Humans and the Microbial World

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  • Topic: Bacteria, Archaea, Microbiology
  • Pages : 25 (2155 words )
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  • Published : January 17, 2013
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Chapter 1
Humans and
the Microbial
World
A Glimpse of History
 Science of microbiology born in 1674
 Antony van Leeuwenhoek (1632–1723)
• Made simple magnifying glass
• Studied lake water
• Observed ‘animalcules’

 Robert Hooke
• Also credited with discovery
• Described ‘microscopical
mushroom’ (common bread
mold) in 1665

1

Importance of Microorganisms
 Microorganisms are
foundation for all life
on earth
 Have existed for ~3.5
billion years
 Plants, animals,
modern
microorganisms all
evolved from ancestral
bacteria
 Our life depends on
their activities

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Lens
Specimen holder

Focus screw

Handle

© Kathy Talaro/Visuals Unlimited

The Dispute Over Spontaneous Generation
 Theory of Spontaneous Generation
• “Life arises spontaneously from non-living material” • Theory had supporters and detractors
• Detractors included
– Francesco Redi
– Louis Pasteur
– John Tyndall
• Each contributed to disproving the theory

2

The Dispute Over Spontaneous Generation
 Italian biologist and physician Francesco Redi
 Demonstrated worms on rotting meat came from
eggs of flies landing on meat (1668)





Placed meat in two jars
Covered one jar with gauze
Gauze prevented flies from depositing eggs
No eggs  no worms

 Took another 200 years to convincingly disprove
spontaneous generation of microorganisms
• One reason: conflicting results between laboratories

The Dispute Over Spontaneous Generation
 Multiple contributions helped define
 Some labs demonstrated boiled broths still
produced microorganisms
 Other labs contradicted their results
• Boiled broths longer; sealed flasks by melting necks
• Broths remained sterile unless neck cracked

 Controversy still unsolved
• Some argued heating destroyed “vital force”
necessary for spontaneous generation

3

The Dispute Over Spontaneous Generation





French chemist Louis Pasteur
Considered “father of modern microbiology”
Demonstrated air is filled with microorganisms
Filtered air through cotton plug
• Observed trapped microorganisms
• Many looked identical to those found in broths

The Dispute Over Spontaneous Generation
 Developed swan-necked flask
• Boiled infusions remained sterile despite opening to air • Ended arguments that unheated air or broths
contained “vital force” necessary for spontaneous
generation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Air escapes from
open end of flask.

Microorganisms from
air settle in bend.

Years

1

Broth sterilized—
air escapes.

2

Broth allowed
to cool slowly—
air enters.

Hours/days

3

Broth stays sterile
indefinitely.

4

Flask tilted so that
the sterile broth comes
in contact with microorganisms from air.

5

Bacteria multiply
in broth.

4

The Dispute Over Spontaneous Generation
 Some scientists remained skeptical
 Pasteur’s results not fully reproducible
 English physicist John Tyndall finally explained
conflicting data
• Proved Pasteur correct
• Sterilizing broths required different times
• Some sterilized in 5 minutes
• Others not despite 5 hours!

• Realized hay infusions contained heat-resistant
microbes

The Dispute Over Spontaneous Generation
 In same year (1876), German botanist
Ferdinand Cohn discovered endospores
• Heat-resistant form of bacteria

 Following year, Robert Koch demonstrated
anthrax caused by a spore-forming bacterium
 Extreme heat resistance of endospores explains
differences between Pasteur’s results and those
of other investigators
• Pasteur used broths made with sugar or yeast extract
• Highlights importance of reproducing all conditions as
closely as possible when conducting research

5

Microbiology: A Human Perspective
 We could not survive without microorganisms
...
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