Applied Mycology

 

Role of Fungi in Biotechnology

Fungi are among the most important microorganisms used in biotechnology because of their rapid growth, ease of cultivation, ability to utilize inexpensive substrates, and capacity to produce a wide variety of commercially valuable metabolites and enzymes. They have extensive applications in the food, pharmaceutical, agricultural, and environmental sectors.

Major roles of fungi in biotechnology

• Food and fermentation industry: Fungi such as Saccharomyces cerevisiae are used in the production of bread, beer, wine, and other fermented foods. Species of Aspergillus and Penicillium are employed in the manufacture of soy sauce, cheese, and other fermented products.

• Production of industrial enzymes: Filamentous fungi secrete large quantities of extracellular enzymes such as amylases, cellulases, proteases, pectinases, and lipases. These enzymes are widely used in food processing, textile, paper, detergent, leather, and biofuel industries.

• Production of organic acids: Several fungi are commercially exploited for producing organic acids. For example, Aspergillus niger produces citric acid, while Aspergillus terreus produces itaconic acid, both of which have applications in the food, pharmaceutical, and chemical industries.

• Production of pharmaceuticals: Fungi synthesize numerous secondary metabolites of medicinal importance, including antibiotics (penicillin from Penicillium chrysogenum), immunosuppressants (cyclosporin A from Tolypocladium inflatum), cholesterol-lowering drugs (lovastatin from Aspergillus terreus), and antifungal agents.

• Agricultural applications: Mycorrhizal fungi improve nutrient uptake and plant growth, while species of Trichoderma, Beauveria, and Metarhizium are used as eco-friendly biological control agents against plant pathogens, insect pests, and nematodes.

• Environmental biotechnology: Fungi degrade complex organic pollutants such as lignin, dyes, pesticides, petroleum hydrocarbons, and plastics through extracellular enzymes, making them valuable agents for bioremediation and waste management.

Why fungi are preferred in biotechnology

• Rapid growth and easy large-scale cultivation.
• High secretion of extracellular enzymes simplifies downstream processing.
• Ability to grow on inexpensive agricultural and industrial wastes.
• Production of a diverse range of primary and secondary metabolites.
• Amenable to genetic improvement and metabolic engineering.

Applications of Fungi in the Food Industry

Fungi have been used in food production for thousands of years and are indispensable to modern food biotechnology. Their ability to ferment carbohydrates, produce enzymes, synthesize organic acids, and modify food flavour and texture has led to their widespread use in the manufacture of beverages, bakery products, dairy products, fermented foods, and protein-rich foods. Many fungi also serve as sources of food additives and processing aids.

1. Fermentation

Fermentation is a metabolic process in which fungi convert carbohydrates into alcohol, carbon dioxide, organic acids, or other metabolites under controlled conditions. It enhances the nutritional value, flavour, texture, digestibility, and shelf life of food.

In brewing or wine making industry alcohol is the important product. The other by-product which is carbon dioxide was formerly allowed to escape as a useless thing. Now carbon dioxide is also considered a valuable by-product. It is collected, solidified and sold as “dry ice”. In the baking or bread- making industry CO2 is the useful product. 

The yeasts secrete the enzyme complex called zymase which brings about conversion of sugar into alcohol. The yeasts lack diastase. So, they cannot break starch into sugar. 

A group of fungi, popularly known as the moulds, secrete a whole range of enzymes for fermentation of complex carbohydrates. 

In producing industrial alcohol, moulds are employed as starters to bring about scarification of the starch. At the second stage yeast is employed to act on the sugar.

The moulds commonly used for purpose of scarification are Mucor racemosus. M. rouxii and some species of Rhizopus. 

Other important fungal species include:

• Saccharomyces cerevisiae (baker's and brewer's yeast)
• Aspergillus oryzae
• Rhizopus oligosporus
• Monascus purpureus

Examples: 

Food product	Fungus used	Role
Beer	Saccharomyces cerevisiae	Alcohol fermentation
Wine	Saccharomyces cerevisiae	Ethanol production
Sake	Aspergillus oryzae; Saccharomyces cerevisiae	Starch saccharification and alcohol production
Soy sauce	Aspergillus oryzae	Enzyme production and flavour development
Miso	Aspergillus oryzae	Fermentation of soybean paste
Tempeh	Rhizopus oligosporus	Fermentation of soybeans
Red fermented rice	Monascus purpureus	Pigment and flavour production

2. Baking Industry

The baking industry primarily utilizes the yeast Saccharomyces cerevisiae, commonly known as baker's yeast.

Yeast ferments sugars present in the dough to produce:

• Carbon dioxide (CO₂)
• Ethanol

The carbon dioxide becomes trapped within the gluten network of the dough, causing it to rise. During baking, ethanol evaporates while the dough sets into a soft and porous structure.

Glucose → 2 Ethanol + 2 CO₂ + Energy

Applications

• Bread
• Pizza
• Cakes
• Buns
• Doughnuts

3. Flavour and Texture Development

Several fungi improve the flavour, aroma, colour, and texture of food through enzymatic degradation of proteins, fats, and carbohydrates.

(A) Cheese Ripening

Species of Penicillium are responsible for the characteristic flavour and texture of several cheeses.

These fungi secrete:

• Proteases that hydrolyse milk proteins.
• Lipases that break down milk fats.

These reactions generate amino acids, fatty acids, aldehydes, ketones, and esters that impart characteristic flavours and aromas.

Cheese	Fungus	Function
Roquefort	Penicillium roqueforti	Blue veins, strong flavour
Camembert	Penicillium camemberti	Soft texture and creamy flavour
Brie	Penicillium camemberti	Surface ripening

(B) Fermented Soy Products

Aspergillus oryzae produces:

• Amylases
• Proteases
• Lipases

These enzymes hydrolyse starch, proteins, and lipids, resulting in enhanced umami flavour and improved digestibility.

(C) Mushroom-Based Foods

Edible mushrooms include:

• Agaricus bisporus
• Pleurotus ostreatus
• Lentinula edodes

They are valued for their:

• Pleasant flavour
• Umami taste
• Meaty texture
• High nutritional value

4. Production of Organic Acids

Many fungi produce commercially important organic acids through aerobic fermentation.

Key Points

• Citric acid is the most commercially important fungal organic acid, accounting for the largest share of industrial organic acid production worldwide.
• Aspergillus niger is the workhorse fungus for the commercial production of citric acid and gluconic acid due to its high yield, rapid growth, and Generally Recognized as Safe (GRAS) status for many industrial applications.
• Most fungal organic acids are produced by submerged aerobic fermentation using inexpensive carbohydrate-rich substrates such as molasses or starch hydrolysates.
• Besides their role as food acidulants and preservatives, fungal organic acids are extensively used in the pharmaceutical, cosmetic, detergent, polymer, and chemical industries.

Organic acid	Major fungal producer	Substrate/ Raw material	Industrial production conditions	Major applications
Citric acid	Aspergillus niger	Molasses, sucrose, glucose	Aerobic fermentation; high sugar concentration; low pH (≈2); limited manganese ions	Acidulant and preservative in foods and beverages, pharmaceuticals, cosmetics, detergents
Gluconic acid	Aspergillus niger (A. foetidus also used)	Glucose	Aerobic fermentation with glucose oxidase activity	Food additive, pharmaceutical formulations, mineral supplements (calcium gluconate), cleaning agents
Itaconic acid	Aspergillus terreus	Glucose, molasses, starch hydrolysates	Aerobic submerged fermentation	Production of synthetic resins, biodegradable plastics, acrylic fibres, adhesives, and coatings
Fumaric acid	Rhizopus arrhizus (R. oryzae)	Glucose and other carbohydrates	Aerobic fermentation	Food acidulant, bakery products, beverages, confectionery, pharmaceutical formulations
Lactic acid	Rhizopus oryzae	Glucose, starch hydrolysates	Aerobic fermentation	Food preservative, biodegradable polylactic acid (PLA), cosmetics, pharmaceuticals
Malic acid	Aspergillus flavus, A. oryzae, Rhizopus spp.	Sugars	Fermentation under controlled pH and aeration	Food acidulant, beverages, confectionery, pharmaceuticals
Oxalic acid	Aspergillus niger	Sugars	Aerobic fermentation	Textile processing, metal cleaning, leather industry, chemical synthesis (limited food use due to toxicity)

5. Production of Industrial Enzymes

Fungi are preferred industrial producers because they naturally secrete extracellular enzymes, making enzyme recovery easier and more economical.

Enzyme	Major fungal source	Applications
Amylase	Aspergillus oryzae, A. niger	Hydrolyses starch into simple sugars. Used in bread making to improve dough quality and loaf volume, in brewing for starch conversion, in the production of glucose and maltose syrups, and in the manufacture of confectionery products.
Protease	Aspergillus oryzae, A. niger	Hydrolyses proteins into peptides and amino acids. Used in cheese manufacture, meat tenderization, baking to improve dough handling, production of protein hydrolysates, soy sauce fermentation, and clarification of beverages.
Lipase	Rhizopus spp., Aspergillus spp.	Hydrolyses fats and oils. Used for cheese ripening and flavour development, production of dairy products, synthesis of flavour esters, modification of edible oils, and processing of cocoa and chocolate products.
Cellulase	Trichoderma reesei, Aspergillus niger	Degrades cellulose into glucose. Used in fruit and vegetable processing, extraction of fruit juices, improvement of animal feed digestibility, coffee bean processing, and production of bioethanol from agricultural residues.
Pectinase	Aspergillus niger	Breaks down pectin in plant cell walls. Widely used for clarification and increased yield of fruit juices and wines, extraction of fruit pulps, improvement of fruit mash processing, and reduction of juice viscosity.
Xylanase	Trichoderma reesei, Aspergillus spp.	Degrades hemicellulose (xylan). Used in baking to improve dough elasticity and bread volume, enhance texture of baked products, improve cereal processing, and increase extraction efficiency of plant materials.
Invertase (β-fructofuranosidase)	Saccharomyces cerevisiae	Hydrolyses sucrose into glucose and fructose (invert sugar). Used in chocolate and confectionery industries to produce soft-centred candies, manufacture of invert sugar syrup, artificial honey production, and beverage processing.
Lactase (β-galactosidase)	Kluyveromyces lactis, Aspergillus oryzae	Hydrolyses lactose into glucose and galactose. Used in the production of lactose-free milk and dairy products, improvement of sweetness in dairy foods, prevention of lactose crystallization in ice cream and condensed milk, and manufacture of dairy ingredients for lactose-intolerant consumers.

Fungal enzymes are preferred in industrial food processing because they:

• Are secreted extracellularly, making their recovery and purification easier.
• Can be produced economically on inexpensive substrates through fermentation.
• Exhibit high catalytic efficiency under industrial conditions.
• Improve food quality, flavour, texture, digestibility, and shelf life.
• Reduce processing time, energy consumption, and production costs.
• Are generally recognized as safe (GRAS) when produced by approved fungal species such as Aspergillus oryzae and Saccharomyces cerevisiae.

Mycoproteins

Mycoprotein is a protein-rich food produced from the biomass of filamentous fungi grown by controlled fermentation. It is a sustainable, nutritious alternative to animal protein and is widely used in the preparation of meat substitutes.

Production

The most widely used fungus for commercial mycoprotein production is Fusarium venenatum.

1. Fusarium venenatum is grown under aerobic submerged fermentation in large fermenters.
2. The culture medium contains glucose or starch-derived carbohydrates, ammonia (as a nitrogen source), minerals, vitamins, and oxygen.
3. During fermentation, the fungus forms a network of protein-rich mycelial biomass.
4. The biomass is harvested and heat-treated to reduce its RNA content, preventing excessive uric acid accumulation upon consumption.
5. The treated biomass is mixed with suitable binders (e.g., egg albumin or plant-based binders) and processed into various food products.

Nutritional Value

Mycoprotein is considered a high-quality food because it contains:

• High protein content (approximately 40–50% dry weight)
• All essential amino acids
• High dietary fibre (mainly β-glucans and chitin)
• Low fat and low saturated fat
• Cholesterol-free
• Rich in vitamins (especially B-complex) and minerals

Applications

Mycoprotein is widely used in the manufacture of:

• Vegetarian and vegan meat substitutes
• Burgers
• Sausages
• Nuggets
• Minced meat alternatives
• Ready-to-eat meals
• High-protein functional foods

The best-known commercial product is Quorn™, marketed in many countries as a meat alternative.

Advantages

• Sustainable source of high-quality protein
• Requires less land and water than livestock farming
• Lower greenhouse gas emissions compared to meat production
• Rapid production through microbial fermentation
• High fibre content promotes satiety and digestive health
• Suitable for vegetarian and flexitarian diets

Limitations

• Some individuals may develop allergic reactions to fungal proteins.
• The biomass must be heat-treated to reduce RNA content before consumption.
• Production requires specialized fermentation facilities.

Feature	Description
Producer organism	Fusarium venenatum
Commercial product	Quorn™
Production method	Aerobic submerged fermentation
Protein content	40–50% (dry weight)
Major applications	Meat substitutes, burgers, sausages, nuggets, ready-to-eat foods
Major advantages	Sustainable, high protein, low fat, cholesterol-free

Secondary Metabolites of Fungi in Pharmaceutical Preparations

Secondary metabolites are low-molecular-weight organic compounds produced by fungi during the stationary phase of growth. Unlike primary metabolites, they are not directly involved in normal growth, development, or reproduction, but provide ecological advantages such as defense against competitors and environmental stress. Many fungal secondary metabolites possess potent biological activities and are widely used as pharmaceuticals.

Fungi produce a diverse range of bioactive compounds with antibacterial, antifungal, immunosuppressive, hypocholesterolemic, antitumor, and vasoactive properties. These compounds have revolutionized modern medicine and are extensively used in clinical practice.

1. Antibiotics

Antibiotics are secondary metabolites produced by microorganisms that, in low concentrations, inhibit the growth of or destroy other microorganisms without causing significant harm to the host when used therapeutically. Antibiotics are the most significant fungal secondary metabolites used to inhibit or kill pathogenic microorganisms.

Key Characteristics of Antibiotics

• Produced naturally by fungi or bacteria.
• Secondary metabolites synthesized mainly during the stationary phase.
• Active at very low concentrations.
• Possess selective toxicity against microorganisms.
• Widely used in medicine to treat infectious diseases.

Secondary metabolite	Producer fungus	Pharmaceutical application
Penicillin	Penicillium chrysogenum (formerly P. notatum)	Broad-spectrum antibiotic used to treat bacterial infections such as pneumonia, streptococcal infections, and syphilis.
Cephalosporins	Acremonium chrysogenum (formerly Cephalosporium acremonium)	β-lactam antibiotics effective against a wide range of Gram-positive and Gram-negative bacteria.
Griseofulvin	Penicillium griseofulvum	Antifungal drug used in the treatment of dermatophytic infections (ringworm, athlete's foot, tinea).

2. Immunosuppressants

The immune system recognizes transplanted organs (e.g., kidney, liver, heart) as foreign and attempts to destroy them, a process known as graft rejection. Immunosuppressant drugs inhibit specific immune responses, allowing the transplanted organ to function normally.

They are also used in autoimmune diseases, where the immune system mistakenly attacks the body's own tissues, such as in rheumatoid arthritis, psoriasis, and lupus.

Compound	Producer fungus	Application
Cyclosporin A	Tolypocladium inflatum	Prevents organ transplant rejection and treats autoimmune diseases
Mycophenolic acid	Penicillium brevicompactum	Used (as mycophenolate derivatives) in organ transplantation and autoimmune disorders by inhibiting lymphocyte proliferation

3. Cholesterol-Lowering Drugs (Statins)

Statins are not required for the normal growth or reproduction of the fungus. They are synthesized during the stationary phase of growth as secondary metabolites, likely providing ecological advantages by inhibiting the growth of competing microorganisms.

Statins act by competitively inhibiting HMG-CoA reductase (3-hydroxy-3-methylglutaryl coenzyme A reductase), the rate-limiting enzyme in the mevalonate pathway responsible for cholesterol biosynthesis in the liver.

Statins are widely prescribed for:

• Hypercholesterolemia (high blood cholesterol)
• Prevention of coronary artery disease
• Reduction of heart attack and stroke risk
• Management of atherosclerosis

Statin	Producer fungus	Remarks
Lovastatin (Monacolin K)	Aspergillus terreus	First naturally occurring statin used clinically
Compactin (Mevastatin)	Penicillium citrinum	First statin discovered; served as the prototype for later statins
Monacolin K	Monascus ruber/Monascus purpureus	Chemically identical to lovastatin; found in red yeast rice

4. Ergot Alkaloids

Ergot alkaloids are a class of nitrogen-containing (indole) alkaloids produced mainly by the fungus Claviceps purpurea, an obligate parasite of cereal crops such as rye, wheat, barley, and other grasses. They are synthesized in the fungal sclerotia (ergots) that replace the developing grains.

Although ergot alkaloids are mycotoxins at high doses, they have significant therapeutic value when administered in controlled amounts.

Secondary metabolite	Producer fungus	Application
Ergotamine	Claviceps purpurea	Treatment of migraine headaches and vascular disorders.
Ergometrine (Ergonovine)	Claviceps purpurea	Stimulates uterine contractions and is used to control postpartum haemorrhage.

Pharmaceutical significance

• Used in obstetrics to control excessive bleeding after delivery.
• Used in the treatment of migraine due to their vasoconstrictive action.
• Serve as starting materials for semisynthetic drugs, such as bromocriptine and cabergoline, which are used to treat:
  • Parkinson's disease
  • Hyperprolactinaemia
  • Acromegaly
• Have contributed significantly to the development of neuropharmacological drugs.

Toxicity

Consumption of grains contaminated with Claviceps purpurea sclerotia can cause ergotism, historically known as "St. Anthony's Fire."

Symptoms include:

• Severe vasoconstriction leading to reduced blood supply
• Burning pain in the limbs
• Gangrene
• Muscle spasms and convulsions
• Hallucinations and neurological disturbances
• In severe cases, death

5. Anticancer and Other Bioactive Metabolites

Several fungal metabolites exhibit anticancer, antiviral, antioxidant, or enzyme-inhibitory properties and are being explored for therapeutic applications.

Examples include:

• Fumagillin (Aspergillus fumigatus) – possesses antiparasitic and anti-angiogenic properties and has been investigated in cancer research.
• Cordycepin (Cordyceps militaris) – exhibits antitumor, antiviral, anti-inflammatory, and immunomodulatory activities.
• Mycophenolic acid (Penicillium brevicompactum) – used as an immunosuppressive drug in organ transplantation and autoimmune diseases.

Advantages of Fungal Secondary Metabolites

• Serve as a rich source of novel therapeutic compounds.
• Can be produced economically by large-scale fermentation.
• Many possess high potency and target specificity.
• Amenable to strain improvement and metabolic engineering for enhanced production.
• Continue to provide lead molecules for the development of new drugs.