ZYGOMYCOTA: CHARACTERISTICS, SYSTEMATICS, FEEDING, HABITAT - BIOLOGY - 2025

Zygomycota is a paraphyletic group that groups more than 1,300 species of fungi with different evolutionary origins. These have the common characteristic of producing zygospores, which are thick-walled, hard-walled zygotes, through which sexual reproduction occurs.

This group is an assemblage of six lineages whose relationships are yet to be defined: Mucoromycotina, Entomophthoromycotina, Mortierellomycotina, Zoopagomycotina, Glomeromycota and Kickxellomycotina.

Mature sporangiospora of Mucor sp. By Photo Credit: Content Providers: CDC / Dr. Lucille K. Georg, via Wikimedia Commons

Zygomycetes are the group of fungi with the greatest ecological diversity. They can be saprophytes in substrates such as fruit, soil and manure, symbionts in the viscera of arthropods, mutualists in plants that form mycorrhizae, and pathogens of animals, plants, insects, and other fungi.

In the food industry, various species are used in the fermentation of food. Rhizopus oligosporus is used in the preparation of Indonesia's staple tempeh, a fermented food derived from soybeans.

Rhizopus oryzae is used in the production of alcoholic beverages, in Asia and Africa. Actinomucor elegans is used in the preparation of tofu, a common soy-based food in oriental cuisine. They are also used as meat tenderizers, yellow coloring for margarine, among others.

On the other hand, some species have a negative economic impact. Rhizopus stolonifer and species of the genus Mucor cause rotting of fruits, particularly of strawberries.

Choanephora cucurbitarum is a plant pathogen that causes fruit and flower rot of various cucurbits. Species of the genus Mucorales cause life-threatening opportunistic infections in diabetic, immunosuppressed, and immunocompromised patients.

General characteristics

Mucoromycotina is the largest and best known clade. It includes about 300 species, common in all soils. They can infect plants and other fungi. They have been isolated in clinical samples. They are used in the fermentation of food.

The different lineages that make up the Zygomycota have different general characteristics.

Entomophthoromycotina is the second largest group of zygomycetes with approximately 300 species. It includes saprotrophic and entomopathogenic zygomycetes, soil and trash-associated. They can be saprotrophic, facultative pathogens, and mandatory entomopathogens. It is probably one of the first groups of terrestrial fungi.

Mortierellomycotina is home to over 100 taxa of saprotrophic soil organisms. All species in this subphylum are ubiquitous soil dwellers and saprotrophs, some of them are also plant symbionts.

Glomeromycota includes more than 250 described species that can grow only on the roots of host plants forming arbuscular mycorrhizae. There are ancient fossils of approximately 430 million years of morphology remarkably similar to that observed in modern fungi.

Kickxellomycotina and Zoopagomycotina include about 180 species in each subphylum. Many of these fungi are parasites of invertebrates, commensal arthropods, or saprotrophs. Some of them are important as insect pest pathogens.

Systematic

The system of fungi is in the process of reorganization. The traditional classification of fungi was based solely on morphological and physiological characteristics that do not necessarily reflect evolutionary history.

The modern classification of fungi is based primarily on groups defined by similarities in their rDNA sequences.

This new method has transformed traditional classification schemes. A 2017 study recognized eight fungal phyla, while a year later another study delineated nine sub-kingdoms and at least 18 phyla. Similarly, the relationships at the level of family, gender and species have not yet been resolved.

Thus, the interrelationships between species grouped in Zygomycota are currently under investigation. It is recognized that this is an artificial group, of paraphyletic origin, which does not currently constitute a valid taxon.

This group is an assemblage of the taxa Mucoromycotina, Entomophthoromycotina, Mortierellomycotina, Zoopagomycotina, Mucoromycotina, Glomeromycota and Kickxellomycotina.

Nutrition

Fungi are heterotrophic, they feed on nutrients that they absorb from the environment. Zygomicotes can be saprotrophic, parasitic or mutualistic symbionts, depending on their way of feeding.

Saprotrophic zygomycetes feed on waste from other organisms, such as dead plant matter (leaves, trunks, bark), carcasses, or excrement.

The fungi produce enzymes that are exuded into the surrounding environment and accelerate the decomposition of organic matter and the release of nutrients to the environment. A part of these nutrients are absorbed by fungi and another part is used by plants and other organisms.

Parasitic fungi absorb their food from the decomposition of the living tissue of their host, causing death in most cases.

Fungi that establish mutualistic symbiotic relationships feed on products excreted by their commensal without harming their survival.

The species of fungi that form mycorrhizae feed on a constant source of carbohydrates from the plant. While the plant benefits from the increased ability of the fungus to absorb water and nutrients, and mobilize minerals.

Habitat

Zygomycetes have been isolated primarily from the soil, where they rapidly colonize any source of easily degradable carbohydrates or proteins.

They can also be associated with garbage, animal manure or decomposing organic matter.

Parasitic species inhabit the viscera of insects and in the tissues of plants, animals and other fungi.

Other species can colonize hospital or nosocomial environments, becoming a serious public health problem.

Reproduction

The fungi of this group exhibit sexual and asexual reproduction.

The species of the order mucorales are the best known among the zygomycotts for their importance in the medical area. The fungi in this group reproduce sexually by thick-walled, hard-walled zygotes, known as zygospores. These are formed within a zygosporangium, after the fusion of specialized hyphae called gametangia.

Life cycle Mucor sp. By M. Piepenbring (M. Piepenbring), via Wikimedia Commons

Mature zygospores undergo a mandatory dormancy period before germination. However, in most species, the production of zygospores is rarer and the conditions necessary for their formation and germination remain unknown.

Asexual reproduction in mucorals occurs through a multisporation in which unicellular and non-motile sporangiospores are produced.

Mucorals produce not only dry air-dispersed sporangiospores, but also moist sporangiospores, less prone to aerosolization. This is an important characteristic that determines its level of pathogenicity.

Zygomycosis

More than 30 species of Zygomycota are involved in human infections. Among them Mucorales is the most abundant. Among fungal infections, zygomycoses are exceptionally serious, with a mortality rate greater than 50%.

The main route of access of zygomycete fungi to the body, in humans, is through the respiratory tract. The first barrier that spores meet are the hair cells of the respiratory epithelium. Those that do advance encounter alveolar macrophages that engulf and destroy most of the spores.

Other forms of infection occur through contamination of wounds or serious trauma, orally or by insect bites.

Patients at increased risk of infection

Most infections occur in newborns, who have not yet developed adequate immune mechanisms, or in immunocompromised hosts, transplant recipients, and diabetic patients with uncontrolled ketoacidosis and high serum iron levels.

In addition, patients receiving corticosteroids, deferoxamine in dialysis patients, immunosuppressive drugs, neutropenia, malnutrition, cytomegalovirus infection, and wounds or burns are also conditions that increase the susceptibility to developing zygomycosis.

Hospital or nosocomial infections can be due to contaminated medical devices, eg ostomy bag systems, adhesive bandage, wooden tongue depressors, subcutaneous insulin infusion pump, peritoneal dialysis, intravascular devices. T

It can also occur from contamination during medical procedures such as dental extractions, local anesthesia, intramuscular injection of corticosteroids, vitamins, and anticoagulants, nasal packing, graft contamination, and during transplantation.

There are five main clinical manifestations of zygomycosis: rhinocerebral, pulmonary, gastrointestinal, cutaneous, and disseminated:

Rhinocerebral zygomycosis

It is the most common form present in hematological and neutropenic diabetic patients. Initial symptoms are nonspecific, including headaches, altered mental status, fever, and eye syndrome, lacrimation, irritation, or periorbital anesthesia.

Unilateral vision disturbance and other changes involving ptosis, proptosis, or loss of extraocular muscle function are signs of infection progressing to the retroorbital region or central nervous system.

Pulmonary zygomycosis

Pulmonary zygomycosis usually occurs in patients with profound neutropenia, hematologic malignancies, being treated with corticosteroids, or in diabetics. Symptoms are non-specific and include fever, chest pain, and cough.

Gastrointestinal zygomycosis

It is a very rare form of infection. It is associated with severe malnutrition and premature delivery. The infection is believed to be a consequence of ingestion of fungi.

Symptoms are nonspecific and include fever, pain, vomiting, diarrhea, and constipation. The infection can lead to ischemic infarction and ulceration.

Cutaneous zygomycosis

The infection develops in patients who have suffered burns or other trauma. It is caused by direct inoculation during an accident or it can be nosocomial.

The manifestation of the disease involves erythema, pus, abscess formation, tissue inflammation, necrosis, and pain in the infected area.

Tissue necrosis can progress to gangrenous cellulitis. Skin infection may be secondary in patients with disseminated respiratory tract infection.

Disseminated zygomycosis

An infection is considered to be diminished when two or more non-contiguous organs are involved. This form is the most difficult to control and constitutes the greatest threat to the patient.

They often include lung and central nervous system colonization, with the lung being the primary site of infection. Other internal organs can be secondarily invaded during colonization, including the spleen, liver, and even the heart, causing pain in the infected organ.

References

1. James, Timothy Y. and Kerry O'Donnell. 2007. Zygomycota. Microscopic 'Pin' or 'Sugar' Molds. Version 13 July 2007 (under construction). Taken from tolweb.org
2. Muszewska, A. Pawłowska, J. and Krzyściak, P. (2014). Biology, systematics, and clinical manifestations of Zygomycota infections. European Journal of Clinical Microbiology & Infectious Diseases, 33 (8): 1273–1287.
3. Gryganskyi AP, Muszewska A (2014) Whole Genome Sequencing and the Zygomycota. Fungal Genom Biol 4: e116. doi: 10.4172 / 2165-8056.1000e116
4. Wikipedia contributors. (2018, August 3). Zygomycota. In Wikipedia, The Free Encyclopedia. Retrieved 04:27, October 14, 2018. Taken from en.wikipedia.org
5. Kavanagh, K. (2017). Fungi: Biology and Applications. Third Edition. Wiley Blackwell. Pp 408.
6. Royal Botanical Gardens (2018). State of the world´s fungy.