What is Microbiology? 

Microbiology is the study of microbes/microorganisms: minute naked organisms to human eyes, including bacteria, protozoa, archaea, fungi, and viruses.

There are pros and cons to everything we know, and the same applies to these microorganisms; some microbes are deadly to the planet’s health while others help keep this planet healthy. 

For example, studying microbes is essential in the medical sector to understand how these tiny organisms cause diseases and their diagnosis and cure. Further, understanding these organisms also led to discovering their uses for human health as nutrition or medicine and curating innovative agricultural products.

This article sums up everything on microbiology, its relevant branches, the study of microbes it involves, and the importance of microbiology in our lives.

Branches of Microbiology

Microbiologists study microbes at an array of levels, including molecular level (gene and proteins), cellular level (cell and physiology), and community level (ecology, epidemiology, and public health).[1]

For the easy study of microbes —that might be present in infinite numbers— and due to the importance of microbiology, the subject is divided into several branches like mycology, parasitology, virology, bacteriology, and microbial genetics.[1]

  1. Mycology: It is concerned with studying fungi, ranging from their taxonomy, molecular studies, genetic studies to biochemical properties. It also addresses their applications in human life as a source for tinder, food, entheogens, and traditional medicine, as well as their potential hazards such as toxicity and infection.[2]
  2. Parasitology: It is the study of parasites, parasitic diseases, their biology, including their distribution, physiology, biochemistry, ecology, evolution, molecular biology, and clinical aspects, as well as their responses to their hosts.[3]
  3. Virology: It’s the study of viruses and virus-like agents. It includes the findings on their taxonomy, evolution, disease-producing properties, cultivation, genetics, and their application in research and therapy.[4]
  4. Bacteriology: It’s a branch of microbiology that deals with the study of bacteria. It specifically includes the study of bacterial morphology, ecology, genetics, and biochemistry.[5]
  5. Microbial genetics: In the study of microbial genetics, we explore the mechanisms involved with the transmission of heritable information in microorganisms such as bacteria, archaea, viruses and protozoa, and fungi.[6]

Types of Microorganisms

Microbiology involves the study of diverse microbial populations, including viruses, bacteria, fungi, algae, protozoa, lichens, and slime molds. Have a look at some of these in detail.

1. Bacteria

Bacteria are ubiquitous and one of the first life forms on earth. They are present in diverse habitats, from the soil, underwater, Earth crust depth, to extreme conditions like acidic hot springs and radioactive waste.[7] Also, they are profoundly available in lakes and oceans, in arctic ice, and geothermal springs.

Bacteria are generally free-living, unicellular, and microscopic (a few micrometers in length) organisms. They have a wide range of sizes and shapes. Most of them are rod-shaped (called bacilli) or spherical shaped (called cocci) and vary in sizes ranging from 0.5 to 5.0 micrometers in length.[7]

various shapes of bacteria

Figure: An illustration of various shapes of bacteria discovered so far.[7]

From the outer environment, bacterial cells are surrounded by a cell wall, with a plasma membrane on the inside that mainly consists of phospholipids.

The bacterial cell wall is composed of peptidoglycan, formed by polysaccharide chains cross-linked by D-amino acids containing peptides. Furthermore, bacteria are classified into two groups based on the thickness of their peptidoglycan layer: Gram-positive bacteria and gram-negative bacteria.[7]

The differences between these two bacteria are explained in the table below:[8]

S. No. Characteristics Gram-positive bacteria Gram-negative bacteria
Cell wall
They have a single-layered smooth cell wall thickness of 20 - 80 nm.
They have a double-layered, wavy cell wall thickness of 8 - 10 nm.
Peptidoglycan layer
It's thick and can be present in multilayers.
It's thin and only present in a single layer.
Outer membrane
Mostly present
Cocci or spore-forming bacilli.
Non-spore forming bacilli.
Lipid content and lipopolysaccharide
They have low lipid content, and lipopolysaccharide is absent.
They have 20-30% lipid content, and lipopolysaccharide is present.
Resistance to antibiotics
They are more susceptible to antibiotics.
They are more resistant to antibiotics
Gram staining
After gram staining, they appear purple under a microscope.
After gram staining, they do not retain the stain and appear pink under the microscope.
Staphylococcus and Streptococcus
Escherichia and Salmonella

Unlike eukaryotes, they don’t contain membrane-bound organelles like mitochondria, chloroplast, and nucleus.[7] Their genetic material is stored in an irregularly-shaped body, called a nucleoid, in the form of a single circular chromosome (called a plasmid). The chromosome in the nucleoid is also associated with proteins and RNA, and they reproduce or multiply by a type of asexual reproduction called binary fission.

Their species have different interactions with other organisms – it can be mutualistic, commensalism, predator relation, or pathogenic. It depends on the bacterial species.[7]

An extensive range of bacterial colonies that can be enumerated also contributes positively to human needs. Some of its applications are:[7]

  • Bacteria such as Lactobacillus used to prepare fermented foods like cheese, yogurt, soy sauce, and wine combined with yeasts and molds.
  • Some species of bacteria that can digest hydrocarbons in petroleum are used to clean the oil spill.
  • They are used for the bioremediation of industrial toxic wastes.
  • Some species of bacteria are bioengineered to produce therapeutic proteins such as insulin, growth factors, or antibodies.

2. Fungi

Fungi are complex multicellular eukaryotes (except yeast, which is unicellular or single-celled) that include microorganisms like yeasts, molds, and mushrooms.[9] They primarily inhabit the land, soil, or plant material. Some are found in extreme environments like deserts, areas with high salt concentrations or high ionization radiation, and deep-sea sediments.[9]

Morphologically, fungi have a thread-like structure called hyphae. They give rise to many other structures by branching and fusing into a structure called mycelium.

Taxonomists have described around 148,000 fungi species as of 2020.[9] And they can be classified in different ways, such as size, shape, fruiting bodies, and biochemical and physiological characteristics.

They are classified into the following groups based on their life cycle, presence of the fruiting body, and spores arrangement and types they produce:[10]

  • Multicellular filamentous molds
  • Macroscopic filamentous fungi with large fruiting bodies.
  • Single-celled microscopic yeasts

Fungi share some characteristics with other eukaryotes, plants, and animals; these include:[9]

  • Characteristics similar to plants: Fungi have a cell wall and vacuole similar to plants, and like moss and ferns, they also produce spores. Furthermore, they can also reproduce by both sexual and asexual means.
  • Characteristics similar to animals: Animals and fungi both lack chloroplasts and are heterotrophic, thus requiring organic compounds as an energy source.
  • Characteristic similar to other eukaryotes: Fungi, like other eukaryotes, possess membrane-bound nuclei (containing genetic material) and other organelles, such as mitochondria. Furthermore, they have an extensive range of soluble carbohydrates and storage compounds, like sugar alcohols and polysaccharides.[9]

Most fungal species cause disease in plants and animals, but some also have practical applications in different areas, for example:

  • Fungi are used in food processing, preparation, and preservation. They are also used for the fermentation of food items; for example, Saccharomyces cerevisiae, also known as Baker’s yeast, is used to make bread and other wheat-based products.[9]
  • Some fungal species have applications in modern chemotherapeutics and traditional medicines. For example, penicillin G is an antibiotic obtained from Penicillium chrysogenum; griseofulvin is isolated from Penicillium griseofulvum (used to treat fungal infections) polysaccharide-K compound isolated from Trametes versicolor is used as an adjuvant for cancer therapy in Europe and Japan.[9]
  • Some fungi, like white-rot fungi, work well in the bioremediation processes.

Figure: An image of two different varieties of mushrooms (a) Polyporus squamosus and (b) Armillaria ostoyae[9]

3. Algae

Algae is a large group of predominantly aquatic photosynthetic organisms. They range from unicellular microalgae, like chlorella and diatoms, to multicellular algae, such as giant kelp and brown algae.[11] Most algae are autotrophic like plants but lack many significant cells and tissues present in plants, such as stomata, xylem, and phloem.

Algae are classified in several ways based on a variant of characteristics. And depending on the pigments they contain, algae are classified into three groups:[11]

  • Green algae (Chlorophytes)
  • Red algae (Rhodophytes)
  • Brown algae (Phaeophytes)

Some algal species live in symbiotic relationships with other organisms. The host derives its nutritional requirements from algae and provides them protection in return. Some of them are:[11]

  • Lichens: It is a complex life form formed by two organisms, a fungus, and algae, symbiotically linked together. Here, fungi are the dominant partners that impart more physical characteristics to lichens, and algae predominantly associated with forming lichens are either green algae or blue-green algae. A few examples of lichens are Graphis scripta and Ochrolechia parella, and macrolichen.[12]
  • Coral Reefs: They are large underwater structures made up of the skeletons of colonial marine invertebrates called coral. Some of the corals build reefs by extracting calcium carbonate from seawater. They are called hard corals.[13] They often harbor dinoflagellates algae in their cells, which help them live healthy.
  • Sea Sponges: A few species of algae live on the surface of sponges, where they provide sugar and oxygen for their growth and get protection from predators in return.

Some practical benefits of algae in human life include:[11]

  • Algae are used to derive agar used in food and labs to grow plants and microorganisms.
  • Alginate extracted from brown algae is used in some food and medical dressing.
  • Some algae species are used as fertilizers, soil conditioners, and livestock feed.
  • Chlorella and Spirulina are used in some countries as nutritional food items.[11]

Figure: Microscopic images of different types of freshwater algae.[11]

4. Protozoa

Protozoans are single-celled eukaryotic organisms living in a wide range of habitats, from freshwater, marine environments to the soil. Most of them are parasitic that live in plants or animals, and cause severe diseases.[14] They can reproduce by both sexual or asexual means. They lack a cell wall and possess flagella and cilia that help them move in the water. 

Some of the diseases caused by protozoans are:[14]

No. Disease Causative Protozoa
Entamoeba histolytica
Trichomonas vaginalis
African sleeping sickness
Trypanosoma brucei
Leishmania spp.
Plasmodium spp.
microscopic images of different protozoan species

Figure: microscopic images of different protozoan species.[14]

Picture By: Frank Fox, Sergey Karpov, CDC/Dr Stan Erlandsen, Picturepest, Thierry Arnet, and Dr Tsukii Yuuji.

5. Viruses

Viruses are infectious agents that are submicroscopic and can only survive in living organisms. The first virus, the tobacco mosaic virus, was discovered in 1898 by Martinus Beijerinck. And since then, around 9000 species of viruses have been found and studied by scientists.[15]

Viruses are much smaller than bacteria and possess a broad range of shapes and sizes. However, the five predominant shapes of viruses are helical, icosahedral, prolate, enveloped, and complex.[15]

Figure: A representation of different viruses and their shapes and sizes.[15]

Viruses have either DNA or RNA (mostly) as genetic material, unlike other organisms that only contain DNA as their genetic material. Different viruses can either have single-stranded RNA, double-stranded RNA, single-stranded DNA, or double-stranded DNA forms.[15]

Viruses are acellular organisms that require the machinery of their host cell to produce and multiply in hundreds or thousands. They cause several diseases in humans, animals, birds, bacteria, and even archaea.[15]

What is the Importance of Microbiology?

Microorganisms contribute to the world in myriads of ways. Apart from some that cause harm, there are others who have immense importance[16] in our ecosystem and health system. Some of these benefits are explained below.
  • Agriculture: Microbes help plants take required nutrients by breaking down complex compounds into simpler forms. They also make the soil rich in nutrients and minerals (like nitrates) that enhance crop yield.[16] Microbes help plants fix nitrogen, and some of them are used as biofertilizers, thus contributing to a better and higher output.
  • Biotechnology and genetic engineering: Microbial studies have allowed scientists to understand their working mechanisms and engineer them in a way that helps in the increased production of medicinal compounds.It is believed that the insertion of foreign genes in some bacterial species might lead to creating a bacterial strain that can provide solutions to myriads of challenges, including pollution, food and energy shortages, and the treatment and control of the disease.[16]
  • Producing certain compounds: Bacteria are used in industries to make new products from the provided raw materials. They can perform a metabolic reaction rapidly on a large scale that meets the population’s demand for medicines, food materials, or other chemical compounds, such as insulin and other growth hormones.
  • Combating diseases: The study of microbes has unraveled their potential in treating several deadly conditions. For example, several bacterial species are used to isolate medicinal compounds, like antibiotics and develop vaccines.[16]
  • Keep the planet healthy: Microbes play an essential role in recycling minerals like nitrogen and carbon for easy availability to other organisms, keeping the environment oxygenated, and actively degrading organic matter.
  • Food processing: The study of microbiology has enlightened us on the application of microbes as an essential source of nutrients. For example, some algal and fungal species are part of people’s meal, such as mushroom, Chlorella, Spirulina, and certain microbes are also used in food processing, fermentation, baking, and producing livestock feed.


Microbiology is the study of microbes’ diversity, ranging from taxonomy, evolution, morphology, metabolic processes, molecular mechanisms, genetic material, mechanism of disease causation, response with host, and the importance of microbiology in creating a better and healthier planet.

The subject talks about all microbes, including bacteria, viruses, fungi, algae, protozoa, slime molds, lichens, and many more. A better understanding of these organisms has a significant role in the medical sector. By utilizing the knowledge, one can better understand disease causative agents and possible diagnoses and treatment approaches.

It’s a field full of opportunities where young scientists can get the chance to unravel the potential of these microbes for the benefit of human health and the environment. Researchers are currently digging deep into some microbial species for their role in combating pollution problems, creating better treatment options, producing medicines, enhancing crop production, and producing nutrient-rich food.


  1. What Is Microbiology and Why Is It Important? Retrieved from https://www.srgtalent.com/career-advice/roles-in-focus/microbiology
  2. Mycology. Retrieved from https://en.wikipedia.org/wiki/Mycology
  3. Parasitology. Retrieved from https://www.nature.com/subjects/parasitology
  4. What is Virology? Retrieved from https://www.news-medical.net/health/What-is-Virology.aspx
  5. Bacteriology. Retrieved from https://www.britannica.com/science/bacteriology
  6. Microbial genetics. Retrieved from https://www.nature.com/subjects/microbial-genetics
  7. Bacteria. Retrieved from https://en.wikipedia.org/wiki/Bacteria
  8. Difference between Gram-Positive and Gram-Negative Bacteria. Retrieved from https://byjus.com/biology/difference-between-gram-positive-and-gram-negative-bacteria/
  9. Fungus. Retrieved from https://en.wikipedia.org/wiki/Fungus
  10. Fungi. Retrieved from https://microbiologysociety.org/why-microbiology-matters/what-is-microbiology/fungi.html
  11. Algae. Retrieved from https://en.wikipedia.org/wiki/Algae
  12. Lichen. Retrieved from https://en.wikipedia.org/wiki/Lichen
  13. Coral reef. Retrieved from https://en.wikipedia.org/wiki/Coral_reef
  14. Protozoa. Retrieved from https://en.wikipedia.org/wiki/Protozoa
  15. Virus. Retrieved from https://en.wikipedia.org/wiki/Virus
  16. Why is Microbiology Important? Retrieved from https://www.labmate-online.com/news/news-and-views/5/breaking-news/why-is-microbiology-important/35152