1. Chapter 1 Lecture Outline
Microbial Life: Origin and Discovery

2. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
What Is a Microbe?
Microbes are microscopic
Through most of their lifespan
Can only be seen through a microscope
Less than about 1 mm across
10-7 m to 10-3 m
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

3. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
What Is a Microbe?
6 major groups studied by microbiologists
Prokaryotes
Bacteria
Eukaryotes
Algae
Viruses
Archaea
Protists
Fungi
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

4. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
What Is a Microbe?
Microbes are living creatures
Except for viruses, which are noncellular
Metabolize food, grow, reproduce
Have proteins, sugars, nucleic acids
Microbial genomes are sequenced
Genome = organism’s total genetic content
Complete gene sequence known for many species
Over 1000 bacteria, over 1000 archaea
Tens of thousands of viruses
Microbes have greatest diversity of genomes
Important for understanding evolution
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

5. Microbes Shape Human History
Microbes affect food availability
Destroy crops, but preserve food
Bread, wine, cheese
Chocolate!
Microbial diseases change history
Black plague in Europe
Smallpox in Americas
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

6. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Discovery of Microbes
Light microscope invented in 1600s
Quality improved continuously
Mid-1600s: Robert Hooke observes small eukaryotes
1676: van Leeuwenhoek discovers bacteria
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

7. Microbes Are Living Organisms
Microbes arise only from other microbes
No spontaneous generation
1688: Redi shows that flies do not spontaneously generate
1861: Pasteur shows that microbes do not grow in liquid until introduced from outside
Flask neck broken, bacteria fall into and grow in medium
No growth
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

8. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Germ Theory of Disease
Observations:
Germs can infect and grow on food.
Hypothesis:
Can germs infect and grow on people?
That is, do germs cause disease?
Hypothesis is testable:
Are germs found in infected tissue?
Can transmission of germs cause disease?
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

9. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Germ Theory of Disease
Pasteur’s Theory:
Transmission of germs causes disease
All Scientific Theories:
Explain many known observations
For example, transmission of rabies
Provide framework for understanding
Where do diseases come from?
Can be tested further
Do germs cause anthrax?
A scientific theory is NOT a “guess”
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

10. Koch’s Postulates Provides means of testing hypothesis:
“Does this germ cause that disease?”

11. Corollary to Germ Theory
Stop germ transmission, stop disease spread
Stop spread of germs
Epidemiology, public health measures
Resistant individuals prevent spread of germs
1798: Vaccination with cowpox prevents smallpox
Turkish physicians, Lady Montagu, Edward Jenner
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

12. Corollary to Germ Theory
Stop germ transmission, stop disease spread
Kill germ, prevent disease
Antiseptics
1865: Antiseptic surgery
Joseph Lister
Antibiotics
1929–1941: Penicillin
Alexander Fleming
Many newer antibiotics
Bacteria become resistant
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

13. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Microbial Ecology
Most microbes don’t grow on typical medium
Many live in varied conditions
Anaerobic
Bottom of swamp, in our gut
High pressure
Bottom of ocean
Hot or cold temperatures
Below 0°C to 113°C
No organic carbon
Use light for energy, CO2 for carbon
Microbes existed before animals or plants
There was no oxygen in Earth atmosphere
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

14. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Microbial Ecology
Culture some microbes in natural mud environment
Winogradsky column
Layers grow different species
Reflecting different conditions
Can see variations in nature
Yellowstone geyser runoff
Colors reflect different species
Different growth temperatures
>56°C
<50°C
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

15. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Microbial Ecology
Microbes cycle most elements on earth
Nitrogen cycle
Bacteria fix N2 to NH4
Nitrify NH3 to NO3-
Carbon cycle
Photosynthetic microbes fix most carbon
Many other conversions
Sulfur cycle
Phosphorus cycle
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

16. The Microbial Family Tree
Microbial species are difficult to classify
Difficult to distinguish by shape
Often reproduce asexually
Pass DNA to each other without reproduction
Use biochemical properties to classify
Gram stain
Ability to metabolize different substrates
Use DNA sequence to classify
Bacterial genomes are relatively small
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

18. The Microbial Family Tree
Archaea are not bacteria
Similar size, shape
Very different biochemistry
Different membranes
Archaeal ribosomes similar to eukaryotic ribosomes
Many archaea live in harsh environments
16s rRNA gene sequence
Found in all creatures
Archaea are a separate domain
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

19. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Endosymbiont Theory
How did eukaryotes arise?
DNA similar to archaea’s
Mitochondrial, chloroplast DNA
Similar to bacterial DNA
Endosymbiont theory:
Mitochondria WERE bacteria
Chloroplasts WERE cyanobacteria
Infected or eaten by other species
Ended up living together inside
Endo-sym-biosis
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

20. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Concept Quiz
Microbes include members of the following groups:
bacteria, animals, protozoa, fungi
bacteria, archaea, fungi, viruses
archaea, viruses, plants, fungi
Answer: B
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

21. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Concept Quiz
The Germ Theory of Disease provided a framework for understanding
how disease could be passed from one individual to another.
how mitochondria are descended from bacteria.
how microbes regulate global geochemical cycles.
Answer: A
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

22. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Concept Quiz
Analysis of 16s rRNA sequences showed that
plants and animals are as distant from bacteria as they are from each other.
all microbes are only distantly related to the eukaryotes.
archaea are as distant from bacteria as from eukaryotes.
Answer: C
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.