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Fungi

Ancient history

In ancient history, the earth was graced with different organisms like bacteria and archaea (floating, thriving, and swimming) in the ancient ocean that covered almost all the earth. With time, this organism got larger and more complex. Once a time, dinosaurs ruled on the earth, followed by mammals. Nowadays, humans are the dominant species on earth who are ruling all over, but in history, we had hardly heard about the: age of the fungus!

Around 250 million years ago, 90% of life on the earth vanished (animals and plants were decimated). Massive fields of dead wood and dead animals started degrading, and an organism thrived on them. Yes, an organism named fungi that ate dead plants and animals resulted in the domination of the landscape. From there “golden age of fungi” had begun.

This organism is singularly called “fungus” and plural called “fungi”.

The study of fungi is called mycology.

Fungi

Fungi are multicellular eukaryotic organism that includes yeast, mushroom, and molds like microorganisms. These organisms are classified as heterotrophs (cannot make their food), and in the fungi kingdom, these organisms contain a cell wall and are omnipresent. Still, slime molds and oomycetes are exceptions that don’t belong to the fungi kingdom but are fungi.

These fungus organism are evenly distributed all over the earth and have great medical and environmental use. Various fungi-like organisms are included in the chromista kingdom. Fungi are distinguished in the plant kingdom and by animals due to their unique and physiological features (cell wall and cell membrane). Fungi can also be defined by their principal growth mode and nutrient intake.

Fungi are found in humans and other animals as skin infections or fungal diseases. Common examples of fungi are found in life – if we keep bread outside for some days, black or green spots appear on them. Mushroom and yeast are also common examples used to produce beer and bread. One common characteristic of these examples is that they survive and grow in moist and warm conditions.

Formation of fungi

• The formation of fungi starts from the tips of filament (hyphae) form where the whole body of the organism (mycelia) is made. Fungi digest organic matter externally before absorbing it into their mycelia.
• The structure of fungi includes four parts:- sporangium, spores, food source, and hyphae.
  

• The filamentous structure is found in almost all fungi except yeast cells.
• Hyphae – a long thread structure that forms a mesh-like structure called mycelium.
• The fungus cell wall comprises chitin and polysaccharides. This wall consists of the protoplast (differentiated in other cell parts such as cytoplasm, cell membrane, nuclei, and organelles).
• The cell nucleus is dense, clear, with chromatin threads and surrounded by a nuclear membrane.

Fungi Characteristics

Various characteristics of fungi are as follows:-

• Heterotopic: Fungi depend on others for their food, and food is stored in the form of starch.
• Fungi are non-motile, non-vascular, unicellular, multicellular eukaryotic organisms.
• They are seedless plant organisms (reproduce using spores).
• Due to the absence of chlorophyll, the organism does not perform the photosynthesis process.
• Reproduction mode can be sexual (happen due to the production of a pheromone chemical) or asexual.
• Fungi have very small nuclei surrounded by a nuclear membrane, and its envelope does not dissolve during mitosis.
• As compared to bacteria, fungi grow slower.
• Fungi develop from spores; therefore, there is no embryonic stage.
• Chitin biosynthesis occurs in fungi, and the cell membrane surrounds the cell.

Fungi classification

Fungi are studied under mycology as they can only be observed under the microscope. Fungi play an important role in shaping aquatic and terrestrial ecosystems as they can engage in organic matter degradation, formation of symbiotic relationships, and phosphate fixation. Based on research, fungi have been classified on the bases:-

1. Mode of nutrition
2. Mode of spore formation

This mode of division is further divided into many parts.

a) Based on mode of nutrition

This model has various types:-

1. Saprophytic

Examples of saprophytic fungi are- Penicillium, Rhizopus, and Aspergillus. Saprophytes cannot make their food. They feed on dead organic substances for nutrition. These are of two types:

• Ectophytic saprophytes ( grows on surface)
• Endophytic saprophytes (grows inside the body of organic matter)

2. Parasitic

Examples of parasitic are- Taphrina and Puccinia. They survive on other living organisms(host) for their nutrition. Firstly they attack the living or dead organisms and harm them by causing disease. The host and parasite relationship is called parasitism. Based on the location, these are of two types:-

• Ectoparasite ( survive on the surface of the host)
• Endoparasite ( survive inside the body of the host)

3. Symbiotic

Examples of symbiotics are lichens and mycorrhiza. They get nutrition and grow on other living organisms and mutually beneficial for both of them. Lichens are a great example as they show an association between algae and fungi. Algae provide food to the fungi, and in reverse, fungi provide shelter to them.

b) Based on the mode of spore formation

Fungi are differentiated on these points:-

1. Phycomycetes

In these types of fungi, mycelium is coenocytic and separate. Found in moist and marine places (decaying wood and aquatic habitats). For example, Mucor, Rhizopus, and Albugo.

2. Ascomycetes

Ascomycetes are widely known as sac fungi and are decomposers, coprophilous, parasitic, and saprophytic. Most of the Ascomycetes are multicellular, and rare are unicellular. Examples are Aspergillus, Claviceps, and Neurospora.

Sexual reproduction – Ascospores

Asexual reproduction – conidiospores

Mycelium – branch and separate form in Ascomycetes.

3. Basidiomycetes

Sex organs are absent, and mycelium is in separate and branched form. A common example of Basidiomycetes are mushrooms that grow in soil, tree trumps, and event logs. Other examples are:- Aspergillus, Neurospora, Agaricus, and Claviceps.

Sexual reproduction happens due to basidiospores.

Asexual reproduction happens with conidia, budding, or fragmentation.

4. Deuteromycetes

This type of fungi is imperfect fungi as they do not follow a regular reproduction cycle (only asexual reproduction).

Asexual reproduction happens by conidia (asexual spores)

We can see the vegetative phase of fungi in which mycelium is in a branched and separate form. Various examples are Alternaria, Colletotrichum, and Trichoderma.

5. Zygomycetes

The fusion of two different cells forms zygomycetes. Fusion can be sexual or asexual, in which hyphae are without septa.

Asexual fusion is called sporangiospores.

Sexual fusion is known as zygospores.

Reproduction: Yeast

Yeast cells are small that multiply themselves by budding process ( a daughter cell off from the parent cell). Yeast cells are the same size as red blood cells, but they are lemon-shaped single cells. A scar is left on the parent bud when a child bud breaks off. Bread and cheese formation is impossible without yeast (Saccharomyces). Yeast is used for the medical research of diseases like cancer and genetic research. Yeast in humans can cause infection due to a low immune system (candida).

Mushrooms

Every person knows about mushrooms as fungi as they are eatable or non- eatable. Mushroom has a large cap on the stalk that produces the spores released by mushrooms to produce and colonize new environments. Some mushrooms are poisonous (wild mushrooms mainly). They are found springing up on dead wood after cool, wet weather.

Reproduction in fungi can be vegetative, sexual, or asexual.

• Vegetative reproduction- This type of fungi reproduction happens through budding, fragmentation, and fission.
• Sexual reproduction- This type of reproduction takes place through oospores, Ascospores, and basidiospores.
  Sexual reproduction does not occur in all the cases of the fungi, as in some cases, a fusion of two haploid hyphae cannot form a diploid cell. Therefore an intermediate stage appears called a dikaryophase (stage followed by the formation of diploid cells).
• Asexual reproduction- This asexual reproduction occurs by conidia, zoospores, and sporangiospores.

Uses of fungi

Fungi play an important role in the biosphere and have great economic importance. It has lots of benefits and harmful effects too.

There are several uses of fungi such as:-

• Food – Fungi provide food to the humans like mushrooms cultured and act as edible food.
• Recycling– They survive on the dead and decayed matter to cycle it. Recycle organic matter and cover the economic losses of stored food.
• Medicines – Various fungi are used as antibiotics (to control human and animal diseases) like penicillin. It is a good source of vitamin C- citric acid.
• Processing food – Fungi like yeast is used for food fermentation (cheese and bread)
• Making alcohol – Without fungi, brewing alcoholic beverages are not possible.
  
• Bio-control agents – Fungi are used for exploiting insects and controlling pests. Spores of fungi are sprayed on crops.

Examples of fungi

Examples are – Yeast, moulds, mushrooms, and truffles.

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