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Microorganisms are studied for diverse reasons. These microscopic forms of life play tremendous significant roles in the natural environment. They are ubiquitously found in all environments including aquatic, terrestrial and arboreal habitats as well as in hot springs and icebergs where life rarely exists. Microorganisms harbour many beneficial qualities, and these features of theirs have been exploited by man since time immemorial and even till date to improve the quality of life and in the production of diverse products that are of medical, industrial, pharmaceutical and economic importance. However, some microorganisms are not beneficial to man, plants and animals because they cause infections and diseases in them. A handful of microorganisms including bacteria, fungi, viruses and protozoa are pathogenic microorganisms because they cause disease in man and other animals. In this section, some of the benefits of microorganisms to man and his environments, aside their deleterious and harmful activities have been highlighted. 


  • Biodegradation: Biodegradation is the breaking down of substances such as organic matters including biological and environmental wastes through the activities of microorganisms. It is synonymous to bioremediation – which is the biotechnologically-driven method of cleaning-up pollutants in the environment (for example, oil spillage) using certain group of microorganisms. Bioremediation is the technique of cleaning up environmental pollutants based on the capacities of microorganisms to degrade and store chemical compounds. Virtually all naturally-occurring organic compounds can be degraded or broken down by some microorganisms including but not limited to Pseudomonas and Bacillus species. Chemicals found in gasoline and oil spills are eaten up by microbes, and as such these organisms are employed in cleaning up the environment whenever they are contaminated by such pollutants. Pseudomonas is an example of microorganism that has been exploited for this particular purpose. When microorganisms feed on or digest these pollutants such as oil spills; water, carbon dioxide and other harmless and environmentally friendly products are produced and released into the environment. Both biodegradation and bioremediation are safe because they make use of natural processes (i.e., the metabolic and degradative potentials of microorganisms) to clean up a polluted environment. In most developed countries, microorganisms have been exploited in waste management activities including landfills, sewage degradation, and sludge processing and composting activities.
  • Food spoilage: Due to their ubiquity, microorganisms cause food spoilage in foods and grains or other unprocessed food including those stored in the refrigerator or sold in supermarkets. Cooked food and already processed food are not left out as they can also be attacked by microbes particularly fungi. Food contamination by microorganisms (especially bacteria and fungi) has been a source of infections in human population. Typical examples of such infection that can result from food contamination by microbes include food poisoning – which usually occurs after the consumption of food contaminated by microbes. Microorganisms thrive in food because most foodstuffs especially the processed ones contain some of the nutritional requirements that encourage the growth of microbes. 
  • Production of foods: Though they may cause food spoilage and disease, microorganisms has been exploited in the production of a handful of beverages, fermented and non-fermented food products for man and animals. Food products manufactured through the metabolic activities of microorganisms include yoghurt, beer, cheese, bread, wine, vinegar, and probiotics. Probiotics are microbial culture preparations which help to promote good health in humans by inhibiting pathogens and promoting good health in the recipient host particularly in the gastrointestinal tract (GIT).
  • Recycling of nutrients in the ecosystem: Nutrients including oxygen, carbon, nitrogen, sulphur and phosphorus to mention but a few are generally recycled in nature through the activities of some group of microorganisms through the process of biogeochemical cycling. Some of these elements/nutrients exist in complex molecular forms that cannot be utilized by living organisms, and thus must be broken down into simpler forms that can be shared and used by these organisms including humans and plants. This is only made possible through the metabolic activities that occur in microorganisms which make them able to recycle these elements in nature, and thus make them available for other forms of life. Both fungi and bacteria play critical roles in the recycling of nutrients in the ecosystem, and these groups of microorganisms are very important in agriculture because of their degradative and recycling activities.
  • Digestion of nutrients in man and animals: Microorganisms play significant role in the breaking down of food molecules in the body of both man and animals. For example in ruminant animals (i.e., animals with four chambered stomach such as cow), microorganisms in the rumen of these animals helps to breakdown food nutrients. They are also sources of carbon, vitamins and other proteinous substances. Bacteria found in the rumen of animals also help to breakdown cellulose (an indigestible form of carbohydrate found mainly in plants) by producing enzymes (for example, cellulase) that carries out this important activity of cellulolysis. Cellulolysis is the enzymatic breakdown of cellulose-containing plants or materials by the activities of microbes using cellulase. 
  • Promotion of health and nutrition: Bifidobacterium and Lactobacillus are two important bacteria that exist in the gastrointestinal tract (GIT) of humans – where they are widely believed to synthesize vitamins and other important nutrients which helps to boost the health of man. These microorganisms in addition to many others also help to protect the body against infections by preventing the multiplication of pathogenic microorganisms in the gut or GIT. In the female vagina for example, Lactobacillus acidophilus is a bacterium that colonizes the vaginal wall and it helps to prevent the invasion of pathogens by creating a low pH which makes that particular environment (i.e., the vagina) hostile to colonization by pathogenic bacteria and fungi.     
  • Biomedical research applications: Saccharomyces cerevisiae (a fungus) and Escherichia coli (a bacterium) are two of the most exploited and widely studied forms of microorganisms whose metabolic activities have been exploited and harnessed by man to manufacture a variety of useful products as well as unravel some of the mysteries surrounding some infectious diseases in man. Information’s from these microbes are used as models for studying other cellular forms of lives including physiologic and biological information’s that pertains to both prokaryotic and eukaryotic cells. 
  • Production of biofuels: Microorganisms (yeast and bacteria inclusive) are currently exploited in fermentation processes or industries to convert carbohydrates such as cassava to produce biofuels (for example, ethanol) which is used for various industrial and domestic purposes. In some developed economies, biofuels are currently used to fuel cars; and it is believed that in the nearest future, biofuels may replace premium motor spirit (PMS) otherwise known as “car fuel” since biofuels are cleaner forms of energy than PMS.
  • Medical purposes: In medicine, microorganisms have played significant roles in the alleviation of man’s plights in the face of infectious diseases. Most significant was the discovery of penicillin (the first antibiotic), a by-product of Penicillium notatum cum P. chrysogenum (a fungus). Penicillin was serendipitously discovered by Alexander Fleming, a famous microbiologist in 1928; and this antimicrobial agent is an antibiotic used till date mainly for the treatment of bacterial related infections. A handful of antibiotics used today in clinical medicine were initially sourced from microbial cells (bacterial and fungal cells in particular), even though some are synthetically produced today. Microorganisms including Bacillus, Streptomyces, and Penicillium to mention but a few synthesize antimicrobial agents. Antimicrobial agents are basically substances produced by microbes, and which inhibit or kill other microorganisms that are pathogenic in nature. Despite the growing level of resistance, microorganisms have continued to be a source of antibiotics used for the treatment of infectious diseases in both veterinary and human medicine. Microorganisms (particularly viruses and bacteria) are also a source of vaccines which are used in humans and animals as a preventive or prophylactic measure against infectious diseases.

Further reading

Brooks G.F., Butel J.S and Morse S.A (2004). Medical Microbiology, 23rd edition. McGraw Hill Publishers. USA. Pp. 248-260.

Madigan M.T., Martinko J.M., Dunlap P.V and Clark D.P (2009). Brock Biology of microorganisms. 12th edition. Pearson Benjamin Cummings Publishers. USA. Pp.795-796.

Nester E.W, Anderson D.G, Roberts C.E and Nester M.T (2009). Microbiology: A Human Perspective. Sixth edition. McGraw-Hill Companies, Inc, New York, USA.

Prescott L.M., Harley J.P and Klein D.A (2005). Microbiology. 6th ed. McGraw Hill Publishers, USA. Pp. 296-299.

Singleton P and Sainsbury D (1995). Dictionary of microbiology and molecular biology, 3d ed. New York: John Wiley and Sons.

Slonczewski J.L, Foster J.W and Gillen K.M (2011). Microbiology: An Evolving Science. Second edition. W.W. Norton and Company, Inc, New York, USA.

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