Importance Of Microorganisms Essays

Bacteria are unicellular and ultra-microscopic organisms, yet they play an important role in nature. They are of tremendous importance to man. They play an important role in agriculture and medicine and are the basis of many industries. Some are beneficial to man directly or indirectly, others are very harmful as they cause various plant and animal diseases. Bacteria are considered as our friends and foes due to their beneficial and harmful activities. Their economic importance can be studied under two aspects:

(A) Beneficial aspects.

(B) Harmful aspects.

(A) Beneficial Aspects:

The beneficial activities of the bacteria can be classified as follows:

(1) Role in agriculture.

(2) Role in industry and medicine.

(1) Role in Agriculture:

The activities of bacteria are very important in agriculture in the following aspects:

(a) Decaying of organic substance:

Most of the bacteria are very useful in bringing about decomposition of dead organic matter of plants and animals by the secretion of enzymes. The enzymes convert the fats, carbohydrates and nitrogenous compounds into simpler forms, such as, CO2 water, ammonia, hydrogen sulphide, phosphates, nitrates etc that are used as raw material by the green plants. Thus, these bacteria not only decompose the organic compounds but also remove the harmful waste from the earth and thus function as nature's scavengers.

{b) Fertility of the soil:

Some bacteria maintain and others increase the fertility of the soil. They bring about physical and chemical changes in the soil by converting insoluble materials into soluble ones. These bacteria are the ammonifying, nitrifying and the nitrogen fixing Bacteria.

(i) Ammonifying Bacteria:

The decay bacteria decompose the proieinous compounds into amino acids, which are reduced to ammonia by ammonifying bacteria. The free ammonia combines in the soil to form ammonium salts. This conversion is known as ammonification. Examples are Bacillus ramosus, B. vulgaris etc.

(ii) Nitrifying Bacteria:

These bacteria convert ammonium salts into nitrates, which are absorbed by the plants. The nitrifying bacteria are the Nitrobacter and Nitrosomonas. The Nitrosomonas oxidize the ammonium salts into nitrous acid, which forms nitrites in the soil. The Nitrobacter then converts the nitrites into nitrates. This conversion of ammonium salts into available nitrates is called nitrification.

(iii) Nitrogen Fixing Bacteria:

These bacteria take up nitrogen from the atmosphere and convert it into organic nitrogen compounds. It is known as nitrogen fixation. The nitrogen-fixing bacteria are of two types. One type includes Azotobacter and Clostridium, which live freely in the soil and fix nitrogen of the air in their bodies in the form of nitrogenous organic compounds. The other types of bacteria are the nodule bacteria, the Bacillus radicicola. Rhizobium lives as symbiont in the roots of leguminous plants and forms nodules. These bacteria absorb free nitrogen from the bacterial cell. The leguminous plants thus enrich the fertility of the soil. They are grown for green manuring and rotation of crops.

(2) Role in Industry and Medicine:

Bacteria play a very important role in various industries. The products obtained as a result of bacterial activities cannot be chemically prepared. Their activities are involved in the following industries:

(a) Preparation of Alcohols:

Ethyl alcohol and butyl alcohol are manufactured by the bacterial acivities in the sugar solution, e.g., Clostridium acetobutylicum.

(b) Preparation of Vinegar:

Vinegar is prepared by the activities of Acetobacter aceti in the sugarcane juice.

(c) Preparation of Butter, Cheese etc.:

The preparation of butter, cheese etc. is done by bacteria. The Lactobacillus lactis is responsible for souring of milk resulting in curd (dahi) preparation. Bacterial activities also impart the typical flavours.

(d) Preparation of Tea, Coffee etc.:

Bacteria are very useful in preparation and flavouring of tea, coffee, cocoa etc. e.g., Micrococcus.

(e) Preparation of Tobacco:

Tobacco leaves are cured and flavoured by the bacteria. Typical types of bacteria are cultured for this purpose, e.g., Micrococcus.

(f) Preparation of Hemp fibres:

Fibres from the hemp are isolated after rotting the stems by activity of bacteria (e.g., Clostridium butyricum). The bacteria eat up the protoplasmic tissues but leave the sclerenchyma fibres.

(g) Preparation of Leather and Tanning:

The hairs and fats are removed from the skin by the action of bacteria in the leather industry.

(h) Preparation of Antibiotics:

The bacteria are also used in the preparation of antibiotics. According to Sir Alexander Fleming, the growth of harmful Staphylococcits is checked by Penicillium natatum. With this discovery, large number of antibiotics has been prepared which are of great importance in the medical world. Tyrothricin, Subtillin, Polyximin-B, Bacitracin, Streptomycin, Aureomycin, Terramycin are some well-known antibiotics.

(B) Harmful Aspects:

Bacteria are also harmful to man directly or indirectly. They cause various diseases in plants, human beings or domestic animals. The harmful bacteria are of the following types ;

(i) Animal pathogenic Bacteria.

(ii) Plant pathogenic Bacteria.

(iii) Food destroying Bacteria.

(iv) Soil fertility destroying Bacteria.

(i) Animal Pathogenic Bacteria:

There are a large number of parasitic bacteria, which cause various serious diseases in man and domestic animals, sometimes in epidemic form. They arc invisible enemies. Some of the common human diseases producing bacteria are Mycobacterium tuberculosis causing tuberculosis, Eberthela typhosa causing typhoid, Clostridium tetani causing tetanus, Shigella dysenteriae causing dysentery, Hemophilous influenzea causing influenza, Corynebacteriaum diphtlteriea causing diphtheria, Diplococats pneumonias causing pneumonia, Vibrio cholerae causing cholera, Streptococcus causing blood poisoning, Treponema pallidium causing syphilis, Gonococcus causing gonorrhoea, Bacillus pestis causing plague etc. In domestic animals various diseases are caused by bacteria, e.g., Anthrax, Pneumonia, Tuberculosis, Cholera, Glanders etc.

(ii) Plant Pathogenic Bacteria:

Many parasitic bacteria cause serious diseases in cultivated plants, which cause great harm to the crops. Important diseases are Citrus canker, fire blight of pear, cotton root rot, walnut blight, potato rot, pineapple rot etc. The Canker of Citrus (orange and lemon) is caused by Xanthonionas citri. The rot diseases cause black spots on potato, tomato, cabbage, carrot etc.

(iii) Food destroying Bacteria:

Some saprophytic bacteria are responsible for the decay of human foodstuffs including meat, milk, vegetables, fruits etc. These bacteria spoil foodstufs and make them unpalatable and poisonous, e.g., souring of milk, rotting of meat, vegetables, fruits etc. Staphylococcus and Clostridium botulinum cause food poisoning when rotten food is eaten,

(iv) Soil Fertility destroying Bacteria:

These are denitrifying bacteria in the soil, which reduce the nitrates, and the ammonium salts to free nitrogen, which escapes into the atmosphere. This process is known as denitrification, which decreases the fertility of the soil, e.g., Bacillus denitrificans.

These bacteria are often abunbant in the poorly drained and heavily manured soil. So the denitrifying bacteria are the natural enemies of the farmers.

Thus with the study of economic importance of bacteria we conclude that bacteria are our friends due to their beneficial aspects and enemies due to their harmful aspects. But in the bacteria beneficial aspects overweigh their harmful aspects. We can control the harmful activities but their beneficial activities cannot be replaced by artificial processes. So the bacteria are our friends more and enemies less.



Micro-organisms Micro-organisms (or microbes) are literally microscopic organisms, which can only be seen properly with the aid of a microscope. These include bacteria, microscopic fungi (moulds) and protoctists. Although viruses, which are even smaller than bacteria, are generally considered to be non- living entities, they might also be included here as they are important disease-causing agents. Micro-organisms are the most numerous organisms in any ecosystem. There are about 159,000 known species, although this is thought to be less than 5% of the total in existence. There is vast genetic diversity among micro-organisms, which is not surprising as they began evolving over a billion years before land plants. This, coupled with their small size and reproduction, helps explain why micro-organisms, particularly bacteria, are the most widely distributed forms of life on the planet. While many are cosmopolitan species, others exist in habitats totally inhospitable to larger organisms. There are species of bacteria able to grow in hot springs up to 90° C, others live below freezing point in Antarctica, in soda lakes, anaerobic situations, and sites with high concentrations of metals, sulphur and other normally toxic compounds.


and people Micro-organisms are of immense importance to the environment, to human health and to our economy. Some have profound beneficial effects without which we could not exist. Others are seriously harmful, and our battle to overcome their effects tests our understanding and ingenuity to the limit. However, certain micro-organisms can be beneficial or harmful depending on what we want from them: saprophytic decomposers play an important role in breaking down dead organic matter in ecosystems, but these same micro- organisms can be responsible for food spoilage (rotting, going bad, going off) and subsequent illness.


micro-organisms Disease and decay are not inherent properties of organic objects, nor do they result from physical damage or being eaten by insects, it is micro- organisms that bring about these changes. We are surrounded by bacteria, viruses, protoctists and fungi. Many cause disease in farm animals and commercial crops, many others are capable of invading our bodies and causing human disease.

Examples of familiar human diseases include:

Bacteria: salmonella, tetanus, typhoid, cholera, gangrene, bacterial dysentery, diphtheria, tuberculosis, bubonic plague, meningococcal meningitis, pneumococcal pneumonia

Viruses: rabies, influenza (flu), measles, mumps, polio, rubella (german measles), chicken pox, colds, warts, cold sores

Protoctists: malaria, amoebic dysentery

Fungi: athlete's foot, ringworm

These disease-causing organisms are called pathogens and we often refer to them in everyday, non-scientific terms as ‘germs’ or bugs. Each disease has a specific pathogen, i.e. different diseases are caused by different kinds of germ. If the disease organism can be transmitted from one person to another it is said to be infectious. Non-infectious diseases, such as allergies, cancer, vitamin deficiency, and mental illness may develop when the body is not functioning properly.

Common infectious diseases can be spread (or be caught) by consuming food or water containing pathogens or their toxic products (e.g. salmonella, typhoid, cholera ); by ‘droplet infection’, which is inhaling or ingesting droplets of moisture which have been breathed, coughed or sneezed out by an infected person (e.g. colds, flu); by entry through a wound or sore (e.g. tetanus); by direct contact with an infected person (e.g. athletes foot, ringworm). Some pathogens are carried by vectors from one organism to another. For example: mosquitoes carry the malaria protoctistan; rat fleas carried the bacterium that caused the Black Death; houseflies can spread micro-organisms from faeces to our food. The vectors should not be confused with the pathogenic organisms that they are carrying.

We are usually able to develop immunity to infections by virtue of our immune system. Our blood produces specific antibodies in response to the presence of specific foreign bodies called antigens. These antibodies gradually proceed to destroy the invading organisms. However, over 40% of all deaths in developing countries, including the annual deaths of 14 million children, are caused by infectious diseases. In developed countries, where there are good medical services, people seldom die from infectious diseases. Diseases can be prevented or cured. Prevention is principally through improved standards of hygiene, personal health and the development of vaccinations. Vaccines contain killed or non-virulent (less pathogenic) strains of bacteria and viruses, and when these are injected into the blood, or swallowed, the body has a mild form of the disease, and is able to manufacture sufficient antibodies to acquire immunity. This is the process of immunisation, and vaccinations are an effective way of stimulating the body's defence against such diseases as diphtheria, polio, measles, mumps, german measles, tetanus, tuberculosis and hepatitis B. Vaccinations do exist for flu, but these have to be continually developed, because flu virus antigens are frequently changing, producing new strains of virus to which people are not immune. New strains can result in a flu epidemic.

Most bacterial infections can be treated with antibiotics which are chemicals extracted from fungi or other bacteria. Penicillin was the first antibiotic drug. It was discovered by Alexander Fleming (1881 - 1955), isolated from the Penicillium mould, and commercially produced using biotechnology. They can be swallowed or injected to kill internal bacteria or prevent them from multiplying, although this is not an instantaneous process. However, as we use more and more antibiotics, some bacteria are becoming resistant to them. One strain of Staphylococcus aureus is resistant to all known antibiotics except one, but this drug can have dangerous side-effects. Contributing factors to this resistance include the over-prescribing of antibiotics for people and for farm animals, and patients not finishing their course of the drugs. Antibiotics cannot treat viral infections, and yet many people expect their doctors to prescribe antibiotics for colds and flu, which of course are viral.

Disinfectants, such as bleach, are powerful chemicals used to kill micro-organisms in the environment. Antiseptics are weaker chemicals applied to wounds and sores to prevent micro-organisms from multiplying. Specific fungicidal chemicals are effective against the few fungal micro-organisms that live on our skin such as ringworm and athlete’s foot.

Useful micro-organisms:

Decomposers Fungi and most bacteria are saprotrophic and have an important role in an ecosystem as decomposers, breaking down dead or waste organic matter and releasing inorganic molecules. These nutrients are taken up by green plants which are in turn consumed by animals, and the products of these plants and animals are eventually again broken down by decomposers.

Sewage treatment employs bacteria which break down harmful substances in sewage into less harmful ones. Aerobic bacteria decompose organic matter in sewage in the presence of oxygen. Once the oxygen is used up the aerobic bacteria can no longer function, and anaerobic bacteria continue the decomposition of organic matter into methane gas and carbon dioxide, along with water and other minerals. The digested sludge is rich in nitrates and phosphates and can be spread on the land as fertiliser. Some sewage treatment plants have used the methane as a cheap form of fuel (biogas). Anaerobic micro-organisms are also being used to convert carbohydrate-rich crops, such as cane sugar and maize, into ethanol which is used as a substitute for petrol in cars. This biofuel (or gasohol) is used widely in Brazil, which has meagre oil resources.

The carbon cycle Fats, carbohydrates and proteins all contain carbon atoms, so dead and waste organic matter contains a lot of carbon. In breaking this down, saprophytic bacteria and fungi take up some carbon to build their own bodies, and release some as carbon dioxide during respiration. However, the carbon cycle need not involve decomposers because autotrophs can access carbon from the abundant carbon dioxide in the air.

The nitrogen cycle All living things need nitrogen, it is an essential component of all proteins. It makes up 79% of the air we breathe, but the N2 molecules are very stable and unreactive, and are not readily accessible to plants and animals in this form. Nitrogen-fixing bacteria are able to convert (or fix) nitrogen gas from the air into nitrogen compounds. Plants take up these nitrogen compounds through their roots, combine them with products of photosynthesis, and make proteins. Animals obtain the protein they need by eating the plants or other animals. Some nitrogen-fixing bacteria are free- living in the soil, others live in small swellings, or nodules, on the roots of some plants, particularly members of the legume family (such as clover, peas and beans). This is a symbiotic arrangement, the plant gets nitrogen compounds and the bacteria receive carbohydrates from the plant. Dead and waste organic matter contains ammonium compounds which are converted by nitrifying bacteria into nitrates, and these are assimilated by plants. Denitrifying bacteria remove nitrates and ammonium compounds from the soil by converting them into nitrogen gas.

Digestion Despite the vast quantities of cellulose eaten by herbivores, mammals themselves cannot digest cellulose and rely entirely on the action of carbohydrate-digesting bacteria in their guts. These secrete the enzyme cellulase which splits the cellulose into monosaccharides which can be absorbed by the gut. Ruminants (cud-chewing) mammals such as cows have a large chamber in the stomach called a rumen which contains huge numbers of these bacteria. Non-ruminant herbivores such as rabbits and horses have cellulose-digesting micro-organisms in their appendix and caecum which act as ‘fermentation-chambers’. Huge numbers of bacteria, particularly Escherichia coli, also inhabit the human colon. There are an estimated four hundred species and it has been suggested that the action of some of these on carbohydrate can contribute up to 10% of our energy requirements. Other bacteria synthesise vitamins and amino acids, and others may contribute to our resistance to disease by competing for space in the gut with harmful bacteria. It is important therefore to maintain a healthy gut flora.

Biotechnology The manipulation of cells, particularly micro-organisms, to produce useful substances is referred to as biotechnology. Micro-organisms are exploited extensively in the fields of medicine, agriculture, food production, waste disposal and many other industries. We make use of some saprophytic bacteria which do not produce waste products harmful to humans. The bacterium Lactobacillus feeds on milk, turning it into yoghurt. Other bacteria and fungi help in cheese-making and are responsible for distinctive flavours. Most industrial enzymes (protein catalysts) come from micro-organisms. Special strains of fungi and bacteria are developed by genetic engineering. They are grown in large fermenters where they secrete enzymes into their nutrient solution. The enzyme is isolated and concentrated for use. Examples of such enzymes include amylases for producing chocolates, fruit juices and syrups; cellulases for softening vegetables; proteases for tenderising meat and for removing biological stains when put in biological washing powders.

Yeast is a single-celled fungus that lives naturally on the surface of fruit. It is economically important in brewing and bread-making. Yeast respires anaerobically (i.e. without the use of oxygen) and breaks down glucose with the production of carbon dioxide, ethanol (alcohol) and energy. In wine-making the yeast feeds on fruit sugars in the grapes, and in beer-making it feeds on the maltose sugar in germinating barley. The term fermentation, is usually applied to this process of anaerobic respiration in which alcohol is produced. Controlled oxidation of alcohol can be carried out to produce vinegar (ethanoic acid). Bread-making uses the carbon dioxide produced by anaerobic respiration, not the ethanol. Starch in the dough breaks down to sugar, which feeds the yeast. The carbon dioxide bubbles make the dough rise before it is baked into bread.

Yeast, including that left over from brewing, and other micro-organisms are also cultivated as an important food source for farm animals, and for humans. When fed on simple sugars and inorganic salts in controlled conditions, these micro-organisms can double their mass within hours (plants and animals may take weeks). They are rich in protein and contain most of the essential vitamins and amino acids required by animals. The mould Fusarium is grown in this way to form a mycoprotein which is as nutritious as meat, but lower in cholesterol and higher in fibre. It is marketed as the meat substitute ‘Quorn’. This kind of high protein food produced from micro-organisms is called single-cell protein, and it is increasingly grown on the nutrients present in industrial waste (e.g. from food, paper-making and agricultural industries).


micro-organisms Micro-organisms can be grown in a sterile Petri dish on agar jelly which contains appropriate nutrients. After introducing a small sample of water, soil, leaf, etc., the lid should be permanently sealed. After several days the micro-organisms will have grown and multiplied. The colonies become visible due to the multiplication of the cells, not due to cells getting larger! Fungi usually appear as furry clumps and bacterial colonies are often smooth and shiny-looking. After inspection, the sealed dishes should be sterilised in an autoclave or strong disinfectant, in case any pathogens have been incubated.


Diversity of organisms
Ecosystems and habitats
Species interaction
Self assessment (1)
Self assessment (2)

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