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Viruses are non-cellular microorganisms that consist of nucleic acid (DNA or RNA) and proteins. They can only replicate within aliving cell, including cells of animals, plants and bacteria. A virus contains either an RNA or a DNA as its genome. No virus contains both DNA and RNA as its genome. The size of viruses ranges from 0.015 µm to 0.2 µm and they can only be seen under an electron microscope because of their extreme small size. Viruses are lacking in cellular components necessary for their independent reproduction or metabolism; and this is why viruses replicate or multiply inside a living host cell. Outside a living cell they remain dormant and inactive. Viruses cause diseases in man, plants and animals; and some viruses such as the bacteriophages or phages infect other microorganisms such as bacteria. The ability of bacteriophages to infect bacteria has been exploited in industrial microbiology to pass on unique genetic traits from one organism to another especially in the production of an important metabolite in large amount.

A virion is defined as an individual virus particle. Because a virion contain only one type of nucleic acid as its genome (DNA or RNA), viruses can be classified into two classes based on their nucleic acid genome. Thus, they are DNA viruses (whose genome is only made of DNA) and RNA viruses (that only contains RNA as its genome). Viruses are not cells and they do not contain organelles as is applicable in bacteria, fungi, protozoa and algae. Viruses are not cultured in the artificial culture media like the prokaryotic and eukaryotic cells. They are cultured in living cells such as in embryonated egg cell. Viruses can also be cultured in vitro in environments that replicate or emulate the internal environments of living cells. Cell culture techniques containing cell lines of living cells extracted from plants, animals or humans is an example of in vitro techniques employed in the cultivation or study of viruses.


  • Viruses are employed in the production of different vaccines used medically to prevent viral diseases or infections. When introduced into the human body especially prior to the exposure to pathogens or diseases, vaccines and vaccine products helps to protect vaccinated individuals against diseases that are communicable in nature (i.e. diseases that can be transferred from person to person). These vaccines are preparations of dead or attenuated (weakened) viruses – which when introduced into the body of a susceptible human host, has the ability to protect such an individual from contracting or getting an infectious communicable) disease.   
  • Viruses are sources of important enzymes such as reverse transcriptase used in molecular biology or biotechnology processes for the production of important drugs and other pharmaceuticals.
  • Viruses can act as gene vectors for the useful production of useful proteins such as interferons.

Further reading

Bushell M.E (1998). Application   of   the   principles   of   industrial   microbiology   to   biotechnology (ed. Wiseman, A.) Chapman and Hall, New York.

Byong H. Lee (2015). Fundamentals of Food Biotechnology. Second edition. Wiley-Blackwell, New Jersey, United States.

Frazier W.C, Westhoff D.C and Vanitha N.M (2014). Food Microbiology. Fifth edition. McGraw-Hill Education (India) Private Limited, New Delhi, India.

Jay J.M (2005). Modern Food Microbiology. Fourth edition. Chapman and Hall Inc, New York, USA.

Bushell M.E (1998). Application   of   the   principles   of   industrial   microbiology   to   biotechnology (ed. Wiseman, A.) Chapman and Hall, New York.

Farida A.A (2012). Dairy Microbiology. First edition. Random Publications. New Delhi, India.

Nduka Okafor (2007). Modern industrial microbiology and biotechnology. First edition. Science Publishers, New Hampshire, USA.

Roberts D and Greenwood M (2003). Practical Food Microbiology. Third edition. Blackwell publishing Inc, USA.

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