Microbiology (from Greek μῑκρος, mīkros, "small"; βίος,
bios, "life"; and -λογία, -logia) is the study of microorganisms,
those being unicellular (single cell), multicellular (cell colony), or
acellular (lacking cells).
Microbiology encompasses numerous
sub-disciplines including virology, parasitology, mycology and
Eukaryotic microorganisms possess membrane-bound cell organelles and
include fungi and protists, whereas prokaryotic organisms—all of
which are microorganisms—are conventionally classified as lacking
membrane-bound organelles and include eubacteria and archaebacteria.
Microbiologists traditionally relied on culture, staining, and
microscopy. However, less than 1% of the microorganisms present in
common environments can be cultured in isolation using current
means. Microbiologists often rely on molecular biology tools such
as DNA sequence based identification, example 16s rRNA gene sequence
used for bacteria identification.
Viruses have been variably classified as organisms, as they have
been considered either as very simple microorganisms or very complex
molecules. Prions, never considered microorganisms, have been
investigated by virologists, however, as the clinical effects traced
to them were originally presumed due to chronic viral infections, and
virologists took search—discovering "infectious proteins".
The existence of microorganisms was predicted many centuries before
they were first observed, for example by the Jains in India and by
Marcus Terentius Varro
Marcus Terentius Varro in ancient Rome. The first recorded microscope
observation was of the fruiting bodies of moulds, by
Robert Hooke in
1666, but the Jesuit priest
Athanasius Kircher was likely the first to
see microbes, which he mentioned observing in milk and putrid material
Antonie van Leeuwenhoek
Antonie van Leeuwenhoek is considered a father of
microbiology as he observed and experimented with microscopic
organisms in 1676, using simple microscopes of his own design.
Scientific microbiology developed in the 19th century through the work
Louis Pasteur and in medical microbiology Robert Koch.
2 The birth of bacteriology
5 See also
7 External links
Avicenna hypothesized the existence of microorganisms.
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 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
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."
In the golden age of Islamic civilization, some 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
Girolamo Fracastoro proposed that epidemic diseases were
caused by transferable seedlike entities that could transmit infection
by direct or indirect contact, or vehicle transmission.
Antonie van Leeuwenhoek, often cited as the first to experiment with
Van Leeuwenhoek's microscopes by Henry Baker
Martinus Beijerinck, the founding father of the
Delft School of
Microbiology, in his laboratory. Beijerinck is often considered as a
founder of virology, environmental microbiology, and industrial
In 1676, Antonie van Leeuwenhoek, who lived most of his life in Delft,
Holland, observed bacteria and other microorganisms using a
single-lens microscope of his own design. He is considered a
father of microbiology as he pioneered the use of simple single-lensed
microscopes of his own design. While Van Leeuwenhoek is often
cited as the first to observe microbes,
Robert Hooke made his first
recorded microscopic observation, of the fruiting bodies of moulds, in
1665. It has, however, been suggested that a Jesuit priest called
Athanasius Kircher was the first to observe micro-organisms.
Kircher was among the first to design magic lanterns for projection
purposes, so he must have been well acquainted with the properties of
lenses. He wrote "Concerning the wonderful structure of things in
nature, investigated by Microscope" in 1646, stating "who would
believe that vinegar and milk abound with an innumerable multitude of
worms." He also noted that putrid material is full of innumerable
creeping animalcules. He published his Scrutinium Pestis (Examination
of the Plague) in 1658, stating correctly that the disease was caused
by microbes, though what he saw was most likely red or white blood
cells rather than the plague agent itself.
The birth of bacteriology
Innovative laboratory glassware and experimental methods developed by
Louis Pasteur and other biologists contributed to the young field of
bacteriology in the late 19th century.
The field of bacteriology (later a subdiscipline of microbiology) was
founded in the 19th century by Ferdinand Cohn, a botanist whose
studies on algae and photosynthetic bacteria led him to describe
several bacteria including
Bacillus and Beggiatoa. Cohn was also the
first to formulate a scheme for the taxonomic classification of
bacteria, and to discover endospores.
Louis Pasteur and Robert
Koch were contemporaries of Cohn, and are often considered to be the
father of microbiology and medical microbiology, respectively.
Pasteur is most famous for his series of experiments designed to
disprove the then widely held theory of spontaneous generation,
thereby solidifying microbiology’s identity as a biological
science. One of his students, Adrien Certes, is considered the
founder of marine microbiology. Pasteur also designed methods for
food preservation (pasteurization) and vaccines against several
diseases such as anthrax, fowl cholera and rabies. Koch is best
known for his contributions to the germ theory of disease, proving
that specific diseases were caused by specific pathogenic
micro-organisms. He developed a series of criteria that have become
known as the Koch's postulates. Koch was one of the first scientists
to focus on the isolation of bacteria in pure culture resulting in his
description of several novel bacteria including Mycobacterium
tuberculosis, the causative agent of tuberculosis.
While Pasteur and Koch are often considered the founders of
microbiology, their work did not accurately reflect the true diversity
of the microbial world because of their exclusive focus on
micro-organisms having direct medical relevance. It was not until the
late 19th century and the work of
Martinus Beijerinck and Sergei
Winogradsky that the true breadth of microbiology was revealed.
Beijerinck made two major contributions to microbiology: the discovery
of viruses and the development of enrichment culture techniques.
While his work on the tobacco mosaic virus established the basic
principles of virology, it was his development of enrichment culturing
that had the most immediate impact on microbiology by allowing for the
cultivation of a wide range of microbes with wildly different
physiologies. Winogradsky was the first to develop the concept of
chemolithotrophy and to thereby reveal the essential role played by
micro-organisms in geochemical processes. He was responsible for
the first isolation and description of both nitrifying and
nitrogen-fixing bacteria. French-Canadian microbiologist Felix
d'Herelle co-discovered bacteriophages in 1917 and was one of the
earliest applied microbiologists.
Joseph Lister was the first to use phenol disinfectant on the open
wounds of patients.
A university food microbiology laboratory
Main article: Branches of microbiology
The branches of microbiology can be classified into pure and applied
sciences, or divided according to taxonomy, as is the case with
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
Fermenting tanks with yeast being used to brew beer
While some fear microbes due to the association of some microbes with
various human diseases, many microbes are also responsible for
numerous beneficial processes such as industrial fermentation (e.g.
the production of alcohol, vinegar and dairy products), antibiotic
production and act as molecular vehicles to transfer DNA to complex
organisms such as plants and animals.
Scientists have also exploited
their knowledge of microbes to produce biotechnologically important
enzymes such as Taq polymerase, reporter genes for use in other
genetic systems and novel molecular biology techniques such as the
yeast two-hybrid system.
Bacteria can be used for the industrial production of amino acids.
Corynebacterium glutamicum is one of the most important bacterial
species with an annual production of more than two million tons of
amino acids, mainly L-glutamate and L-lysine. Since some bacteria
have the ability to synthesize antibiotics, they are used for
medicinal purposes, such as
Streptomyces to make aminoglycoside
A variety of biopolymers, such as polysaccharides, polyesters, and
polyamides, are produced by microorganisms. Microorganisms are used
for the biotechnological production of biopolymers with tailored
properties suitable for high-value medical application such as tissue
engineering and drug delivery. Microorganisms are used for the
biosynthesis of xanthan, alginate, cellulose, cyanophycin,
poly(gamma-glutamic acid), levan, hyaluronic acid, organic acids,
oligosaccharides and polysaccharide, and polyhydroxyalkanoates.
Microorganisms are beneficial for microbial biodegradation or
bioremediation of domestic, agricultural and industrial wastes and
subsurface pollution in soils, sediments and marine environments. The
ability of each microorganism to degrade toxic waste depends on the
nature of each contaminant. Since sites typically have multiple
pollutant types, the most effective approach to microbial
biodegradation is to use a mixture of bacterial and fungal species and
strains, each specific to the biodegradation of one or more types of
Symbiotic microbial communities confer benefits to their human and
animal hosts health including aiding digestion, producing beneficial
vitamins and amino acids, and suppressing pathogenic microbes. Some
benefit may be conferred by eating fermented foods, probiotics
(bacteria potentially beneficial to the digestive system) or
prebiotics (substances consumed to promote the growth of probiotic
microorganisms). The ways the microbiome influences human and
animal health, as well as methods to influence the microbiome are
active areas of research.
Research has suggested that microorganisms could be useful in the
treatment of cancer. Various strains of non-pathogenic clostridia can
infiltrate and replicate within solid tumors. Clostridial vectors can
be safely administered and their potential to deliver therapeutic
proteins has been demonstrated in a variety of preclinical models.
Microbes and Man
American Society for Microbiology
Federation of European Microbiological Societies
Society for Applied Microbiology
Society for General Microbiology
Critical Reviews in Microbiology
International Journal of Systematic and Evolutionary Microbiology
Journal of Bacteriology
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