Transcript Spontaneous Generation

Microbiology
• Brief Review
• Spontaneous
Generation and
Biogenesis
What is Microbiology?
Microbes, or microorganisms are minute
living things that are usually unable to be
viewed with the naked eye.
What are some examples of microbes?
Bacteria, fungi, protozoa, algae, viruses
are examples!
Some are pathogenic
“Germ” refers to a rapidly growing cell.
Review
What is Microbiology?
Microbes:
•Decompose organic waste
•Are producers in the ecosystem by
photosynthesis
•Produce industrial chemicals such as
ethyl alcohol and acetone
•Produce fermented foods such as
vinegar, cheese, and bread
What is Microbiology?
Knowledge of Microbes allows humans to
Prevent food spoilage
Prevent disease occurrence
Led to aseptic techniques to prevent
contamination in medicine and in
microbiology laboratories.
History of Microbiology
Ancestors of bacteria were the first life on Earth.
Discovery of Microorganisms
• Antony van
Leeuwenhoek
(1632-1723)
– First person to
observe and
describe microorganisms
accurately
– Teeth scrapings,
pond water
Figure 1.1b
Van Leeuwenhoek 1684
Biogenesis vs. Spontaneous Generation
Two hypotheses:
The hypothesis that living organisms arise
from nonliving matter is called spontaneous
generation. According to spontaneous
generation, a “vital force’ forms life.
The Alternative hypothesis, that the living
organisms arise from preexisting life, is
called biogenesis. (Rudolf Virchow)
The Conflict over Spontaneous
Generation
• Spontaneous Generation
– living organisms can develop from nonliving
or decomposing matter
• Francesco Redi (1626-1697)
– disproved spontaneous generation for large
animals
– showed that maggots on decaying meat came
from fly eggs
History of Microbiology
Redi filled six jars with decaying meat.
Conditions
Results
3 jars covered with
fine net
3 open jars
No maggots
Maggots appeared
From where did the maggots come?
What was the purpose of the sealed jars?
Spontaneous generation or biogenesis?
But could spontaneous generation be
true for microorganisms?
• John Needham (1713-1781)
– his experiment:
mutton broth in flasks  boiled, allowed to cool sealed
– results: broth became cloudy and contained
microorganisms
• Lazzaro Spallanzani (1729-1799)
– his experiment:
broth in flasks sealed  boiled
– results: no growth of microorganisms
• What about ability of air to generate life? It was not allowed to
enter
• Critics claimed he “killed the vital force”
Louis Pasteur (1822-1895)
• His experiments
– placed nutrient solution in
flasks
– created flasks with long,
curved necks
– boiled the solutions
– left flasks exposed to air
• results: no growth of
microorganisms
Figure 1.3
History of Microbiology
1861: Louis Pasteur demonstrated that
microorganisms are present in the air.
Conditions
Results
Nutrient broth placed Microbial growth
in flask, heated, not
sealed
Nutrient broth placed No microbial growth
in flask, heated, then
sealed
Spontaneous generation or biogenesis?
Final blow to theory of
spontaneous generation
• John Tyndall (1820-1893)
– demonstrated that dust carries microorganisms
– showed that if dust was absent, nutrient broths
remained sterile, even if directly exposed to air
– also provided evidence for the existence of
exceptionally heat-resistant forms of bacteria