely asexually or produce no spores.
Mycologists are the only people who research living creatures who use a dual naming system. Article 59 of the International Code of Botanical Nomenclature (which governs the name of plants and fungi) previously allowed dual naming; however, this was removed in the 2011 update of the Code.
A name for an asexually reproducing fungus was regarded as a form of taxon in the previous system. For example, Aspergillus niger, a common and industrially important mould, has no known sexual cycle. As a result, Aspergillus niger is classified as a form taxon. Isolates of its near relative, Aspergillus nidulans, on the other hand, revealed it to be the anamorphic stage of a teleomorph known as Emericella nidulans. When a teleomorphic stage is identified, it will take precedence over an anamorph's name. As a result, the previously classified Aspergillus species have been renamed Emericella nidulans.
3. What are the phylogeny and taxonomy of Deuteromycetes?
Molecular systematics is now widely used in the phylogenetic classification of asexually reproducing fungi. To infer links between asexually reproducing fungi and their sexually reproducing counterparts, phylogenetic trees created from comparative examinations of DNA sequences, such as rRNA, or multigene phylogenies might be utilised. Many asexually reproducing fungi have now been placed on the tree of life using these methods.
However, because phylogenetic methods require large amounts of biological materials from pure fungal cultures, the exact link between many asexual species and other fungal species has yet to be identified. Teleomorph names cannot be applied to fungi that lack sexual structures under the existing system of fungal taxonomy. The mycological community is still debating how to classify and name asexually reproducing mushrooms.
4. What are the biological aspects of Deuteromycetes?
As the fungi feed solely via absorption, rather than photosynthesis or ingestion, the growth of imperfect Deuteromycetes requires both cell wall-bound and external proteolytic enzymes to meet nutritional requirements. Extracellular proteinases released by fungal mycelia are known as aspergillopepsin. In an acidic environment, enzymes are extremely important for fungal feeding. At acidic pH, Aspergillopepsin I from Aspergillus saitoi exhibits two types of activity: pepsin-like catalytic function and trypsinogen-activating activity, similar to enteropeptidase.
Aspergillopepsin A, a 43-kDa protein whose activity is reduced by pepstatin, is the most important extracellular protease from Aspergillus niger, accounting for 80–85 percent of total activity. The aspergillopepsin A (pepA) gene is found on chromosome 1 of Aspergillus niger.
5. What is the description of genus?
Dark colonies, ranging in colour from grey to blackish-brown or black, characterise the Alternaria genus. Conidia are Dictyoptera dry conidia that can form simple or branched chains and have smooth or verrucose walls. They grow on conidiophores that normally develop and leave scars when separated. Conidia are generated through blastic ontogeny as protoplasm outgrowths through a specified apical pore in the conidiogenous cell, ranging in size from ovoid to subclavate and narrowing to the distal portion.
Some species develop a distinct beak. Alternaria may be mistaken with two additional taxa, Stemphylium and Ulocladium, which have similar spores. The former is defined by its persistent proliferation, whereas the latter is distinguished by its small base of conidia, which contrasts with Alternaria's large base.
6. Why are Deuteromycetes called imperfect fungi?
Imperfect fungi, also called Deuteromycota, are classified as fungi for two main reasons. First, their multicellular tissue is quite similar to the hyphae of sac fungi and club fungi. Secondly, they have erect hyphae with asexual spores called conidiophores, similar to sac fungi and club fungi.
Many imperfect fungi are related to the sac fungi because of their conidiophores closely resembling those produced by the sac fungi during their sexual phase. The imperfect fungi aren't placed in the Ascomycetes phylum because the classification of that group is completely based on the morphology of sexual structures.
Under the imperfect fungi, the best known is Penicillium. Some species falling under it appear as pathogenic and are found on vegetables and fruits.