Microbiology Branches, History, and Careers


Microbiology is essential because microorganisms are everywhere, they surround us, and they live with us. Thus, it is expedient that a study of this branch of biology is created. Therefore, in order to understand and dissect the study of microorganisms known as microbiology, it is imperative that a general insight be given.

Table of Contents

What is microbiology?

Microbiology is a branch of biology that deals with the scientific study of microorganisms, primarily single celled organisms. It is derived from the Greek word micros “small” and bios “life”. In essence, microbiology is the study of small life forms that cannot be seen with naked eyes.

What are Microbes or Microorganisms?

Microbes are small, little and tiny living organisms found all around us. They inhabit all places or environments. For example, water, air, and soil. Fun fact, the human body is a host or home to millions of these microbes or microorganisms.

Most of these microbes are essential to our health and survival, as they play an important role in our lives. On the other hand, a handful of these microbes are agents of sickness and diseases. An example of a microorganism is a euglena.

Types of Microbes or Microorganisms

The common types of microbes are viruses, bacteria, and fungi. Although there are also other types like algae and protozoa that cause malaria and toxoplasmosis.


picture of fungi from a microscope in microbiology

Fungi are widespread microorganisms that possess the potential or ability to be both good and bad or harmful. Some species are healthy for humans and others are disease-causing microbes. The diseases caused by fungi are called mycoses and the most common fungal infection is the athlete’s foot.

Furthermore, fungi have been instrumental in the development of antibiotics since the discovery of penicillin. Some notable examples of fungi are; yeast, molds, and mushrooms which are edible.


Bacteria are single-celled microbes that respire anaerobically and aerobically, which means some of these microbes need oxygen and others do not. A majority of these bacteria live in or on our body, therefore aiding us in staying safe. Bacteria share similar features to eukaryotic cells such as a bacterial cell wall.

For example, the lactic acid bacteria found in the human bowels or the intestine help in the digestion of food. Some are needed in industrial capacities for the production of yogurt and cheese.

An exact number or figure cannot be stated of the disease-causing bacteria, but it is estimated that less than 1% of the total populace of bacteria are harmful. These bacteria cause tuberculosis, cold, and diarrhea. Some common examples of bacteria the salmonella and staphylococcus bacteria.

Gram Positive Bacteria

Gram positive bacteria are those examples of bacterial cells with a thicker peptidoglycan structure in their cell wall. In bacteriology, gram-positive bacteria can be defined as the bacteria that stain blue/purple, giving a positive result in a gram stain test.

These bacteria are different from the gram-negative bacteria that have a thin peptidoglycan cell wall and stain red to pink in the gram stain test. A gram stain test is a differential staining technique that is used to differentiate bacterial cells into gram-positive or gram-negative cells.


Viruses are microorganisms that do not have a cell on their own, but invade the host cell and use their DNA to multiply. They have molecules that are surrounded by protein in a shell that helps them to replicate or multiply once they invade a healthy cell.virus in microbiology

This equally means a virus cannot multiply on its own, unless or except through a living cell by invading it. Examples of viruses are the HIV virus, Measles virus, and COVID virus. And they cause diseases such as AIDS, measles, and flu or influenza. One type of virus is a bacteriophage.

We now have a brief and general understanding of microbes or microorganisms, further analysis of the subject topic (microbiology) can now commence.


A protist is a member of the kingdom Protista which includes all eukaryotic organisms that are not plantsanimals, or fungi. Protists are simple unicellular eukaryotic organisms though some can be found as a colony of cells or in multicellular form.

Brief History of Microbiology

Before the discovery of microbes, there have been hypotheses and predictions of their existence. Thus, during the 6th century BCE, the Janis postulated of their existence and several years later, the roman Marcus Terentius Varro also warned the people of locating their homestead in swampy areas.

This was because the creatures which they couldn’t see with their eyes could enter through the body (mouth and nose) and cause diseases. Furthermore, in the golden age of the Islamic civilization, Avicenna and Al-Razi hypothesized the existence of the microorganism in their books. Thus, in 1546, Girolamo Francastoro proposed the hypothesis that endemic diseases are caused by transferable seed-like structures. He also postulated that these structures can transmit infection by indirect or direct contact.

Hence, in 1665 Robert Hooke observed the fruiting bodies of molds and it is known as the first recorded observation of microbes. However, it is proposed that the Jesuit priest with the name Athanasius Kircher was the first to observe microorganisms through the development and help of his lenses. He started his investigation in1645 and published a book in 1658 titled Scrutinium Pestis (the examination of plague).

Furthermore, the development and use of the simple microscope by a man from the Netherlands called Antonie Van Leeuwenhoek opened the door to more microbial discoveries. His observation of bacteria and other microbes using his own design made him be considered and referred to as the father of microbiology.

During the 19th century, a floodgate of scientists came to the limelight with more discoveries and the classification of microbes. It started with the botanist Ferdinand Cohn, who worked on photosynthetic bacteria and algae. He was closely followed by Louis Pasteur and Robert Koch, who are known as the fathers of modern microbiology and medical microbiology respectively.

These scientists really made breakthroughs with food preservation known as pasteurization and the development of vaccines for diseases such as anthrax and rabies. Koch postulated a germ theory of disease and he further developed criteria known as the Koch’s Postulate and he was the first scientist to isolate bacteria in pure culture.

Other notable scientists in the field of microbiology are Martinus Beijerinck and Sergi Winogradsky. Beijernick was the first to discover and use the name virus to describe a microorganism and he also developed enrichment cultures used in the cultivation or growing of microbes.

Whereas Winogradsky was the first to discover the importance of microorganisms to the geochemical process. Through the concept of chemolithotrophy that was developed by him. And Joseph Lister was the earliest applied microbiologist, because of his effort in the use of phenol to disinfect open wound patients.

Branches of Microbiology

Microbiology is a branch of biology that has many sub-disciplines, as such, they are classified using two criteria namely; taxonomic microbiology and Applied Microbiology.

Taxonomic Microbiology

On this criterion, the branches are based on the name of the microorganisms. Therefore the branches are Bacteriology, Virology, Mycology, Microbial Ecology, Microbial Genetics, Protozoology, and cellular microbiology.


Bacteriology is the branch of microbiology that deals with the scientific study of bacteria. It’s morphology, ecology, genetics, and biochemistry.

Furthermore, it is also the study of bacteria and how it is related to medicine. Koch’s postulate (germ theory) has played a significant role in the identification of the relationships between bacteria and specific diseases. Since the formulation of such a postulate, the field of bacteriology has recorded increasing success and advancement that has led to the development of vaccines. For example tetanus toxoid and the development of antibiotics.

Since its postulation in the 19th century, the subfield of microbiology has made a great impact in public health and in the development of modern techniques for its precise study. The widespread knowledge of bacteria led to the use of vaccines as a tool in the prevention and treatment of diseases. The development of this field can be seen in the study of bacteria found in water (marine biology), biotechnology, agriculture, and pollution.

Significance of Bacteriology
  • Lactic acid bacteria (Lactobacillus and Lactococcus) have been recorded over the years to be a useful ingredient in the fermentation of foods. For example, yogurt, cheese, and pickle.
  • The ability of bacteria to degrade complex compounds has led to its application in waste management and processing, and bioremediation.
  • The study of bacteria has led to the production and use of eco-friendly pesticides.
  • This field has led to success in the understanding of genetics, biochemistry, and molecular biology. That is the understanding of metabolic pathways, production of enzymes, and expression of genes. The use of bacteria is done in order to understand an entire organism through the production of mathematical models.


Virology is the branch of microbiology that is concerned with the scientific study of virus and virus-like agents. Its major focus is on the structural aspect, classification, evolution, infectious ways, and host cell exploitation for reproduction. Furthermore, the diseases they cause through the interaction with the host physiology and immunity.

In addition, the techniques and methods used in isolating and culturing them are studied in this field.

Since its discovery in 1898 by Martinus Beihernick, the field of virology has seen great advancements as technology advances alongside.

Virus Structure and Classification

Classification is based on the host cell they impact, the geometrical shape of their capsid, virus structure, and type of nucleic acid.

Host cell they impact
Geometrical Shape of capsid
Structure of virus
Type of nucleic acid
Animal viruses
Helix viruses
Presence of lipid envelope viruses
DNA viruses
plant viruses,
icosahedrons viruses
absence of lipid envelope viruses
RNA viruses
fungal viruses,
sizes range from 30nm-450nm viruses.
Reverse transcribing viruses
Virus-like agents

These are sub-viral particles that are infectious and smaller than viruses. These particles or entities include;

  • Viroids (Naked circular RNA molecules that affect plants)
  • Satellites (These are particles that require a helper virus for infection and reproduction)
  • Prions (these are pathogenic proteins that conform to other prion molecules)
Viral Diseases and Host Defenses

The ability of viruses and virus-like particles in causing disease has motivated virologists to study more. A study on how the disease is caused, how it can be managed or even stop them from replicating.

Some examples of the diseases caused by viruses and virus-like particles are AIDS, common cold, rabies, measles, herpes, hepatitis, and yellow fever. Therefore, in defense to the virus, the host either plant or animal exhibits some immune character or response that aids in its quest to fight and destroy the virus and virus-like particles.

Vertebrates produce antibodies when the virus comes in contact with the immune system. These antibodies attach themselves to the virus and neutralize or mark them for destruction. The uses of vaccines are also used to help the antibodies fight against viruses.

Furthermore, T-cells, which are cell-mediated immunity also helps to target cells with viral fragments and destroys them. In addition, RNA interference helps to destroy single-stranded infected RNA of plants and animals.


Mycology is the branch of microbiology that deals with the scientific study of the genetic, biochemical properties, taxonomic, uses, toxicity, and infection of fungi. Therefore, due to the fact that most plant diseases are fungal in nature, it is therefore closely related to Phytopathology.

Fungi are manufacturers of toxins, antibiotics, and secondary metabolites. For instance, the genus Fusarium are known for their toxin production that is associated with fatal outbreaks of alimentary toxic aleukia in humans.

Also, their role as symbionts is a fundamental aspect of life as they break down complex organic biomolecules such as lignin and pollutants like petroleum and polycyclic aromatic hydrocarbons. By the decomposition of these molecules, it is thus said that fungi play an important role in the global carbon cycle.

Hence, because of their ability to cause diseases, both in plants and animals, it should be noted that they possess social and economic importance. In plants, they cause diseases such as rice blast and in animals, they cause histoplasmosis.

Another point about this field is that the study of the important benefits of fungi as many species helps in the control of plant diseases caused by many pathogens. For instance, the genus Trichoderma is considered to be an important biological control agent. Furthermore, the field of mycology has aided in the discoveries of drugs that have helped humans and it will continue to help. Such drugs include;

  • Penicillin
  • Cephalosporin
  • Ciclosporin
  • Psilocybin
  • Gristeoflulvin
  • Vitamin D (from mushroom)


Phycology is the branch of microbiology that deals with the scientific study of algae. As it is known, algae are important primary producers in aquatic ecosystems.  This branch also studies microscopic algae and their nature as symbionts and how they exist in prokaryotic forms such as cyanobacteria or blue-green algae.

Also, many of the algae are single-cell microscopic organisms that live in wet environments. In addition, a study of freshwater or ocean algae and diatoms or soft algae are also considered.


Protozoology is concerned with the study of protozoa, major members of this category are amoeba and Plasmodium.

Microbial Genetics

Microbial Genetics is the branch of microbiology that is a combination of microbiology and genetic engineering. This field helps with the evolution theory proposed by Charles Darwin, especially the theory of natural selection. Furthermore, this field deals with genotype studies and expression systems of microbes.

As it is known, that some viruses are categorized based on nucleic acid, it is, therefore, paramount that a field is created that studies these microbes and how they can be engineered genetically to aid in the understanding of biological science.

Microbial Ecology

Microbial Ecology is the branch of microbiology deals with the study of the relationship between microbes and with their environment. And because of their omnipresence nature in the biosphere, they impact or affect the biosphere in every direction.

They play a primary and major role in the regulation of the biogeochemical systems of our environment. This is possible because they can be found everywhere in our environment from the coldest to the hottest environment. They also aid the environment in the global biogeochemical cycles, they are carbon reserves and also present in the fixing of carbon and aid in metabolic processes.

Roles of microbes in the environment
  • They are the backbone of every ecosystem when it comes to the provision of energy through chemosynthesis to plants that cannot photosynthesize direct sunlight energy.
  • They are decomposers with the ability to recycle nutrients from waste products and other organisms. The microbes that are responsible for this process play an important role in the biogeochemical cycles. For example, the nitrogen, phosphorus, sulfur, and carbon cycle.
  • They play another important role in the study of evolution due to their high level of horizontal gene transfer.
Symbiosis in Microbial Ecology

Microorganism especially bacteria are often involved in a symbiotic relationship (which is either positive or negative) with other or bigger organisms. The types of symbiotic relationships that occur in microbes include; mutualism, commensalism, and amensalism.


In microbial ecology, this is the relationship between microbial species and humans that gives room for both sides to benefit. An example is the syntrophy relationship between an ethanol fermenting microorganism and a methanogen.


In the microbial world, this is a relationship where both parties, neither benefit nor loses from their interaction. It is a relationship where metabolic products of one microbial population are used without gain or harm by another microbial population. For instance, the microbial population (methanogens) produces methane by reducing CO2 to CH4, whereas another microbial population (methanotrophs) oxidizes methane back to CO2.


This is a microbial relationship between two microorganism populace that makes one population suffers loss or harm and the other population is unaffected. For example, the relationship between the microbial population of Lactobacillus casei and Pseudomonas taetrolens. These populations co-exist in an environment, hence the by-product of lactobacillus casei produce during its production of lactic acid affects the population of pseudomonas taetrolens by inhibiting their growth and decreasing the production of their main product called lactobionic acid.

Applied Microbiology

On this criterion, we have sub-divisions of branches such as food microbiology, industrial microbiology, and medical microbiology.

Industrial Microbiology

This is a branch of microbiology that applies microbial knowledge in the mass production of industrial products, This is achieved through the manipulation of microorganisms to increase yields. Thus three major applications of microorganisms in the industry will be discussed subsequently.

Medical Application

The medical application concerned with industrial microbiology is used primarily in the production of new drugs. This is achieved through the synthesis of specific microorganisms for medical purposes. Formicroscope for microbiology example, the production of antibiotics for the treatment of bacterial infection is achieved through this method.

Through the process of fermentation, an ideal environment is provided for the microorganism to grow and produce the antibiotic before its being extracted. Also, biotransformation is another process of using microbes to transform a product from one chemical composition to another.

Like in the case of the mass production of vitamin B12 (riboflavin) where the microorganism (Eremothecium ashbyii) is used to transform glucose to riboflavin before extraction. Biotransformation is also used in the production of steroids. For instance, with the aid of Corynebacterium species dehydroepiandrosterone, is transformed into a steroid (testosterone).

Food Industry Application

The food industry cannot be dissected without mentioning fermentation as a process that involves the use of microbes to increase the yields of food products, therefore, fermentation is the process whereby sugar is broken down and converted into gas, acids, and alcohol.

Also, the process is anaerobic which means that it takes place without oxygen. Yeast and bacteria are the commonly used microbes for fermentation. For example, products like alcohol and ethanol are products of fermentation. In addition, dairy products like cheese and yogurt are produced by fermentation using microorganisms.

Enzymes are also produced either by submerged or solid-state fermentation.

Agriculture Application

The increasing need for fertilizers and pesticides is on the rise to meet the growing demand for the consumption of agricultural products. Hence the need to use a more efficient way to meet the high demand. Therefore, the need for biofertilizers and biopesticides to meet up with the demand because chemical processes leave a dent in the environment.

Bacillus thuringenesis is a microorganism used as a biopesticide to control the pest population. Thus biopesticides is the use of living organism or naturally occurring substances to mitigate pest infestation. Again microbes are used to synthesize amino acids and organic solvents which are used as food and pharmaceutical products.

Food Microbiology

This is a sub-category of microbiology that deals with microbes that create, inhibit, or contaminate food, and pathogens that cause food spoilage hence causing disease. Microorganisms used in the fermentation of food products and the useful roles of microbes in the production of probiotics are embedded in this field of microbiology.

 A Sub-group of bacteria that impact food
Impact on food
Lactic acid bacteria (streptococcus thermophilia)
Produces lactic acid by acting on carboghydrates
Acetic acid bacteria (Acetobacter aceti)
Produces acetic acid
Propioni bacterium freudenreichii
Produces propionic acid
Clostridium butyricum
Produces butyric acid
Proleotytic bacteria (staphylococcus)
Produces extracellulant proteinase
Lipolytic bacteria (micrococcus)
Produces extracelluar lipase

Medical Microbiology

This is the branch of microbiology that is concerned with the study of microorganisms and their ability to cause diseases. It also studies the prevention, diagnosing, and treatment of diseases. It also deals with how microbes can be clinically developed and applied to improve human health.

The major microbes causing infectious diseases fall under bacteria, viruses, fungi, and parasites. In addition, the characteristics of the pathogen, their mode of transmission, mechanism of infection, and growth are also studied.

Commonly Treated Infectious Diseases
  • Streptococcal pharyngitis
  • Tuberculosis
  • Typhoid fever
  • Chlamydia
  • Dandruff
  • Candida
  • Histoplasmosis
  • Malaria
  • Giardia lambia
  • Toxoplasma gondi
Causes and transmission of microbial infectious diseases

The four main classes of microbes are generally the major causes of infectious diseases. Also, they are endogenous (from a normal plant) or exogenous (from an external source). Thus, they are many ways they infect their host through the portal of entry. Therefore, some of the ways of infection include;

  • Indirect contact
  • Direct contact
  • Droplet contact
  • Fecal-oral route
  • Environmental
  • Vector transmission
  • Airborne transmission
  • Fomite transmission
Diagnostic test of microbial infections

It is important to diagnose the disease or infection, in order to receive the appropriate treatment. Therefore, there are some tests that can be conducted to determine the causative agent and they are as follows;

  • Microbial culture (solid culture, liquid culture, or cell culture)
  • Microscopy
  • Biochemical tests
  • Genotyping
  • PET scan
  • X-rays
Treatment of microbial infections

After diagnosing the disease, the proper treatment plan is recommended based on the strand of the microbe. Meaning that if it is a bacterial, viral, or fungal infection, thus, the recommended drugs will be anti-bacterial, anti-viral, or anti-fungal.

Careers in Microbiology

You can make a great career in microbiology and help shape the future. They are several fields that you can specialize in. It could be a field in taxonomic microbiology or applied microbiology. And also a great salary structure per annum. Jobs in microbiology are all over because of the ever-present nature of microbes in our lives. So a degree in this course will definitely be a major boost to your academic quest.


Are microbiology and molecular biology the same?

Microbiology and molecular biology are similar branches of Biology. Molecular Biology aims to understand living organisms by examining the structure and functions of molecular components that construct them. Microbiology is the branch of biology which deals with the study of microorganisms.

What is the difference between microbiology and biology?

The difference between microbiology and biology is that Biology deals with both the macroscopic and microscopic organisms. Microbiology deals only with microscopic organisms.

What microbiology is all about?

Microbiology is the study of the biology of microscopic organisms. These include viruses, bacteria, algae, fungi, slime molds, and protozoa. The methods used to study and manipulate these minute and mostly unicellular organisms differ from those used in most other biological investigations.

What are the benefits of studying microbiology?

The benefits of studying Microbiology are that it helps us to identify the microorganisms that exist in food. With a better understanding of these microorganisms, help the biologists to find out the ways for preventing the food from spoilage and make food safe. Scientists use good bacteria against pathogenic bacteria to prevent food contamination.

Which microbiology section studies fungi?

In addition to the well-known macroscopic fungi (such as mushrooms and molds), many unicellular yeasts and spores of macroscopic fungi are microscopic. For this reason, fungi are included within the field of microbiology. Fungi are important to humans in a variety of ways.