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Applications of Microbiology. Application of Microbiology in Agriculture, Industry, Medicine, pollution control in air, soil and water:

Uses of Virus:

(1) Cyanophages are used in the control of water blooms.

(2) Ganga water is believed not to be spoilt because of the presence of phages in it.

(3) Attenuated viral doses are used in vaccine against specific diseases.

(4) Viruses are useful to geniticists as they bring about transduction and help to establish that DNA is a genetic material.

Economic Importance of Bacteria:

(A) In Agriculture:

Some bacteria increase soil fertility. The plants take nitrogen in the form of nitrates. In soil nitrates are formed by three processes:

(i) By Nitrogen-Fixing Bacteria:

Bacteria are found in soil either free, e.g. Azotobacter and Clostridium or in root nodules of leguminous plants; e.g., Rhizobium leguminosarum. These bacteria are capable of converting atmospheric free nitrogen into nitrogenous compounds.

(ii) Nitrifying Bacteria:

These bacteria convert nitrogen of ammonia into nitrite (NO₂) e.g., Nitrosomanas and convert nitrite compounds into nitrates e.g. Nitrobacter.

(iii) Decay of Dead Plants and Animals:

Some bacteria attack dead bodies of plants and animals and convert their complex compounds into simpler substances, e.g. carbondioxide (CO₂), water (H₂O), nitrate (NO,) & sulphate (SO₄).

(B) In Dairy:

Bacterium lactici acidi and B. acidi lactici are found in milk. These bacteria ferment lactose sugar found in milk to form lactic acid by which milk becomes sour. If the milk is heated at 62.8°C for 30 minutes and is simultaneously cooled the number of lactic acid bacteria is reduced but all spores and cells of these bacteria are not destroyed and pathogenic spores are destroyed. In this way milk becomes sour but it takes longer time to become sour than ordinary milk. This process is known as pasteurization.

Lactic acid bacteria bring together droplets of caesin, a protein found in milk help in the formation of curd.

On churning of curd, butter is derived in the form of fat’s rounded droplets & the butter on heating is converted into “ghee”. On freezing of caesin of milk protein, it is fermented by bacteria with the result that foamy and soft substances, different in taste is formed.

(C) Industrial Value:

From industrial point of view, bacteria are most important. Some of the uses of bacteria in industries are as follows:

(i) Vineger Industry:

Vineger is manufactured from sugar solution in the presence of Acetobacter aceti.

(ii) Alcohol c£ Acetone:

Clostridium acetobutyllcum takes part in the manufacture of butyl alcohol and acetone.

(iii) Fibre Ratting:

By this process, fibres of jute, hemp and flax are prepared. In the preparation of flax, hemp and jute; the ratting of stems of Linum ustiatissimum (Flax = Hindi: Sunn), Cannabis sativa (Hemp = Hindi: Patson) and Corchorus capsularis (Jute) respectively is done. In this process the stems are kept under water for some days and when stems begin to decay, fibres are separated from the stem on thrashing. The process of separation of fibres is known as ratting. This process is carried out by Clostridium butyricum inhabiting the water.

(iv) In Tobacco Industry:

Bacillus megathenium mycococcus is used for its fermentative capacity for developing flavour and taste in tobacco leaves.

(v) In Tea Industry:

By fermentative action of Mycococcus condisans curing of tea leaves is done. By this process special taste is developed in tea leaves.

(vi) Tanning of Leather:

Some bacteria decompose fats which are found in skin of animal with the result that skin and hair are separated from each other and this leather becomes ready for use.

(D) Medicines:

Some of the antibiotics are manufactured by bacteria actions, e.g. Bacillus brevis- antibiotic thyrothricin, B. subtilis-antibiotic subtelin. Vitamin B is manufactured by fermentative action of Clostridium acetobutylicum. Some of the antibiotics obtained from different species of Streptomyces are given below:

Name of Antibiotic Bacteria from which derived

1. Streptomycin Streptomyces grisieus

2. Chloromycin S. venezuelae

3. Aureomycin S. aureofaciens

4. Terramycin S. rimosus

5. Neomycin S. fradiae Viral Vaccines

When an animal is injected with killed (inactivated) or severely weakened (attenuated) viruses (the substance injected is called ‘viral vaccine’), the latter induce the animal’s defence system to make antibodies against the proteins of injected viruses. Thesre antibodies tend to protect the animal against infection by the same virus. Viral vaccines are of two types, (i) Live vaccines: those which are prepared from live, avirulent or severely weakened (attenuated) viruses and (jj) Killed vaccines: those which are prepared from killed inactivated viruses.

(E) Pollution Control:

In the present day world environmental pollution poses a great threat to the lives of living beings and natural environment. Sewage, oil-spills, pesticides, herbicides, chemical effluents and heavy metals are just some of pollution hazards.

However, biotechnology gives a hope for controlling the pollution hazards, the biotechnical processes directed towards the control of pollution primarily aim at destruction of specific raw materials of pollution, i.e. the pollutants. This aim can be achieved in the following ways:

(i) Microorganisms can be deployed as voracious scavengers removing all manner of pollutants. For example: (a) various strains of Pseudomonas can consume hydrocarbons of oil & petrol, however each individual strain can consume only one or a few of the many different types of hydrocarbons.

The genes that code for enzymes which attack hydrocarbons are not found on the main bacterial chromosome but on plasmids. No single strain of Pseudomonas can consume all varieties of hydrocarbons constituting oil because the same does not contain all the genes that code the enzymes which attack the hydrocarbons varieties.

Anand Chakrabarty (1979), an India, born American scientist created a single strain of Pseudomonas that would be able to consume all the genes responsible for oil consumption and thus mop up all the types of hydrocarbons in the oil. This unique bacterial strain, the product of genetic engineering is called a SUPERBUG.

This superbug was created by introducing plasmids from different strains of Pseudomanas into a single cell. Also the use of mixture of strains of bacteria has been successfully used to clear up oil contaminated water from oil spills from ships and clearing up water supplies.

(b) Mixture of bacterial strains is also being used to clear up other pollutions. An impressive example is the removal of grease deposited on the inside of a holding tank of a ship. The same tank becomes grease free after four and half month’s operation during which ‘mixtures’ of bacterial strains were added.

These bacteria very efficiently prevented the buildup of grease on the tank’s interior. However, this kind of use of bacterial strains mixtures may prove significant in factories which process meat and poultry where pipes and vessels can become plugged with grease.

(c) New chemicals (such as pesticides, herbicides), and the substances which previously appeared on the Earth’s surface only in small amounts (such as oil, many metals) tend to persist since few of the common microorganisms in soil or water can use them as food.

This has created a growing demand for tailor made packages of microorganisms which can consume such specific forms of pollutants. Several major companies, especially in United States, manufacture mixtures of microorganisms and enzymes designed to clean-up chemical wastes like oil, detergent, waste waters from paper mills and highly toxic materials such as dioxin, the chemical that wreaked havoc on the town of Seveso (Italy).

(ii) The root cause of pollution i.e. the sources of pollution should be attacked. For example, some bacteria convert organic faecal substances e.g. cow- dung, decaying leaves of plants into manure and humus. Municipal sewage treatment systems which are generally operated in most of the towns and cities carry out various steps involved.

These steps are namely, primary (or mechanical) treatment, secondary (or biological) treatment and tertiary (or final) treatment. Secondary or biological treatment is a purely biological treatment of mechanically treated sewage and concerns microbial activity.

This treatment accomplishes two important phases, namely aerobic phase and anaerobic phase. The aerobic phase consists of aerobic digestion of sludge by various filters (e.g. trickling filters), oxidations ponds and activated sludge process, and the anaerobic phase is represented by anaerobic digestion of sludge.

(a) Trickling filters generally consists of 6-10 feet deep bed of crushed stone, gravel, slag or similar material. The sewage effluent is sprayed over the surface of the bed, the spraying saturates the effluent with oxygen. The bed surface becomes coated with aerobic microbial flora consisting of microalgae, microfungi, bacteria and protozoa. As the effluent seeps over, the aerobic microbes degrade the organic matter.

(b) Oxidation pond sewage treatment is recommended for small communities in rural areas. Oxidation ponds (also called Lagoons or Stabilization ponds) are generally 2-5 feet deep shallow ponds designated to allow direct wind action and algal growth on the sewage effluent.

Oxygen supplied from air and produced as a result of algal photosynthesis fulfils biochemical oxygen demand (BOD) of sewage effluent and thus helps in maintaining aerobic condition in sewage effluent. In such condition the aerobic microorganisms grow rapidly and digest organic matter. Chlorella pyrenoidosa is a common algal representative grown in oxidation ponds.

(c) In Activated Sludge process the mechanically treated sewage effluent is pumped into a sedimenta­tion or setting tank wherein the sewage floes and settles out. A portion of sewage floe is returned to activate a new batch of mechanically treated sewage effluent and the rest is pumped to activate sludge digester where air is blown by several jets. Thus in the presence of plentiful oxygen, oxidation of sewage effluent is brought about by aerobic microorganisms which break down organic matter to carbon dioxide and water. Now the effluent is passed through a sedimentation tank and about 10% of organic matter of the effluent in digested via this process.

The sludge collected after primary treatment of sewage is subjected to anaerobic digestion in a separate tank designed specially for the purpose. Since anaerobic conditions prevail in this tank, the anaerobic microorganisms bring about digestion of organic matter by degrading them to soluble substances and gaseous products (methane 60-70%, C0₂ 20-30%, and smaller amounts of H₂ & N₂). This gas mixture can be used for operating power of the sewage plant or as a fuel. Recently, the Municipal Corporation of Delhi (India) has started supplying this gas mixture to about 100,000 people for cooking purposes.

(d) Heavy Metal’s Pollution Control:

Certain heavy metals like mercury, lead and cadmium are among the most harmful pollutants disposed off in waste-effluents by modern industries. Mercury causes metal poisoning which attacks the nervous system of patients. Though heavy metals are as toxic to most types of micro organisms as they are to animals including humans, there are some algal and bacterial species which avidly extract these metals from their surrounding. Biotechnologists are creating new biotechnological methodologies which could be used to purify metal laden effluents.

The biotechnologists are seriously thinking to grow metal-extracting forms of microorganisms, particularly algal forms, in ponds filled with heavy metal containing factory effluents and suitable nutrients. This would allow the microorganisms to extract metals from their surroundings and sequester them inside their cell membrane.

Finally, these microorganisms would be filtered from their liquid environment and deposited in special dumps, e.g. Thiobacillus bacteria can accumulate silver. A certain amount of silverminevitably appears in waste waters from film factories and other industrial sites. The Thiobacillus bacteria could collect this wasted silver and provide it for re use. This way they could reduce the losses of this expensive resource.

(e) Acid rain Pollution Control:

Sulphur-dioxide, an air pollutant is produced when materials containing sulphur, especially coal, are burned. Sulphur dioxide when released into the air, dissolves in water droplets and forms sulphuric acid (acid rain). Its harmful effects are partly attributable to a lowering of pH and partly because it releases soluble aluminium salts into the environment in toxic quantities.

However, the acid rain accumulates in lakes scattered generally in a wide area of hundred kilometers from the source of pollution, and kills fish and plants in vast numbers. Several types of bacteria, specially those that inhabit hot water springs have a great appetite for sulphur compounds, from which they derive energy. If such bacteria are put to coal, their activities would separate much of the sulphur from high-sulphur coal. This would result in sulphur free coal.

(iii) Biotechnological production methods, which are intrinsically less polluting, can be employed to replace conventional methods. By this the hazards of pollution can be brought very much under control. For instance, the conventional processes for manufacturing chemicals for the plastic industry use oil based raw material, some of which inevitably escape to pollute the environment.

This can be checked by replacing the conventional methods by biotechnological methods in which, however, microbes are fed on innocuous raw materials, e.g. sugars (glucose) in manufacturing chemicals for the plastic industry. Another example is that, at present, the conversion of alkenes to alkene oxide (which is used for polymerization form plastics) is accomplished by purely chemical techniques but use of microbial enzymes for this conversion is on the horizon. A Californian firm, namely, Cetus employs a series of three microbial enzymes.

Alkene oxide A more promising biotechnological process to convert alkenes to alkene oxides has been patented in 1981 by scientists from the Waswick University (UK). These scientists discovered a bacterium namely Methylococcus capsulatus which can add oxygen to alkenes.

When this microorganism is supplied with ethylase or propylene gases, it inserts an oxygen atom into each molecule of these gases to produce ethylene oxide or propylene oxide respectively. This is thermophillic bacteria which lives upto 45°C, upto which the oxides are gaseous and it is much simpler to collect product as a gas than as liquid because the latter is mixed in with all the other materials in fermentation apparatus.