Microbiology is the branch of science that deals with
microorganisms. Microorganisms are small living things that include
unicellular, multicellular, or acellular. Unicellular are single cells
organisms like cocci, bacilli, virio, and spirillae (Fig.1). Multicellular are
filaments and sheaths to form cell colonies like blue-green algae
(cyanobacteria), fungi, protozoans, and bacteria (Fig.2). In contrast, acellular is
organism without cells, like viruses, prions (Fig.3). These microorganisms are
not visible by naked eyes, only observed under microscope. Like other
organisms, microorganisms survive, grow, and also require a source of energy
and nourishment to survive and grow. Many microorganisms are beneficial to
humans and some are pathogenic in nature.
Fig. 1: Unicellular single-cell organisms
Fig. 3: Acellular Organisms
Branches of Microbiology
General microbiology is classified into three main branches
which are tabulated below.
By Taxonomy
• Bacteriology: It is the study of bacteria.
• Immunology: It is the study of the immune system.
It looks at the relationships between pathogens such as bacteria and viruses
and their hosts.
• Mycology: It is the study of fungi, such as yeasts
and molds.
• Nematology: It is the study of nematodes
(roundworms).
• Parasitology: It is the study of parasites. Not all
parasites are microorganisms, but many are. Protozoa and bacteria can be
parasitic; the study of bacterial parasites is usually categorized as part of
bacteriology.
• Phycology: It is the study of algae.
• Protozoology: It is the study of protozoa,
single-celled organisms like amoebae.
• Virology: It is the study of viruses.
By Type of Research
• Astromicrobiology: It is the study of the origin of
life on Earth, and the search for extraterrestrial life. • Evolutionary
microbiology: It is the evolution of microorganisms.
• Microbial cytology: It is the study of microscopic
and submicroscopic details of microorganisms.
• Microbial physiology: It is the study of the biochemical
functioning of microbial cells with respect to the study of microbial growth,
microbial metabolism, and microbial cell structure.
• Microbial ecology: It is the relationship between
microorganisms and their environment.
• Microbial genetics: It is the study of how genes
are organized and regulated in microbes in relation to their cellular functions
which is closely related to the field of molecular biology.
• Cellular microbiology: It is a discipline bridging
microbiology and cell biology.
• Evolutionary microbiology: It is the study of the
evolution of microbes. This field can be subdivided into:
Microbial taxonomy: It is the study of the naming and
classification of microorganisms.
Microbial systematics: It is the study of the
diversity and genetic relationship of microorganisms.
• Generation microbiology: It is the study of those
microorganisms that have the same characteristics as their parents.
• Molecular microbiology: It is the study of the
molecular principles of the physiological processes in microorganisms.
• Nano microbiology: It is the study of those
microorganisms on the Nano level.
• Biological agent: It is the study of those
microorganisms that are being used in weapon industries.
Applied Microbiology
• Medical microbiology: It is the study of the
pathogenic microbes that are responsible for human illness. It includes the
study of microbial pathogenesis and epidemiology and is related to the study of
disease pathology and immunology.
• Pharmaceutical microbiology: It is the study of
microorganisms that are related to the production of antibiotics, enzymes,
vitamins, vaccines, and other pharmaceutical products and that cause
pharmaceutical contamination and spoil.
• Industrial microbiology: It is the exploitation of
microbes for use in industrial processes like industrial fermentation and wastewater
treatment which is linked to the biotechnology industry.
• Microbial biotechnology: It is the study of genetic
and molecular level manipulation of microorganisms to generate useful products.
• Food microbiology and Dairy microbiology: It is the
study of microorganisms causing food spoilage and food-borne illness.
• Agricultural microbiology: It is the study of
agriculturally relevant microorganisms. This field can be further classified
into the following: Plant microbiology and Plant pathology, where the
interactions between microorganisms and plants and plant pathogens are studied.
Secondly soil microbiology: It is the study of those microorganisms that are
found in soil.
• Veterinary microbiology: It is the study of the
role of microbes in veterinary medicine or animal taxonomy.
• Environmental microbiology: It is the study of the
function and diversity of microbes in their natural environments. This involves
the characterization of key bacterial habitats such as the rhizosphere and
phyllosphere, soil and groundwater ecosystems, open oceans, or extreme
environments (extremophiles). This field includes other branches of
microbiology such as:
Microbial ecology: It is the study of the
relationship of microorganisms with one another in their environment.
Microbially mediated nutrient cycling: It is the
study of the movement and exchange of organic and inorganic matter back into
the production of matter through microorganisms.
Geomicrobiology: It is the interdisciplinary study of
the interactions of microorganisms and earth materials such as soil, sediment,
atmosphere, minerals, and rocks.
Microbial diversity: It is the study of the number of
species and abundance of each species of microorganisms that are distributed in
an ecological community.
Bioremediation: It is a process used to treat
contaminated media, including water, soil, and subsurface material, by altering
environmental conditions to stimulate the growth of microorganisms and degrade
the target pollutants.
Aquatic microbiology: It is the study of those
microorganisms that are found in water.
Aero microbiology: It is the study of airborne microorganisms.