What is Microbiology?
Microbiology is a branch of biological science that studies all living organisms that are too small to be visible to the naked eye. This diverse group of generally minute simple life-forms includes bacteria, archaea, algae, fungi, protozoa, and viruses. The field is concerned with the structure, function, and classification of such organisms and with ways of both exploiting and controlling their activities.
In microbiology we can study organisms in great detail and observe their life processes while they are actively metabolizing, growing, reproducing, aging, and dying.
By modifying their environment we can alter metabolic activities, regulate growth, and even change some details of their genetic pattern-all without destroying the organisms.
However, microbiology also is an applied science, helping agriculture, health and medicine and maintenance of the environment, as well as the biotechnology industry. Microbiologists study microbes at the level of the community (ecology and epidemiology), at the level of the cell (cell biology and physiology) and at the level of proteins and genes (molecular biology).
History Of Microbiology
Early History Of Microbiology
The existence of microorganisms was hypothesized for many centuries before their actual discovery.
The existence of unseen microbiological life was postulated by Jainism which is based on Mahavira’s teachings as early as the 6th century BCE. Paul Dundas notes that Mahavira asserted the existence of unseen microbiological creatures living in earth, water, air, and fire.
Jain scriptures describe nigodas which are sub-microscopic creatures living in large clusters and having a very short life, said to pervade every part of the universe, even in tissues of plants and flesh of animals.
The Roman Marcus Terentius Varro made references to microbes when he warned against locating a homestead in the vicinity of swamps “because there are bred certain minute creatures which cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and thereby cause serious diseases.”
Persian scientists hypothesized the existence of microorganisms, such as Avicenna in his book The Canon of Medicine, Ibn Zuhr (also known as Avenzoar) who discovered scabies mites, and Al-Razi who gave the earliest known description of smallpox in his book The Virtuous Life (al-Hawi).
In 1546, Girolamo Fracastoro proposed that epidemic diseases were caused by transferable seedlike entities that could transmit infection by direct or indirect contact, or vehicle transmission.
First microscope/first microorganisms visualized
Microbiology essentially began with the development of the microscope. Through a lens that had a magnification of roughly 300X, he was able to visualize bacteria for the first time (from scrapings off his teeth.)
Although others may have seen microbes before him, it was Antonie van Leeuwenhoek, a Dutch draper whose hobby was lens grinding and making microscopes, who was the first to provide proper documentation of his observations.
However, Robert Hooke is credited with publishing the first drawings of microorganisms in the scientific literature. In 1665 he published a highly detailed drawing of the fungus Mucor in his book Micrographia.
Development of germ theory
The human body was recognized as a source of infection by three scientists
- Dr. Oliver Wendall Holmes found that women who gave birth at home were less likely to develop infections than those who delivered in a hospital.
- Dr. Ignaz Semmelweis linked infections with physicians who went directly from the autopsy room to the maternity ward without washing their hands.
- Joseph Lister introduced aseptic techniques, including both hand-washing and using heat for sterilization.
The two people most credited with the acceptance of the germ theory were Louis Pasteur and Robert Koch
Pasteur is credited with the theory of biogenesis, noting that all living things come from something rather than the prevailing view at the time of spontaneous generation. He claimed that many diseases were caused by microbes (rather than by sin, God’s anger, and other potential causes.) He showed that microorganisms are responsible for fermentation and spoilage and developed the method called pasteurization still used today. He also developed rabies and anthrax vaccines.
Koch is the author of “Koch’s postulates” the scientific series of steps that proved the germ theory and which has been used in scientific studies since (with some revisions.) He identified the cause of tuberculosis, anthrax, and cholera.
Since that time, a few landmarks include:
1892 – Dmitri Iosifovich Ivanoski discovered the first virus.
1928 – Alexander Fleming discovered penicillin.
1995 – The first microbial genomic sequence was published.
Development of Microbiology.
In the late 1800s and for the first decade of the 1900s, scientists seized the opportunity to further develop the germ theory of disease as enunciated by Pasteur and proved by Koch. There emerged a Golden Age of Microbiology during which many agents of different infectious diseases were identified.
Many of the etiologic agents of microbial disease were discovered during that period, leading to the ability to halt epidemics by interrupting the spread of microorganisms.
Despite the advances in microbiology, it was rarely possible to render life‐saving therapy to an infected patient. Then, after World War II, antibiotics were introduced to medicine. The incidence of pneumonia, tuberculosis, meningitis, syphilis and many other diseases declined with the use of antibiotics.
Work with viruses could not be effectively performed until instruments were developed to help scientists see these disease agents. In the 1940s, the electron microscope was developed and perfected.
In that decade, cultivation methods for viruses were also introduced, and the knowledge of viruses developed rapidly. With the development of vaccines in the 1950s and 1960s, such viral diseases as polio, measles, mumps, and rubella came under control.
Modern microbiology reaches into many fields of human endeavor, including the development of pharmaceutical products, the use of quality‐control methods in food and dairy product production, the control of disease‐causing microorganisms in consumable waters, and the industrial applications of microorganisms.
Microorganisms are used to produce vitamins, amino acids, enzymes, and growth supplements. They manufacture many foods, including fermented dairy products (sour cream, yogurt, and buttermilk), as well as other fermented foods such as pickles, sauerkraut, bread, and alcoholic beverages.
One of the major areas of applied microbiology is biotechnology. In this discipline, microorganisms are used as living factories to produce pharmaceuticals that otherwise could not be manufactured.
These substances include the human hormone insulin, the antiviral substance interferon, numerous blood‐clotting factors, and clot-dissolving enzymes, and a number of vaccines.
Bacteria can be re-engineered to increase plant resistance to insects and frost, and biotechnology will represent a major application of microorganisms in the next century.
Branches of microbiology
The branches of microbiology can be classified into pure and applied sciences. Microbiology can be also classified based on taxonomy, in the cases of bacteriology, mycology, protozoology, and phycology.
There is considerable overlap between the specific branches of microbiology with each other and with other disciplines, and certain aspects of these branches can extend beyond the traditional scope of microbiology In general the field of microbiology can be divided into the more fundamental branch (pure microbiology) and the applied microbiology (biotechnology).
- Bacteriology: the study of bacteria
- Mycology: the study of fungi
- Protozoology: the study of protozoa
- Phycology/algology: the study of algae
- Parasitology: the study of parasites
- Immunology: the study of the immune system
- Virology: the study of viruses
- Nematology: the study of nematodes
- Microbial cytology: the study of microscopic and submicroscopic details of microorganisms
- Microbial physiology: the study of how the microbial cell functions biochemically. Includes the study of microbial growth, microbial metabolism and microbial cell structure
- Microbial pathogenesis: the study of pathogens which happen to be microbes
- Microbial ecology: the relationship between microorganisms and their environment
- Microbial genetics: the study of how genes are organized and regulated in microbes in relation to their cellular functions Closely related to the field of molecular biology
- Cellular microbiology: a discipline bridging microbiology and cell biology
- Evolutionary microbiology: the study of the evolution of microbes. This field can be subdivided into:
- Microbial taxonomy: the naming and classification of microorganisms
- Microbial systematics: the study of the diversity and genetic relationship of microorganisms
- Generation microbiology: the study of those microorganisms that have the same characters as their parents
- Systems microbiology: a discipline bridging systems biology and microbiology.
- Molecular microbiology: the study of the molecular principles of the physiological processes in microorganisms
- Phylogeny: the study of the genetic relationships between different organisms
- Medical microbiology: the study of the pathogenic microbes and the role of microbes in human illness. Includes the study of microbial pathogenesis and epidemiology and is related to the study of disease pathology and immunology. This area of microbiology also covers the study of human microbiota, cancer, and the tumor microenvironment.
- Pharmaceutical microbiology: 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: the exploitation of microbes for use in industrial processes. Examples include industrial fermentation and wastewater treatment. Closely linked to the biotechnology industry. This field also includes brewing, an important application of microbiology.
- Microbial biotechnology: the manipulation of microorganisms at the genetic and molecular level to generate useful products.
- Food microbiology: the study of microorganisms causing food spoilage and foodborne illness. Using microorganisms to produce foods, for example by fermentation.
- Agricultural microbiology: the study of agriculturally relevant microorganisms. This field can be further classified into the following:
- Plant microbiology and Plant pathology: The study of the interactions between microorganisms and plants and plant pathogens.
- Soil microbiology: the study of those microorganisms that are found in soil.
- Veterinary microbiology: the study of the role of microbes in veterinary medicine or animal taxonomy.
- Environmental microbiology: 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
- Microbially mediated nutrient cycling
- Microbial diversity
- Bioremediation: use of micro-organisms to clean air, water and soils.
- Water microbiology (or aquatic microbiology): The study of those microorganisms that are found in water.
- Aeromicrobiology (or air microbiology): The study of airborne microorganisms.
- Biotechnology: related to recombinant DNA technology or genetic engineering.