MYCOLOGY

Different types of PHYLA

Phyla of fungi

- Oomycota
- Chytridiomycota
- Zygomycota
- Ascomycota
- Basidiomycota
- Deuteromycetes

Oomycota

"Oomycota" means "egg fungi". It refers to the large round oogonia, or structures containing the female gametes. Oomycetes are oogamous, producing large non-motile gametes called eggs, and smaller gametes called sperm.

They are filamentous protists which absorb their food from the surrounding water or soil, or may foray the body of another organism to feed. Oomycetes play an important role in the decomposition and recycling of decaying matter.

Oomycete can cause serious potato disease known as late blight or potato blight (picture shown below).

Chytridiomycota

Chytridiomycota is a division of the Fungi kingdom. The name refers to the chytridium (from the Greek chytridion, meaning "little pot"): the structure containing unreleased spores.

Chytrids
- the most primitive of the fungi and are mostly saprobic (degrading chitin and keratin).
- aquatic (mostly found in fresh water), although some are parasites of plants and insects. - They reproduce asexually and have spores that ‘swim’ through the water.

Life cycle of chytridiomycota

They caused diseases such as Chytridiomycosis and the Potato wart disease.

Chytridiomycosis

Chytridiomycosis is a highly infectious disease of amphibians, caused by the amphibian chytrid fungus Batrachochytrium dendrobatidis. Only the amphibian chytrid fungus is known to infect vertebrate species. Individual frogs are thought to contract the disease when their skin comes into contact with water that contains spores from infected animals.

The surface of the epithelium (outer layer of skin) of a frog with chytridiomycosis shows discharge tubes of spores of the fungus . Batrachochytrium dendrobatidis emerging from the surface.
Photo: Lee Berger and Alex Hyatt

Potato wart disease

Potato wart disease is a plant infection in particular, maize-attacking and alfalfa-attacking species caused by chytrids with Synchytrium endobioticum as an important potato pathogen

Potato Wart Disease, also called potato canker, is a fungal disease of potato sprouts, eyes and stolons.

Zygomycota

Zygomycota is a phylum of fungi which comes from zygosporangia, where resistant spherical spores are formed during sexual reproduction.

- They are arguably the most ecologically diverse group of fungi. Zygomycota are terrestrial organisms.
- Live close to plants, usually in soil and on decaying plant matter.
- Zygomycota are also pathogens for animals, amebas, plants, and other fungi.
- Found in acquatic ecosystems.
- Also have some practical use.
(For example, certain species are used in Asian food fermentations.)

Zygomycota life cycle

Zygomycetes are known to cause serious infections, articularly for diabetics and immunocompromised individuals. These infections can also occur as a result of major burns or other tramatic injury. One such disease is zygomycosis, a rare fungal disease that occurs in humans, and can even affect the fetus.

Periorbital fungal infection known as mucormycosis, or phycomycosis

It is often caused by common fungi which can be found in soil and decaying vegetation. Different type of causes will affect different way to the human, example, Pythium or similar fungi it may affect the gastrointestinal tract or the skin.

Ascomycota

Ascomycota, also known as sac fungi, is a recently discovered class. In fact, it was once classified within Deuromycota. Ascomycota is a sister group to basidomycota.

Picture displaying Morchella deliciosa

- Established during the coal age, over 300 million years ago.
- The bodies are eukaryotic cells surrounded by a wall consisting of chitin and beta glucans.
- Are heterotrophic, obtaining nutrients from both dead and living organisms.
- Capable of consuming almost any liquid, as long as there is water present in it.
- Are truffels and morels.
- Contains fake morels.
- Single-celled (yeasts), filamentous (hyphal) organisms, dimorphic.

Life cycle of Ascomycota

Basidiomycota

- Contains about 30,000 described species, which is 37% of the described species of true Fungi.
- Produce mushrooms.
- Also includes yeasts and asexual species.
- Found In virtually all terrestrial ecosystems, as well as freshwater and marine habitats.
- Have a huge impact on human affairs and ecosystem functioning.
- Obtain nutrition by decaying dead organic matter, including wood and leaf litter
- Play a significant role in the carbon cycle.
- Frequently attack the wood in buildings and other structures, which has negative economic consequences for humans.

SEM of the surface of a mushroom gill (Coprinus cinereus: Agaricomycotina) showing several basidia, some with four basidiospores attached.

Lifecycle

The life cycle is as follows :

- Spores germinate into uninucleate hyphae.
- Two different hyphal strands can fuse to form a dikaryotic hyphae.
- It insure that each new cell contains a nucleus of each type a clamp connection must be formed - ( see diagram beneath. )
- Dikaryotic tissue forms the basidiocarp. As they develop, basidia form on the gills, which makes up the cap.
- As the basidia form the 2 nuclei fuse to form a 2N nucleus and then goes meiosis to form the 1N spores which are dispersed to the wind.

Clamp connections

Clamp connections are hyphal outgrowths that form when cells in dikaryotic hyphae divide.

One of the nuclei divides in the main axis of the hypha, while the other divides into the clamp. Septa are formed across each of the mitotic spindles. The apex of the backward-growing monokaryotic clamp cell fuses with the subapical cell, reestablishing the dikaryotic condition. All fungi that produce clamp connections are members of the Basidiomycota, but not all Basidiomycota produce clamp connections. The regular formation of clamp connections must have developed early in basidiomycete evolution, because they are found in all the major clades of Basidiomycota.

Sexually reproducing Ascomycota also form dikaryons, although they are not as long-lived as those of Basidiomycota. Ascomycota produce clamp-like "croziers" at the bases of asci (cells in which meiosis occurs, homologous to basidia). Croziers may be homologous to clamp connections.

Deuteromycetes

Conidiophore of Aspergillus

They are fungi that do not have sexually produced spores as part of their life cycle. Hyphomycete is sometimes used as more or less a synonym. Special names such as imperfect fungi which depends on the taxonomical system one is using. Given our mammalian, diploid prejudices. While perfect fungi is fungi that reproduce by means of sexual spores.

The stage of the fungus that produces sexual spores is called the teleomorph (or perfect stage), and the other life stage is called the anamorph (or imperfect stage).

Characteristics

What are fungi?

A fungus is a eukaryotic organism with membrane-bound nuclei and organelles. It is also a member of the kingdom fungi. Fungi are heterotrophic, they have to feed on performed organic material, and thus they are complex and dependent on environment changes. However, they are independent of light and are able to grow in dark habitats.

They grow in any directions and are able to invade the interior of the substrate with absorptive filaments. Due to these reasons, they can exist in anywhere and everywhere.

Figure 1.1 displaying structure of fungal cell

They can be microscopic or macroscopic. They have cell walls which are mostly made of chitin and glucan, unlike the cell walls of plants which are made of cellulose. Most fungi store their food as glycogen, just like human beings.

Most fungi grow as tubular filaments, forming thread-like, cell-walled structure called hyphae which initially develop from a germ tube that emerges from a germinating spore (Figure 2.1). Hyphae will eventually branch out to form a network of interlocking hyphae called mycelium (Figure 2.2).

Figure 2.1 displaying formation of hyphae

Figure 2.2 displaying formation of mycelium

Fungi are usually not motile as most members of the kingdom lack flagella; the structures are completely absent in all stages of their life cycle. The only exception is the chytrids, which produce flagellated gametes.

Majority of the fungi are aerobic, this means that they respire in the presence of oxygen. However, a small percentage of them are able to survive in the presence and absence of oxygen and they are falcutative anaerobic or obligate anaerobic.

Reproduction of fungi

Figure 3.1 displaying life cycle of fungi

Fungi can reproduce sexually or asexually. Some are strictly asexual or sexual while some are sterile(no spores).

Sexual spores are formed by a process called meiosis(Figure 3.2). It is when nuclei move from one mycelium to another to form a heterokaryon, a process called plasmogamy. The fusion of two haploid nucleus into a diploid nuclei(zygote) and the transform of the zygote into four haploid spores where the genomes are replicated once and separated twice to form new mycelia. There is genetic variation in daughter cells.

Asexual spores are formed by a process called mitosis(Figure 3.3). It is the duplication of one cell into two identical halves; therefore there is no genetic variation.

Figure 3.2 displaying formation of sexual spores through meiosis

Figure 3.3 displaying formation of asexual spores through mitosis

They produce exoenzymes to digest their food externally and absorb the nutrient molecules by their mycelia into their cells. They are non-autotrophic as they do not contain chlorophyll.

Fungi

Saprophytes

( - phyte meaning 'plant')

An organism which obtains its nutrients from dead or decaying organic matter.

Without fungi, nutrients would remain forever locked up in dead plants and animals.

Parasites

A parasite is an organism that depends on another organism, known as a host, for food and shelter.

A parasite usually gains all the benefits of this relationship. In contrast, the host may suffer from various diseases, infections, and discomforts as a result of the parasitic attack. In some cases, however, the host may show no signs at all of infection by the parasite.

Types of Parasites

Protozoa

Most parasites are one cell protozoa and they can invade any single cell in our bodies. Protozoa reproduce and multiply by duplicating themselves like a bacteria or virus. As parasites of humans, this group of organisms has historically been the cause of more suffering and death than any other category of disease-causing organisms.

Intestinal protozoa occur throughout the world. They are especially common in areas where food and water sources are subject to contamination from animal and human waste. Typically, protozoa that infect their host through water or food do so while in an inactive state, called a cyst. A cyst consists of a protozoan encased in a protective outer membrane.

Other types of parasitic protozoa infect the blood or tissues of their hosts. These protozoa are typically transmitted through another organism, called a vector. A vector is an organism that carries a parasite from one host to another host.

Helminths
Helminths are wormlike organisms (e.g. Roundworms, Tapeworms and Flukes). Leeches are also helminths and are considered ectoparasitic, since they attach themselves to the outside skin of their hosts.

Roundworms

Roundworms(also known as Nematodes), common among humans living in tropical developing countries, are Ascaris lumbricoides. This roundworm can grow to a length of 35 centimeters (15 inches) within the small intestine of its host.

Tapeworms

Tapeworms(also known as Cestodes) are a class of worms characterized by their flat, segmented bodies. Most tapeworms are ½ inch long and are a grayish-white color, but there are some species that can grow to 33 feet long and can lay over 1 million eggs per day. The segments hold both male and female reproductive organs, allowing self-fertilization. Adult tapeworms typically reside in the intestinal tract of vertebrates, attaching themselves to the stomach lining with hooks or suckers on their head.

Flukes

Flukes(also known as Trematodes) are the hardest parasites to get rid of as they can stay in the human body for 10-20 years with each adult fluke living for one year. Adult flukes are typically flat, oval-shaped worms that have a layer of muscles just below the skin. These muscles allow the worm to expand and contract its shape and, thus, move its body. Flukes usually have an oral sucker, sometimes ringed with hooks. They use the sucker to attach themselves to the host's tissues.

Arthropods
Arthropods are organisms characterized by exterior skeletons and segmented bodies. Examples include the crustaceans, insects, and arachnids.

Mosquitoes

Mosquitoes are the most notorious carriers of disease and parasites. Female mosquitoes rely on warm-blooded hosts to serve as a blood meal to nourish their eggs. During the process of penetrating a host's skin with their long, sucking mouth parts, saliva from the mosquito is transferred into the bite area. Any viral, protozoan, or helminth infections carried in the biting mosquito can be transferred directly into the blood stream of its host. Among these diseases are malaria, yellow fever, filariasis, elephantiasis, and heartworm. Flies also harbor diseases that can be transmitted to humans and other mammals when they bite to obtain a blood meal for themselves.

Flea

Fleas and lice are two of the most common and irritating parasitic insects of humans and livestock. Lice commonly live among the hairs of their hosts, feeding on blood. Some species are carriers of typhus fever. Fleas usually infest birds and mammals, and can feed on humans when they are transferred from pets or livestock. Another prominent class of arthropods that contains parasitic species is the arachnids. Included in this group are spiders, scorpions, ticks, and mites.

Mites

Mites are very small arachnids that infest both plants and animals. One common type of mite is the chigger, which lives in grasses. As larvae, they may grab onto passing animals and attach themselves to the skin, often leading to irritating rashes or bite wounds.

Ticks

Ticks live their adult lives among grasses and short shrubs. They are typically larger than mites. The adult female tick attaches itself to an animal host for a blood meal. Tick bites themselves can be painful and irritating. They carry a number of diseases that affect humans.

Symbionts

•Fungi have a mutualisticallybeneficial relationship with other living organisms.

1)Mycorrhizae: associations of fungi with plant roots
2)Lichens: associations of fungi with algae or cyanobacteria
3)Fungus-Insect symbiosis
4) Rumen fungi