Transcript Chapter 1 Art Slides

Chapter 1
Microbial Life: Origin and
Discovery
What Is a Microbe?

Microbes are microscopic organisms
 Through
most of its lifespan
 Can only be seen through a microscope

mm (10-3 m) to 0.2 μm (2x10-7 m)
 Usually
single-celled
 Self-contained genome

Capacity to reproduce
What Is a Microbe?

Exceptions exist
1. Super-sized microbial cells
 Thiomargarita
namibiensis
“sulfur pearl of Namibia”
 Caulerpa taxifolia
“killer algae” with acres of single cell
2. Microbial communities
multicellular assemblages: biofilm, mushrooms
microscopic worms and arthropods NOT microbes
3. Living?
 viruses
 viroids
 prions
What Is a Microbe?

6 major groups studied by microbiologists
 Prokaryotes

Bacteria

Archaea
 Eukaryotes

Algae
 Viruses

Protists

Fungi
What Is a Microbe?

Microbial genomes are easily sequenced
 Genome

= organism’s total genetic content
Complete gene sequence known for many species
Over 1000 bacteria, archaea
 Tens of thousands of viruses
 First sequenced genomes
 Bacteriophage ΦX174 (1977)
 Haemophilus influenzae (1995)
 Saccharomyces cerevisiae (1996)


Microbes have greatest diversity of genomes
Important for understanding evolution
 Comparative genomics shows core genes

Why study microorganisms?
Microbes Shape Human History

Microbes affect food availability
 Destroy
crops, preserve food
bread, wine, cheese
 Chocolate!


Microbial diseases change history
 Black
plague in Europe
 Smallpox in Americas
 HIV/AIDS worldwide
Discovery of Microbes

Light microscope invented in 1600s
 Quality

mid-1600s: Robert Hooke observes small
eukaryotes (mold)
 Saw

improved continuously
“cells” in cork
1676: Antoni van Leeuwenhoek discovers bacteria
 First
to see single-celled microbes
Microbes Are Living Organisms

Microbes arise only from other microbes
 No
spontaneous generation
 1688: Francesco Redi shows that maggots do
not spontaneously generate
 1861: Louis Pasteur shows that microbes do
not grow in liquid until introduced from outside
 Contradiction
by John Tyndall:
Boiled broth still spoil
 Contaminated with endospores

Germ Theory of Disease

Observations:
 Germs

can infect and grow on food.
Hypothesis:
 Can
germs infect and grow on people?
 i.e. Do germs cause disease?

Hypothesis is testable:
 Are
germs can be found in infected tissue?
 Can transmission of germs cause disease?
Germ Theory of Disease

Pasteur’s Theory:
 Transmission

of germs causes disease
All Scientific Theories:
 Explain

e.g. Transmission of rabies
 Provide

framework for understanding
Where do diseases come from?
 Can

many known observations
be tested further
Do germs cause anthrax?
 A scientific
theory is NOT a “guess”
Koch’s Postulates

Provides means of testing hypothesis:
 “Does

this germ cause that disease?”
Organism must meet 4 criteria:
 1.

 2.

 3.

 4.
Microbe always present in diseased
Absent in healthy
Microbe is grown in pure culture
No other microbes present.
Introduce pure microbe into healthy individual
Individual becomes sick
Same microbe re-isolated from now-sick
individual
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

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
Microbial Ecology

Most microbes don’t grow on typical medium
 Many

Anaerobic


Bottom of ocean
Hot or cold temperatures


bottom of swamp, in our gut
High pressure


live in varied conditions
Below 0°C to 113°C
No organic carbon

Use light for energy, CO2 for carbon
 Microbes

existed before animals, plants
Early earth contained mainly reduced compounds,
such as ferrous iron, methane, ammonia
Microbial Ecology

Culture some microbes in
natural mud environment
 Winogradsky

column
Layers grow different species

Reflects different conditions
 Can

see variations in nature
Yellowstone geyser runoff
Colors reflect different species
 Different growth temperatures

>56°C
<50°C
Microbial Ecology

Microbes cycle most elements on earth
 Nitrogen
cycle
Bacteria fix N2 to NH4+
 Nitrify NH4+ to NO3
 Carbon
cycle
Photosynthetic microbes
fix most carbon
 Many other conversions

 Sulfur
cycle
 Phosphorus cycle
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 relatively small
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 is a separate domain

Endosymbiont Theory

How did eukaryotes arise?
 DNA similar

Mitochondrial, chloroplast DNA
 Similar

to archaea’s
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
Cell Biology Techniques

Electron microscopy
 Observation
of cell components
Eukaryotic organelles
 Membranes


Ultracentrifuge
 Separation


of cell components
Study of biochemistry of organelles
Fluorescence microscopy
 Identification

of cell components
Subcellular location of individual proteins
Genetics and DNA Revolution

Molecular genetics depends on bacteria
 Concept
of “gene” proposed for bacteria
 DNA structure
 Genetic code
 Transcription, translation
 Restriction enzymes
 Recombinant DNA
 Cloning
 PCR reaction
 E. coli has best understood genome