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Importance of Fungi part I

Though we usually think of fungi as organisms that cause diseases and rot food, fungi are important to human life on several levels. They are often detrimental and beneficial together.

Beneficial role of fungi

1. Decomposer: Nitrogen and carbon recycling in agriculture and forestation.

2. Used as food-

i. Edible mushrooms: Many gourmet and medicinal types of mushrooms are now commercially cultivated. Some examples are:

Fig. : Button mushroom (Agaricus bisporus)- Common in supermarkets all over the world. Source

Fig2: Oyster Shell mushroom(Pleurotus ostreatus). Another popular edible mushroom. Also known for its cholesterol-reducing effects. Source

Mushrooms and toadstools are not same, Although toadstools are identical twins to mushrooms, they have huge difference between them. Mushrooms are edible and nonpoisonous while toadstools are inedible and highly poisonous.

Fig: Poisonous Mushrooms; A) Amanita virosa (the ‘destroying angel’)-The pure white, but deadly. Source B) Amanita pantherina-panther cap. They contain such high levels of toxin that a single bite can be fatal to a debilitated individual. Source C) Conocybe filaris also contain amanitins. Source

ii. Nutrition: Mushrooms are a low-calorie food usually eaten cooked or raw and as garnish to a meal. Dietary mushrooms are a good source of B vitamins, such as riboflavin, niacin and pantothenic acid. The essential minerals-selenium, copper and potassium. Fat and Carbohydrate. Absence of vitamin C and sodium. In terms of the amount of crude protein, mushrooms rank below animal meats, but well above most other foods, including milk, which is an animal product. Furthermore, mushroom protein contains all the nine essential amino acids required by man.

Nutritional values per 100g of Mushrooms (Brown, Italian or Crimini, raw) are as follows [Source: USDA Nutrient Database]:

Energy 27Kcal
Carbohydrate 4.1g
Fat 0.1g
Protein 2.5g
Thiamine(B2) 0.1mg
Riboflavin(B2) 0.5mg
Niacin(B) 3.8mg
Pantothenic acid(B2) 1.5mg
Vitamin C 0 mg
Calcium 18mg
Phosphorus 120mg
Potassium 448mg
Sodium 0mg
Zinc 1.1mg

It contains natural ergosterols which produce vitamin D2 when exposed to ultraviolet light. A process now exploited for the functional food retail market.


3. Food processing Nowadays many fungal enzymes are being used in food processing industries and their impact is going to be felt much more in coming years.

i. Making Bread: The wonderful texture of bread is created by the yeast Saccharomyces cerevisiae, which ferments small amounts of sugars and liberates bubbles of carbon dioxide that become trapped in the dough and leave it.

C6H12O6 → 2C2H5OH ⇑ + 2CO2  

ii. Brewery industry: Different species of Saccharomyces such as S. cerevisiae, S. pastorianus, S. eubayanus are used to ferment barley and grapes and produce Beer and Wine.

iii. Blue Roquefort Cheese: The Blue Roquefort Cheese ripened by Penicillium roquefortii. When the curd is ready, breadcrumbs with Penicillium roquefortii growing on them are added, then the cheese is incubated until ripe.

Source

The fungi Penicillium roquefortii grows throughout the curd, assisted to some extent by holes punched in the substrate by the cheese maker. The colour of the blue-green veins that develop is due to the presence of innumerable conidia of the fungi.

iv. Soft-ripened Camembert cheese: Ripened by Penicillium camembertii. These moulds form a dense white mycelial mat on the outside of the cheese and giving the cheese a wonderfully smooth, soft, almost buttery consistency. The interior of a really ripe Camembert will have a rather viscous, almost fluid texture, and may ooze gently when cut.

Fig: Soft-ripened Camembert cheese. source

v. Brown colour of Chocolate: Chocolate is made from the beans of a small tree, Theobroma cacao. Cacao beans are fermented over a period of 5-6 days by a diverse array of apparently naturally occurring yeasts (29 species belonging to 11 genera have been isolated).

Source

The most frequently isolated taxa are Saccharomyces chevalieri, Pichia membranaefaciens, Candida krusei, Torulopsis holmii, and Torulopsis candida. During this fermentation the beans develop the brown colour we all recognize.


4. Industrial mycology : Primary and secondary metabolic products of fungi-antibiotics, organic acids, vitamins, enzymes and alkaloids. Industrial fermentation process for Penicillin production.

i. Antibiotics: In 1927, Sir Alexander Fleming was growing pure colonies of  Staphylococcus aureus (Gram positive) on plates of culture medium when one of the plates became contaminated by a mould.

Source.

A wide clear zone around the fungal colony showed Fleming that something was diffusing out from the mould and killing or inhibiting the bacteria. He isolated the mould and found that it was a species of Penicillium, P. notatum (now known as P. chrysogenum). So, Fleming named the unknown substance penicillin and brought it to the attention of other scientists.

In March of 1942, Anne Sheafe Miller Suffering from Streptococcus infection, Anne was lucky, the right patient in the right place at the right time. Though penicillin was discovered in 1929, it didn’t save life until 1942 (13 years later). After Pearl Harbour disaster in World War-II, the Rockefeller Foundation set up a collaboration among British and American scientists–biochemists, mycologists, pathologists–in Government research institutes, Universities, and Industry. Mass production of penicillin was started.

In 1945 Fleming, together with Florey and Chain, two scientists involved in the isolation and characterization of penicillin and its testing as a therapeutic agent, shared a Nobel Prize.

Colony of Penicillium chrysogenum source.

An important antifungal antibiotic, griseofulvin, was derived from Penicillium griseofulvum. It was described as early as 1936, but came into use only during the 1950s as an systemic fungicide used against plant pathogenic fungi, and taken orally in doses of up to a gram per day to combat recalcitrant dermatophyte infections (tineas). Swiss pharmaceutical company Sandoz routinely collect soil samples for microbiological analysis. In 1970 a soil sample collected in Norway yielded a culture of Tolypocladium inflatum (now called Tolypocladium niveum), which was found to produce a novel cyclopeptide with some interesting antifungal activity. Cyclosporine proved effective against rheumatoid arthritis, since the chronic inflammation in that condition was immune-mediated.  It is an effective immuno suppressant.

ii. Organic acids: Citric acid, which is used in foods and soft drinks, as well as in cosmetics and leather manufacture, is produced on an industrial scale by Aspergillus niger. It is a major industrial fungal fermentation product after ethanol. Fumaric acid, used in making wetting agents and alkyd resins, is produced by Rhizopus nigricans. Gibberellic acid, derived from Fusarium moniliforme, is a plant growth hormone.

iii. Vitamin: Riboflavin (vitamin B2), produced by Eremothecium ashbyi, is a vitamin supplement.

iv. Enzymes: Fungi secrete (that is, produce and release) a variety of enzymes into their surroundings in order to digest food or to dissolve their way through solid substrates. Fungal enzymes that have been industrially exploited are as follows:

  • Amylase brings about the hydrolysis of starch to dextrin and sugars, and is used in the preparation of adhesives and sizings, and to clarify fruit juices. Produced by Aspergillus niger, Aspergillus oryzae.
  • Invertase catalyses the hydrolysis of sucrose to glucose and fructose, and is used in candy-making and in the preparation of syrups that will not crystallize. Produced by Aspergillus flavus, Aspergillus caespitosus, Saccharomyces cerevisiae.
  • Peroxidase produced by the mushroom Coprinus can decolourize dyes that have migrated from dark to light clothes during laundry, but won’t work in hot soapy water.
  • Fortunately, directed molecular evolution (very neo-Darwinian) has produced a heat-resistant version of the enzyme. Pectinase is used to clarify fruit juices, and to accelerate the retting of flax (the liberation of the fibres from the stems) preparatory to the making of linen, produced from Aspergillus niger.
  • Cellulases hydrolyze cellulose to cellobiose, and are used in food processing. They are usually derived from Trichoderma.
  • The current craze (2005) for ‘stone-washed’ jeans is also made possible not by stones but by the activities of Trichoderma. (Trichoderma reesei and Trichoderma atroviride) The jeans are steeped in a vat containing Trichoderma: its cellulases partially digest the fibres of the material, producing the much-prized ‘stone-washed’ softness and appearance.
  • Alpha-galactosidase derived from Aspergillus niger, is the active ingredient of “Beano” a product designed to prevent flatulence when beans or brassicas are eaten. Many people simply can’t metabolize the galactose in these foods, which is then fermented by bacteria in the gut. Beano breaks down the galactose and so prevents the embarrassing accumulation of gas, inhibit fart (to break wind), Aspergillus oryzae.

5. Fungi in Agriculture:

Beneficial aspects-

i. Fungus in soil (members of Ascomycetous and Basidiomycetous fungi )

  • Decomposes organic matter
  • Decreases plant pathogen in soil
  • Improve soil structure.

ii. Mycorrhizae: (Myco= fungus; Rhizon= root). It is a mutualistic relationship between roots of vascular plants and fungi. Fungi help plants in uptake nutrients from soil and plant share its photosynthetic product with fungi.

Source

Plant benefits include:

  • Improved nutrient and water uptake
  • Improved root growth
  • Improved plant growth and yield
  • Improved disease resistance
  • Reduced transport shock
  • Reduced drought stress

Mycorrhizal fungi help in the mobilization of soil phosphorus and nitrogen into plants.

In many instances, establishment of new forest becomes difficult unless mycorrhizal fungi are artificially introduced into soil by inoculation.

Plant-growth-promoting-fungi (PGPF)

Some rhizosphere fungi develop mutually beneficial relationships. They are able to promote plant growth upon root colonization. They are functionally designated as ‘plant-growth-promoting-fungi’ (PGPF). PGPF are non-pathogenic, soil inhabiting saprophytes, have been reported to be beneficial to several crop plants not only by promoting their growth but also by protecting them from diseases.

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About Syeda Nusrat Jahan Mili

Syeda Nusrat Jahan Mili

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