Table of Contents
Introduction
Microbiology is a branch of science that deals with the study of diverse groups of microorganisms that include bacteria, fungi, algae and protozoa. It also includes viruses and acellular components that are sometimes considered non-living. The study of microbiology deals with the nutrition and functioning of microorganisms as well as their effect on plants and animals.
Microbiology has been derived from Greek words micros (small), bios (life) and logos (science). The name microbiology indicates that it includes microorganisms that cannot be seen with the naked eye. However there are some microbes that can be seen with naked eyes such as filamentous algae, bread moulds, mushrooms, and some bacterias.
Microbiology talks about how microbial life affects other microbes as well as non-microbial life. It encompasses the activities of microorganisms that are both beneficial and harmful to soil, water, plants, humans and animals and also the food we eat.
Microorganisms, also called microbes, are sometimes pathogenic in nature, i.e., they can cause diseases. However, very few microorganisms are pathogens. They are crucial life forms on earth that find applications in industrial, medicinal and agricultural fields.
It would not have been possible to study the vast field of microorganisms without the discovery of microscopes. Microscope is an optical instrument that magnifies small objects which could otherwise be not seen with naked eyes. It was discovered in the 17th century and is of two types: simple microscope and compound microscope.
Most of the microorganisms are unicellular, meaning they perform all their cellular functions in a single cell while some are multicellular. They can be prokaryotic in nature, meaning they do not have a membrane-bound nucleus or they can also be eukaryotic, having a membrane-bound nucleus.
The evolution of microorganisms has been in process since 2 billion years ago. The majority of life forms on the Earth are microbial. Studying the evolution of microbiology will help in understanding the origin of other life forms. The evolution of microbiology and microorganisms is an ongoing process because microbes are one life form that have a greater possibility of genetic variation, by methods such as genome reduction and horizontal gene transfer.
In 1969, R.H Whittaker gave a classification system where he classified organisms based on mode of nutrition and cell type into five five kingdoms:
- Monera: This group includes prokaryotic and unicellular organisms such as bacteria.
- Protista: This group includes eukaryotic and unicellular organisms such as algae.
- Fungi: This group includes eukaryotic and multicellular organisms that cannot perform photosynthesis such as yeast, mould and mushroom.
- Plantae: This group includes eukaryotic and multicellular organisms that contain chlorophyll and can synthesise their own food such as ferns and mosses.
- Animalia: This group includes eukaryotic, multicellular organisms that cannot perform photosynthesis that can respond to stimuli and have a specialised nervous system. Example: insects, birds, human and fish, etc.
However, in 1978 Carl Woese divided organisms into three domains that are applicable till today. The three domains are:
- Bacteria: They have a cell wall that is made up of peptidoglycan.
- Archaea: Their cell walls, if present, lack peptidoglycan.
- Eukarya: This domain includes:
- Protists
- Fungi
- Plants
- Animals
Viruses and other acellular components are not classified in this system. They have a separate system of classification.
Refer: Difference between Archaea and Bacteria
History of Microbiology
The field of microbiology is an ancient branch that has blossomed because of the contributions of several scientists who dedicated their time in studying the diversity of microorganisms. Let us look at them briefly.
The existence of microorganisms was first suggested by Aristotle in the 4 BC. It was in the 13th century when people realised that ground pieces of glass gave a greater magnifying power and minute particles could be observed which otherwise could not be seen with naked eyes.
Later Roger Bacon suggested that invisible living creatures were the cause of diseases. Girolamo Fracastoro gave the term syphilis to an outbreak in Europe that affected the French soldiers in the 1400s. Athanasius Kircher described invisible organisms found in milk, meat and decaying bodies as worms.
Francesco Stelluti made the first microscopic observations of bees and weevils between 1625 and 1630 on a microscope probably supplied by Galileo. Robert Hooke then observed the fruiting bodies of moulds in a microscope. This made him the first scientist to describe microorganisms.
Antonie van Leeuwenhoek was the first microbiologist to describe bacteria. He is considered as the father of microbiology who was also an amateur microscopist. He dedicated his life to constructing simple microscopes made up of double convex glass lenses.
The contributions of other scientists include:
- John Needham & Francesco Redi: They gave the spontaneous theory of generation which suggested that living organisms arose from nonliving matter.
- Nicolas Appert: He is known as the father of food science because he invented methods for airtight food preservation.
- Edward Jenner: He was a British physician who pioneered in the field of vaccination.
- Louis Pasteur: He was a French scientist who gave the process of pasteurisation that eliminates pathogens and extends the shelf life of food products.
- Paul Ehrlich: He discovered antimicrobial agents.
- Alexander Fleming: He discovered the first antibiotic, penicillin.
- Dmitri Ivanovsky: He contributed to the field of virology.
- Robert Koch: He gave Koch’s postulates that described the relationship between a microbe and disease.
Challenges in the Study of Microbial Evolution
The study of evolution could be done by comparing phenotypic characteristics such as shape of beak, seed and leaf shapes and morphology of bone. With the discovery of DNA, it became evident that the characteristics of an organism were related to its genetic composition. Thus, came to light the challenge of phenotype-genotype connection. The microorganisms are minute organisms that cannot be compared on the basis of their phenotypic characteristics. They display a vast array of genomic variability that makes the study of evolution complex.
Sexual reproduction in non-microbial forms appear to give a greater genetic diversity but in fact microorganisms demonstrate greater genomic plasticity than organisms that reproduce sexually. They can undergo horizontal gene transfer, such that they can share their genome even with distantly related microbes and put it to use immediately.
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Also Read:
- Classification of Microorganisms
- Role of Microbes in Industrial Products
- Microbiology MCQ with Answers Keys
