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.
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]
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.
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]
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 |
|---|---|---|---|
|
1 |
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. |
|
2 |
Peptidoglycan layer |
It’s thick and can be present in multilayers. |
It’s thin and only present in a single layer. |
|
3 |
Outer membrane |
Absent |
Mostly present |
|
4 |
Morphology |
Cocci or spore-forming bacilli. |
Non-spore forming bacilli. |
|
5 |
Lipid content and lipopolysaccharide |
They have low lipid content, and lipopolysaccharide is absent. |
They have 20-30% lipid content, and lipopolysaccharide is present. |
|
6 |
Resistance to antibiotics |
They are more susceptible to antibiotics. |
They are more resistant to antibiotics |
|
7 |
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. |
|
8 |
Examples |
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]
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]
Fungi share some characteristics with other eukaryotes, plants, and animals; these include:[9]
Most fungal species cause disease in plants and animals, but some also have practical applications in different areas, for example:
Figure: An image of two different varieties of mushrooms (a) Polyporus squamosus and (b) Armillaria ostoyae[9]
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]
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]
Some practical benefits of algae in human life include:[11]
Figure: Microscopic images of different types of freshwater algae.[11]
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 |
|---|---|---|
|
1 |
Amoebiasis |
Entamoeba histolytica |
|
2 |
Trichomoniasis |
Trichomonas vaginalis |
|
3 |
African sleeping sickness |
Trypanosoma brucei |
|
4 |
Leishmaniasis |
Leishmania spp. |
|
5 |
Malaria |
Plasmodium spp. |
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.
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]
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.
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