CHYTRIDIOMYCOTA: CHARACTERISTICS, LIFE CYCLE AND HABITAT - BIOLOGY - 2024

Chytridiomycota or chytridiomyceta is one of the five groups or phylla of the Fungi kingdom (kingdom of fungi). So far, about a thousand species of Chytridiomycotas fungi are known, distributed in 127 genera.

The Fungi kingdom is made up of fungi; eukaryotic, immobile and heterotrophic organisms. They do not have chlorophyll or any other pigment capable of absorbing sunlight, therefore, they cannot photosynthesize. Its nutrition is effected by absorption of nutrients.

Figure 1. Aquatic fungus of the Chytridiomicota group, Allomyces sp. Its filaments or hyphae are observed. Source: TelosCricket

Fungi are very ubiquitous, they can live in all environments: aerial, aquatic and terrestrial. One of its most outstanding general characteristics is that its cell walls have chitin in their composition, which is not present in plants, but only in animals.

Fungi can have saprophytic, parasitic or symbiote life. As saprophytes they feed on dead matter and play a very important role as decomposers in ecosystems.

As parasites, fungi can settle inside or outside living organisms and feed on them, causing disease and even death. In the symbiotic life form they live associated with other organisms, reporting this relationship mutually beneficial among symbiotic organisms.

Fungal organisms can be unicellular or multicellular. The vast majority of fungi have a multicellular body with many filaments. Each fungal filament is called a hypha and the set of hyphae make up the mycelium.

The hyphae can present septa or septa. When they do not present these septa, they are called coenocytes; multinucleated cells, that is, they contain many nuclei.

Characteristics of the Chytridiomycota

The fungi belonging to the phyllum Chytridiomicota are the most primitive fungi from the point of view of biological evolution.

Habitat and nutrition

The Chytridiomycota are fungi whose habitat is mainly aquatic -fresh water-, although also in this group there are fungi of terrestrial habitat that inhabit the soil.

Most of these fungi are saprophytes, that is, they have the ability to decompose other dead organisms and can degrade the chitin, lignin, cellulose and keratin that compose them. The decomposition of dead organisms is a very important function in the recycling of necessary matter in ecosystems.

Some Chytridiomycotas fungi are parasites of algae and plants of economic importance for man, and can cause serious diseases and even death.

Examples of agricultural items with nutritional importance that are attacked by pathogenic Chytridiomycotas fungi are: corn (attacked by a complex of fungi that cause the “brown spot of corn”); potato (where the fungus Synchitrium endobioticum causes the disease "black potato wart") and alfalfa.

Other fungi of this phyllum live as anaerobic symbionts (lacking oxygen) in the stomachs of herbivorous animals. These fulfill the function of breaking down the cellulose of the grasses that these animals ingest, playing an important role in ruminant nutrition.

Ruminant herbivorous animals do not have the necessary enzymes to break down cellulose in the herbs they eat. By having a symbiotic association with Chytridiomycotas fungi that live in their digestive systems, they benefit from the capacity that the latter have to degrade cellulose to forms more assimilated by the animal.

Also in this group of Chytridiomycotas there are important lethal parasites of amphibians such as the fungus Batrachochytrium dendrobatidis, which causes the disease called chytridiomycosis. There are Chytridiomycotas parasites of insects and parasites of other fungi, called hyperparasites.

Figure 2. The world's amphibians are threatened with extinction by chitidriomycosis. Source: Pixabay.com

Among the Chytridiomycotas fungi parasites of insects are those of the genus Coelomyces, which parasitize the larvae of mosquitoes vectors of human diseases. For this reason, these fungi are considered useful organisms in the biological control of diseases transmitted by mosquitoes.

Zoospores and flagellate gametes

Chytridiomycota is the only group of fungi that produces cells with their own movement in some phases of their life cycle. They have flagellated spores called zoospores, which can move in water using the flagellum.

Zoospores are involved in the asexual reproduction of Chytridiomycota fungi. These fungi also produce flagellated gametes in their sexual reproduction. In both cases there is a single smooth flagellum.

The egg or zygote can transform into a spore or a sporangium, which contains several spores considered as structures of resistance to unfavorable environmental conditions. This ability to form spores or sporangia ensures the reproductive success of Chytridiomycota.

Cell walls

The cell walls of the fungi of the Chytridiomycota group are basically constituted by chitin, which is a carbohydrate of the polysaccharide type that gives them rigidity. Sometimes the cell walls of these fungi also contain cellulose.

Mycelium, rhizoids and rhizomycelia

The fungal body of Chytridiomycota fungi is coenocytic mycelial (composed of hyphae without septa or partitions) or unicellular. The hyphae are long and simple.

The fungi belonging to the Chytridiomycota group can form different vegetative apparatuses such as rhizoidal vesicles, rhizoids and rhizomycelia, whose functions are described below.

Rhizoidal vesicles have haustorium functions. Haustoria are specialized hyphae presented by parasitic fungi, whose function is to absorb nutrients from the cells of the host organism.

The rhizoids are short filaments that serve to fix the soil substrate and absorb nutrients. The rhizoids can form in a septum or septum, separated from the aerial hyphae (called sporangiophores).

Additionally, these fungi can also form a rhizomycelium, which is an extensive system of branched filaments or hyphae.

Lifecycle

To explain the life cycle of the fungi of the Chytridiomycota group, we will choose as an example the black mold that grows on bread, called Rhizopus stolonifer. The life cycle of this fungus begins with asexual reproduction, when a spore germinates on the bread and forms the filaments or hyphae.

Subsequently, there are hyphae that are grouped in superficial rhizoids in a similar way to the roots of plants. These rhizoids fulfill three functions; fixation to the substrate (bread), they secrete enzymes for external digestion (digestive function), and absorb organic substances dissolved in the exterior (absorption function).

There are other hyphae called sporangiophores, which grow aerially above the substrate and specialize in forming structures called sporangia at their ends. The sporangia contain the spores of the fungi.

When the sporangia mature, they turn black (hence the name black bread mold) and then split open. When the sporangia open, they release many spores, called anemophilic spores, as they disperse in the air.

These spores are carried by the action of the wind and can germinate forming a new mycelium or new group of hyphae.

When two different compatible or mating strains meet, sexual reproduction of the Rhizopus stolonifer fungus can occur. Specialized hyphae called progametangia are attracted by the production of gaseous chemical compounds (called pheromones), physically meet and fuse.

Then the gametangia are formed that also unite, merging. This fusion results in a cell with many nuclei, which forms a very hard, warty and pigmented cell wall. This cell develops by forming several zygotes or eggs.

After a latency period, the zygotes undergo cell division by meiosis and the cell that contains them germinates producing a new sporangium. This sporangium releases spores and the life cycle is restarted.

References

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