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Chapter 1. Microorganisms and Microbiology. Chapter outline. 1.1 What is a microbe? 1.2 The importance of Microbiology 1.3 Microbes in our lives 1.4 The history of microbiology 1.5 Important events in the development of microbiology. Concepts.

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Chapter 1

Microorganisms and Microbiology


Chapter outline

1.1 What is a microbe?

1.2 The importance of Microbiology

1.3 Microbes in our lives

1.4 The history of microbiology

1.5 Important events in the development

of microbiology

  • Microorganisms are responsible for many of the changes observed in organic and inorganic matter (e.g., fermentation and the carbon, nitrogen and sulfur cycles that occurred in nature.
  • The development of microbiology as a scientific discipline has depended on the availability of the microscope and the ability to isolate and grow pure cultures of microorganisms.
  • Microbiology is a large discipline, which has a great impact on other areas of biology and general human welfare

1.1 What is a microbe?

The word microbe (microorganism) is used to describe an organism that is so small that can not be seen without the use of a microscope. Viruses, bacteria, fungi, protozoa and some algae are all included in this category.


Our world is populated by invisible creatures too small to be seen with the unaided eye. These life forms, the microbes or microorganisms, may be seen only by magnifying their image with a microscope.


Microbial world


Infectious agents(non-living)

Prokaryotes (unicellular)







Algae (unicellular or multicellular)

Fungi (unicellular or multicellular)

Protozoa (unicellular)

Other (multicellular organisms)


The size and cell type of microbes

Most of the bacteria, protozoa, and fungi are single-celled microorganisms, and even the multicelled microbes do not have a great range of cell types. Viruses are not even cells, just genetic material surrounded by a protein coat and incapable of independent existence.


1.2 The importance of microbiology

Microbes impinge on all aspects of life, just a few of these are listed below:


The environment





The environment

  • Medicine
  • Food
  • Biotechnology
  • Research

Press here to continue


Microbes are responsible for the geochemical cycles. They are found in association with plants in symbiotic relationships. Some microbes are devastating plant pathogens, but others may act as biological control agents against diseases.


The disease-causing ability of some microbes is well known. However, microorganisms have also provided us with the means of their control in the form of antibiotics and other medically important drugs.


Microbes have been used to produce food, from brewing and wine making, through cheese production and bread making, to the manufacture of soy sauce. But microbes are also responsible for food spoilage.


Traditionally microbes have been used to synthesize important chemicals. The advent of genetic engineering techniques has led to the cloning of polypeptides into microbes.


Microbes have been used as model organisms for the investigation of biochemical and genetical processes. Millions of copies of the same single cell can be produced very quickly and give plenty of homogeneous experimental material. Most people have no ethical objections to experiments with these microorganisms.


1.3 Microbes in our lives

  • Microorganisms as Disease Agents
  • Microorganisms and Agriculture
  • Microorganisms and the Food Industry
  • Microorganisms, Energy, and the Environment
  • Microorganisms and the Future

Microbial physiology

Microbial genetics

Microbial Morphology



Branches of Microbiology




Microbial ecology

Molecular biology

Microbial taxonomy

Phycology or Algology


The future of microbiology is bright

Microbiology is one of the most rewarding of professions, because it gives its practitioners the opportunity to be in contact with all the other natural science and thus to contribute in many different ways to the betterment of human life.


1.4 The history of microbiology

In the field of observation, chance favors only prepared minds.

------ Louis Pasteur


The discovery of microorganisms

The spontaneous generation conflict

The recognition of microbial role in disease

The discovery of microbial effects on organic and inorganic matter

The development of microbiology in this century


The discovery of microorganisms

Antony van Leeuwenhock (1632-1723)

The first person to accurately observe and describe microorganisms


The first person to observe and describe microorganisms was the amateur microscopist Antony van leeuwenhoek of Delft, Holland.

Leeuwenhock made his simple, single-lens microscope which could amplify the object being viewed 50 – 300 times. Between 1673-1723, he wrote a series of letters to the Royal Society of London describing the microbes he observed from the samples of rainwater, and humam mouth.



Object being viewed

A drawing of one of the microscopes showing the lens a; mounting pin b; and focusing screws c and d.



Leeuwenhoek’s drawings of bacteria from the human mouth.


Louis Pasteur (1822 – 1895)

Pasteur’s contributions:

  • Pasteur (1857) demonstrated that lactic acid fermentation is due to the activity of micro-organisms
  • Pasteur (1861) conflict over spontaneous generation – birth of microbiology as a science
  • Pasteur (1881) developed anthrax vaccine
  • Pasteurization

Louis Pasteur working in his laboratory


The spontaneous generation conflict

Spontaneous generation – that living organisms could develop from nonliving or decomposing matter.


Pasteur’s swan neck flasks used in his experiments on the spontaneous generation of microorganisms



Microorganisms are not spontaneously generated from inanimate matter, but are produced by other microorganisms


Robert Koch (1843 – 1910)

The recognition of microbial role in disease

Robert Koch in his laboratory


Koch’s postulates

  • The microorganisms must be present in every case of the disease but absent from healthy organisms.
  • The suspected microorganisms must be isolated and grown in a pure culture.
  • The disease must result when the isolated microorganisms is inoculated into a healthy host.
  • The same microorganisms must be isolated again from the diseased host

The Golden age of microbiology

  • Koch and pure cultures
  • Fermentation and Pasteurization
  • Germ theory of disease
  • Vaccination

The discovery of microbial effects on organic and inorganic matter

  • The Russian microbiologist Winograsky discovered that soil bacteria could oxidize iron, sulfur and ammonia to obtain energy, and also isolated nitrogen–fixing bacteria.
  • Beijerinck made fundamental contributions to microbial ecology. He isolated Azotobacter and Rhizobium.

Alexander Fleming (1881-1955)

Sir Alexander Fleming discovered the antibiotic penicillin. He had the insight to recognize the significance of the inhibition of bacterial growth in the vicinity of a fungal contaminant.


1.5 Important events in the development of microbiology

  • Date Microbiological History
  • 1676 Leeuwenhoek discovers "animalcules"
  • Pasteur shows that lactic acid fermentation is due to a
  • microorganism
  • Pasteur shows that microorganisms do not arise by
  • spontaneous generation
  • 1867 Lister publishes his work on antiseptic surgery
  • 1869 Miescher discovers nucleic acids
  • 1876-1877 Koch demonstrates that anthrax is caused by Bacillus
  • anthracis
  • Laveran discovers Plasmodium, the cause of malaria
  • 1881 Koch cultures bacteria on gelatin
  • Pasteur develops anthrax vaccine
1884 Koch's postulates first published Metchnikoff describes

phagocytosis Gram stain developed

1887 Petri dish (plate) developed by Richard Petri

  • Beijerinck isolates root nodule bacteria
  • Beijerinck proves that a virus particle causes the tobacco

mosaic disease

1921 Fleming discovers lysozyme

1923 First edition of Bergey's Manual

1928 Griffith discovers bacterial transformation

1929 Fleming discovers penicillin

  • Ruska develops first transmission electron microscope

1935 Stanley crystallizes the tobacco mosaic virus


Avery shows that DNA carries information during

  • transformation Waksman discovers streptomycin
  • Watson and Crick propose the double helix structure
  • for DNA
  • 1961-1966 Cohen et al use plasmid vectors to clone genes in
  • bacteria
  • 1980 Development of the scanning tunneling microscope
  • 1983-1984 The polymerase chain reaction developed by Mullis
  • 1990 First human gene-therapy testing begun
  • Discovery of Thiomargarita namibiensis, the largest
  • known bacterium Escherichia coli genome sequenced
  • Discovery that Vibrio cholerae has two separate
  • chromosomes


1.How did Pasteur's famous experiment defeat the theory of spontaneous generation?

2.How can Koch's postulates prove cause and effect in a disease?

3.Who was the first person to use solid culture media in microbiology? What advantages do solid media offer for the culture of microorganisms?

4.What is the enrichment culture technique and why was it a useful new method in microbiology?

5.When and how Alexander Fleming discovered antibiotics?



1. Pasteur's experiments on spontaneous generation were of enormous importance for the advance of microbiology, having an impact on the methodology of microbiology, ideas on (he origin of life, and the preservation of food,to name just a few. Explain briefly how the impact of his experiments was felt on each of the topics listed.


2. Describe the various lines of proof Robert Koch used to definitively associate the bacterium Mycobacterium tuberculosis with the disease tuberculosis. How would his proof have been flawed if any of the tools he developed for studying bacterial diseases had not been available for his study of tuberculosis?



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