DEUTEROMYCETES: CHARACTERISTICS, LIFE CYCLE, NUTRITION - BIOLOGY - 2024

The Deuteromycetes, Deuteromycetes or deuteromycotas, also known as imperfect fungi are fungi that lack or are unaware of the sexual stage (hence the term "imperfect"). This taxon, which contained about 25,000 species, is currently not considered valid.

They are saprophytes in most cases, that is, they feed on decomposing organic matter. Some species can be parasitic on plants or animals, including man.

Deuteromycetes, Curvularia lunata, conidia. Taken and edited from micol.fcien.edu.uy/atlas/Deuteromycetes.htm

Some imperfect fungi are of commercial importance. Its main use is in industrial fermentation processes of food and beverages. They are also used for the production of medicines and biological control of pests.

characteristics

Deuteromycetes. Source: commons.wikimedia.org

Imperfect fungi have a great diversity of body shapes. Most of them are similar to the asexual phase of ascomycetes. Others can be confused with basidiomycetes or zygomycetes. Some species are unicellular.

The mycelium is formed by well-developed hyphae, inter or intracellular. The hyphae are highly branched, multinucleated, and have single-pored septa. The main component of its cell wall is chitin-glucan.

Reproduction is asexual, generally by means of non-flagellated spores called conidia. Conidia can be shaped like a sphere, cylinder, star, spiral, among others.

These spores are produced in structures called conidiophores. Conidiophores can be simple or branched. They can grow solitary or in groups forming spherical fructifications.

In some cases the fructifications are bottle-shaped, in those cases they are called pycnidia. If they acquire the shape of a saucer, they are called acérvulos.

Taxonomy

The traditional classification of fungi is based mainly on the characteristics of the fruit bodies and spores. These structures are produced during sexual reproduction.

Due to this, the fungi that did not present, or were unknown, this type of reproduction were included in the phylum deuteromycetes. Currently there are about 15,000 species of deuteromycetes grouped into 2,600 genera.

Many authors argue that deuteromycetes are really ascomycetes whose sexual phase is unknown, probably because it occurs very rarely. It is also possible that this phase was lost during the evolutionary process.

Several facts seem to support this theory: most deuteromycetes are very similar to the asexual (anamorphic) phase of ascomycetes; Most of the deuteromycetes to which their sexual phase (telomorphs) have been discovered, have been shown to be ascomycetes, the same results have been found in cross-reproductions in the laboratory and with molecular studies.

Many deuteromycetes that have been relocated to other taxa, had a known sexual phase and described as a different species. In those cases, they have kept both names, resulting in species with two scientific names.

The telomorph receives the name of the ascomycete “species” (or the corresponding group) and the anamorph the name it received as an imperfect fungus. However, the tendency is for only one name to be accepted.

Habitat

Deuteromycetes are ubiquitous organisms. Although most species are found in soils, some are indicated for aquatic environments and others even for air.

Some organisms live in a wide variety of environments, others are more restricted in their habitat. For example, some species grow only on decaying wood, others on litter, or on charred wood.

Some are specific parasites for a single host species, others can parasitize several different species.

Lifecycles

Deuteromycetes are also known as "asexual fungi" and "conidial fungi", since only the asexual phase is present in their life cycle. The rest of the fungi can reproduce both sexually and asexually, making their life cycles more complex.

The spores released to the environment are transported by the wind, the water, or some biological vector, and once they have settled in the appropriate substrate, they will germinate. Once the spore has germinated, the new fungus begins to grow and develop.

If the fungus grows on the substrate, it will reach maturity and reproduce in the place where it germinated. If it is an endoparasite, it must secrete enzymes that allow it to degrade the protective covering of its host.

Plant parasitic fungi secrete enzymes to degrade the cell wall. Those that parasitize insects, or entomopathogens, secrete chitinases. Dermatophytes, meanwhile, secrete keratinases.

Once sexual maturity is reached, they produce new spores in the conidiophores. In the case of endoparasites, when they mature, they project the conidiophores outside the host.

Once the spores are produced, they are released to the environment, from where they will be transported until they get where to germinate and start a new cycle.

Nutrition

Most deuteromycetes feed on decaying organic matter. Other species are parasitic on plants or animals.

Saprophytic species feed by means of enzymes that they release to the environment. These enzymes digest and solubilize organic matter, allowing it to be adsorbed by fungi.

Organic matter can be of plant origin, such as remains of leaves, trunks, charred plant remains, decomposing fruits. It can also be of animal origin: corpses, bones, antlers, feces, among others.

Parasitic species must produce and release substances that allow them to degrade the cell walls, exoskeletons or cuticles of their hosts in order to penetrate them and feed on their vital fluids or tissues.

Reproduction

Pithomyces conidiophores. Source: commons.wikimedia.org

Deuteromycetes reproduce asexually by spore formation, fragmentation, and / or budding of the mycelium. Sporulation is the most common form of asexual reproduction. The spores, or conidia, are asexual and aflagellate and are formed in the conidiophore by mitotic division.

Fragmentation consists of the spontaneous rupture of a hypha, producing pieces of hypha that separate from the fungus and are capable of developing and forming new organisms.

During budding, by cell division of the hypha, a bud is formed that will increase in size and develop, without separating from the fungus. When it has developed, it separates from its parent and forms a new independent organism.

As a mechanism to increase their genetic variability, on rare occasions, deuteromycetes may have a parasexual cycle. In this cycle, the exchange of genetic material occurs within the same organism.

During the parasexual cycle the following events occur: formation of a heterokaryotic mycelium, fusion of some pairs of haploid nuclei to form new diploid nuclei, mitosis of both types of nuclei, crossing between diploid nuclei during mitosis and haploidization of some diploid nuclei.

Haploidization is a process of mitotic division during which there is crossover and reduction in the number of chromosomes. With this process, haploid nuclei can be obtained from diploid nuclei without meiosis occurring.

Diseases

In plants

Many species in this group cause plant diseases. Corn, tomato and cotton rot, some forms of anthracnose, ulcers (cankers) and leaf burns, are some of the diseases attributed to deuteromycetes.

In animals

Some species of deuteromycetes are entomopathogenic that they can cause epizootics severe enough that they almost completely eliminate insect populations.

The fungus Metarhizium anisopliae attacks termites of the Heterotermes tenuis species, which in turn affect rubber (Hevea brasiliensis) in the Colombian Amazon.

Deuteromycetes of the genus Culicinomyces parasitize mosquitoes of the genus Anopheles. Other genera of fungi, such as Beauveria, Metarhizium, and Tolypocladium also attack mosquitoes.

The fungus Metarhizium anisopliae, from termite corpses. Taken and edited from

Dermatophyte fungi that affect animals are mainly deuteromycetes belonging to the genera Microsporum and Trichophyton.

A functional classification of dermatophytes separates them into zoophilic ones, which mainly affect animals but can be transmitted to humans; anthropophilic, found mainly in humans, rarely transmitted to animals; and geophiles, found mainly in the soil, associated with animal remains that contain keratin, infect both humans and animals.

In cattle, dermatophytoses are very frequent in countries with cold climates, due to the fact that the animals are kept in stables for long periods. Most lesions in healthy animals heal spontaneously within one to several months.

In humans

The main effect of deuteromycetes in humans is dermatophytosis. The Epidermophyton floccosum species is pathogenic for human beings, and is the main cause of "athlete's foot" and tinea cruris. Other dermatophytoses are the different types of ringworms (tonsurant, corporal, of the beard, facial, crural, foot, hand, inguinal).

Most dermatophytoses are not serious in healthy people, but they can be more serious in people with weakened immune systems.

In these cases, atypical and aggressive infections, extensive dermatitis and subcutaneous abscesses can occur. Another latent danger is that opportunistic bacteria can cause cellulitis on skin damaged by interdigital dermatophytosis.

Uses / applications

Some Deuteromycetes are used for industrial purposes, mainly for the fermentation of food and beverages. They are also used to obtain medicines, for example penicillin, obtained from the Penicillium fungus.

Deuteromycete, Cladosporium resine, a species that decomposes hydrocarbons. Taken and edited from

Some species are used for the biological control of insects (entomopathogens). These fungi have certain advantages over other microbial control agents, such as bacteria, protozoa, and viruses.

The imperfect / deuteromycete fungi and other fungi are capable of attacking all stages of insect development. They can also attack species of insects that are not normally susceptible to infection by bacteria and viruses.

References

1. M. Arabatsis, A. Velegraki (2013). Sexual reproduction cycle in the opportunistic human pathogen Aspergillus terreus. Mycology.
2. M. Blackwell, D. Hibbett, J. Taylor, J. Spatafora (2006). Research Coordination Networks: a phylogeny for kingdom Fungi (Deep Hypha). Mycology.
3. Fungi imperfecti. On Wikipedia. Retrieved on September 02, 2018 from en.wikipedia.org
4. M. Mora, A. Castilho, M. Fraga (2017). Classification and infection mechanism of entomopathogenic fungi. Archives of the Biological Institute.
5. JL Pitt, JW Taylor (2014). Aspergillus, its sexual states and the new international code of nomenclature. Mycology.
6. D. Sicard, PS Pennings, C. Grandclément, J. Acosta, O Kaltz, J. Shykoff (2007). Specialization and local adaptation of a fungal parasite on two host plant species as revealed by two fitness traits. Evolution.
7. J. Guarro, J. Gene, AM Stchigel (1999). Developments in Fungal Taxonomy. Clinical Microbiology Reviews.