Are Viruses Microorganisms?

 

Christine Somerjin commented on 

https://scientificlogic.blogspot.com/2020/05/viruses-are-very-intolerant-to-high.html

She asked: “I have always wondered if viruses are microorganisms like bacteria or something else. Maybe you can tell us”

Thank you for your question Somerjin

Your question touches on an interesting aspect of microbiology and the debate surrounding the nature of viruses.

Viruses are indeed a unique case in the study of microorganisms. They differ significantly from bacteria, fungi, and parasites in several ways, particularly in their classification as non-living entities when outside a host cell.

In order to answer your question, we will need to first explain what are microorganisms and their characteristics?  

There are only 3 types of microorganisms we know.

 First on the list most people know are the bacteria. These are single-celled, living organisms that can reproduce independently through binary fission. They have a cellular structure with a cell membrane, cytoplasm, and DNA. Bacteria can metabolize nutrients, grow, and respond to their environment.

Second on this list are the micro fungi less know by most people.  This group includes yeasts and moulds, which are also living organisms. They have more complex cellular structures than bacteria and reproduce via spores. They are capable of metabolism, growth, and environmental response.

Even less recognised are the microparasites.  These include protozoa and certain microscopic worms that are also living organisms. They have cellular structures, can reproduce, and carry out metabolic processes. An example in Malaysia and in tropical countries is the malarial parasites that causes malaria, and the microfilaria, an early stage in the life cycle of parasitic nematodes in the family Onchocercidae. This microparasite causes lymphatic filariasis, commonly known as elephantiasis that is a painful and profoundly disfiguring disease over the legs. It is caused by infection with parasites classified as nematodes (roundworms) of the family Filariodidea that are transmitted through the bites of infected mosquitos

But for your question, viruses are a special case much debated if they can be classified as a microorganism. In order to answer, we need to look at the structure of viruses.  Viruses are composed of genetic material (either DNA or RNA) enclosed in a protein coat, sometimes with an additional lipid envelope. They lack the cellular machinery necessary for metabolism and reproduction.

The life cycle is also different.  Viruses cannot reproduce independently. They require a host cell to replicate, hijacking the host's cellular machinery to produce new viral particles. Outside a host, viruses are inert and do not exhibit the characteristics typically associated with life, such as metabolism or growth. Because of their dependence on a host for reproduction and their lack of cellular structure, viruses are often considered on the borderline between living and non-living. They do not meet the traditional criteria for life, such as metabolism and independent reproduction, which is why they are not classified as living microorganisms like bacteria, fungi, or parasites.

While bacteria, micro-fungi, and microparasites are considered microorganisms because they are living, viruses are generally not classified as microorganisms in the traditional sense because they are not living outside a host. However, they are studied within microbiology due to their relevance in disease and interaction with living cells. For practical purposes, viruses are often included in discussions of microorganisms because they are microscopic and have significant biological impacts.

We can say viruses occupy a unique position in biology. They are not considered living organisms and, therefore, differ from bacteria, fungi, and microparasites. However, due to their microscopic size and importance in health and disease, they are often included in the study of microorganisms, even though they are not alive by traditional definitions.

To sum up. The study of microbiology includes:

1.      Bacteriology

2.      Mycology 

3.      Parasitology 

4.      Virology? 

I hope this clears up the distinction!