Role of Microbes in Industry


Alcoholic Fermentation

Ethyl alcohol is considered to be the oldest product of fungi. Many varieties of fungi bring about this alcohol through fermentation of sugar. Yeasts (Saccharomyces spp) are most commonly used in this connection. There are two species of Saccharomyces; one is the top fermenter (S. cervisiae) and the second is bottom fermenter (S. carlsbergonsis). Alcohol is usually produced by fermentation of molasses which is an aerobic process.

Micro-organisms utilize the carbohydrate present in molasses to obtain energy for growth and metabolic activities lead to the formation of alcohol. The reaction takes place via the Embden Mayerhof Paranas (EMP) pathway.

There are three main by-products of alcohol industry-carbon dioxide, higher alcohol (isoamyl) alcohol, butyl alcohol, collectively named as fuel oil) and alcohol. Alcohol is often used in manufacturing of ether, acetaldehyde, acetic acid, butanol, etc. Ethyl alcohol is one of the best known solvent of hundreds of different materials from which various compounds are synthesized. As a solvent, it is used in manufacture of such widely diverse materials as dye, soaps, plastics, polishes, synthetic rubber etc.

Butyl alcohol and acetone are also manufactured by the fermentation, which is brought about by the bacterial activity (Clostriditun acetobutylicum) on molasses. Both chemicals are of great industrial use.

Microbes in Organic Acid Production

A number of organic acids are produced by micro-organisms specially moulds and bacteria through the process of fermentation. These are as follows:

Citric acid: It is the most important product and is now produced commercially after fermentation by moulds like Aspergillus niger, Citromyces sp. and certain species of Mucor. Apart from these fungi, Pencilliium can also produce citric acid from sugar. The acid is used in manufacturing citrates, flavouring citrates, soft drinks etc.

Gluconic acid: Aspergillus niger synthesizes gluconic acid from sugar. Calcium, gluconate cures cow’s suffering from milk fever. It is also used in increasing calcium content of egg and in the preparation of toothpaste.

Gallic acid: Aspergillus gallomyces and Penicillim glaucum synthesize gallic acid.

Kojic acid: It is extracted from the mycelium of Aspergillus oryzae.

Acetic acid: Bacteria like Mycoderma aceti synthesize acetic acid from the fermentation of sugary solution and is used in vinegar production like Acetobacter aceti. A. xylinim and A. rances.

Microbes in Enzyme Production

Various micro-organisms like bacteria, fungi and protozoa produce different kinds of enzymes. They produce extracellular enzymes to break those organic and inorganic compounds, which have higher molecular weights. Simpler substances can easily be assimilated through cell membranes of micro-organisms.

Bacillus mesentericus is used for commercial production of amylase and protease. Bacillus macerans and B. polymyxa are also used for amylase production. Bacterial protease is employed to desize cotton and degum silk.

Fungi (Aspergillus oryzae) also synthesize amylase. Amylase is a starch digesting enzyme and is generally used in conversion of starch to fermentable sugars in alcohol industries. The commercial scale production of amylase is carried out by yeasts. Yeasts (Saccharomyces cervisiae) also produces an important enzyme called invertase which is used in production of confections. Ii brings about a partial hydrolysis of sugar into glucose and fructose. Apart from these important enzymes fungi, such as Penicillium glaucum and Aspergillus niger also produce enzyme-like pectinase and cellulose oxidase respectively.

Microbes in Fat Production

Micro-organisms, specially fungi synthesize fats. The most common fungi of this kind are: Aspergillus nidulans, A. sydowi, A. fisheri, Penicillium piscarum, P. javinicus. Endomyces vernatis etc.

Microbes in Retting of Fibres

Retting is the process in which plant fibres (jute, hemp, flax) are separated by the activity of micro-organisms. Plants are immersed in water for a considerable period. During the period, they absorb water and swell. The water medium becomes rich in harbouring bacteria (Clostridium butyricum) which hydrolyze the pectic substance of the middle lamella of fibre tissues. Consequently, the fibres get separated and are then used in preparing ropes, sacks etc.

Curing of Tobacco and Tea

Flavour and taste of tobacco and tea leaves are due to the fermentation of these leaves which is brought about by certain bacteria like Micrococcous candisans by the process referred as curing.


Milk and Curd

Milk is a complete food but it can also transmit diseases. It is an excellent nutritive medium for the growth of certain micro-organisms like bacteria, yeasts and moulds. These microbes alter the physical and chemical properties of milk. The common souring and curding of milk is brought about by the activity of bacteria (Streptococcus lactis) which is to convert lactose milk sugar into lactic acid by the action of enzyme produced by them.

The production of lactic acid gives milk a sour taste and in turn causes the precipitation of casein. These bacteria can be eliminated by healing the milk at 140°F continuously for 30 minutes. This heating process is called holding process. Flash pasteurization is an another method which involves heating of milk at 160-165 °F for 15 seconds and rapid cooling. This method also does not permit the growth of bacteria. The whole technique is referred to as pasteurization. This process does not affect the digestibility of milk.

Pasteurization has two advantages: (a) reduction in the spread of pathogens through milk and (b) an improvement in preserving its quality.


Butter is composed of about 80% fat and 10-16% water. At first, cream is separated from milk and it is then pasteurized to destroy the micro-organisms present in it. Starter of the bacterial culture is then added which consists of lactic acid bacteria like Steptococcus lactis.

These bacteria curdle and coagulate the milk. Apart from S. lactis other bacteria like Leuconostoc cirtovorum, S. paracitrovorus are also added. These bacteria act on citric acid producing the products, such as diacetyl to impart flavour and aroma. At the required time the ripening is checked by freezing and the product is churned to form butter.


It is another important item of dairy product. It is a concentrated constituent of milk, principally fat, casein and insoluble salts. To retain these constituents in concentrated form, milk is coagulated either by fermenting bacteria, which produce lactic acid, or by the addition of rennet. Fermentation makes the casein spongy, soft and tasty.

Ice Cream

It is made of cream and sugar and contains about 8-14% butter fat. Ice cream also contains some non-pathogenic bacteria.


Microorganisms are of enormous significance in medicine. Some important drugs synthesized by micro-organisms are as follows:


An antibiotic is a substance which is produced by living organisms and has the capacity to inhibit the growth or metabolic activities of other living organisms. Green alga Chlorella produces chlorellin—an antibiotic, which is known to inhibit the growth of several species of bacteria and is effective against other algae. Bacteria and fungi are the well known groups which produce various kinds of antibiotics. Apart from these micro-organisms, certain protozoans, e.g., Paramecium aurelia also produce antibiotic.


Ergot of rye (the sclerotia of Claviceps purpurea) has been used as a drug to induce uterine contraction in case of delayed child birth. This, like almost any other drug, can even fatal if taken frequently or in excess quantity.


This drug has been synthesized by yeasts from benzaldehyde and is often used against troubles and asthma.


They are synthesized by micro-organisms like bacteria and fungi. In 1958, H. A. Barker and H. Weissbarch discovered that cell-free extract of Clostridium tetanomorphum produces vitamin B. It has been discovered recently that Streptomyces griseus and S. aurofacius produce vitamin B. This vitamin is used as a preventive measure against nervous disorder. Fungi like Ashbya gossipy and Eremothecium ashpyi synthesize the vitamin riboflavin which is an important component of vitamin B complex group.


It has been noted that glycerin can be produced commercially by the action of certain yeasts, e.g., Saccharomyces ellipsoideus, on sugar.

Microbes as Pesticides

Certain micro-organisms like bacteria, fungi, viruses, protozoa and even nematodes infect insects and kill them. In other sense they may be called microbial pesticides and they are now being used as means of pest control.