Lecture 2-Microbiology, A Historic Perspective(1)

8/11/2019 Lecture 2-Microbiology, A Historic Perspective(1)

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Life expectancy in the USA, 1900-98





What Is a Microbe?

Microbes are

organisms that

are too small to

be seen with the

unaided eye.



Units of measurement

! Unit is meter (m).

! 1 !m = 10 –6 m = 10 –3 mm

!

1 nm = 10 –9 m = 10 –6 mm

! 1000 nm = 1 !m

! 0.001 !m = 1 nm

!

unaided eye: resolution is0.4 mm (400 µm)



6



Type of Microbial Cells

•

Prokaryotic cells

– lack a true membrane-delimited nucleus

•

Eukaryotic cells

– have a membrane-enclosed nucleus

– are more complex morphologically

–

are usually larger than prokaryotic cells





Classification Schemes

• Three domain system, based ona comparison of ribosomal RNA

genes, divides microorganisms

into

–

Bacteria,

– Archaea

– Eukarya (eukaryotes)

9

Carl Woese



Domain Bacteria

•

Usually single-celled

•

Majority have cell wall with peptidoglycan

•

Most lack a membrane-bound nucleus

•

Ubiquitous and some live in extreme

environments

•

Cyanobacteria produce significant amounts ofoxygen

10



Domain Archaea

•

Distinguished from Bacteria by unique rRNA

(16S) gene sequences

•

Lack peptidoglycan in cell walls

•

Have unique membrane lipids

•

Some have unusual metabolic characteristics

•

Archaeal ribosomes are similar to eukaryotic

ribosomes

•

Many live in extreme environments (eg. high

temperature)



Domain Eukarya - E ukaryotic

•

Protists – generally larger than Bacteria and

Archaea

– algae – photosynthetic

–

protozoa – may be motile, “hunters, grazers”

– slime molds – two life cycle stages

– water molds – devastating disease in plants

•

Fungi

– yeast - unicellular

– mold - multicellular



Acellular Infectious Agents

•

Viruses – smallest of all microbes (?)

– requires host cell to replicate

– some cause diseases including cancers

–

1032 viruses on earth – >106 viral particles per ml in seawater

– everyone is infected by herpesviruses.

– we eat and breathe billions of viruses regularly.

•

Viroids and virusoids – infectious agents composed of RNA (eg. HDV)

• Prions – infectious proteins



Viruses

• Acellular.

• DNA or RNA genome.

• Genome is surrounded by aprotein coat called capsid.

•

Coat may be enclosed in a lipidenvelope.

• Viruses are replicated only whenthey are in a living host cell(intracellular parasites).

envelope

capsidNucleic acid



What Is a Microbe?

• Microbes are living creatures (except for viruses?).

– Have proteins, nucleic acids, lipid, sugars (same as us

chemically).

– Metabolize, grow, reproduce, response to environment (signs of

life).

•

Microbial genomes (many are sequenced) – Genome = organism’s total genetic content.

– The phage "-X174 (5368 bps) was sequenced by FredSanger in 1977.

– The complete genome sequence of a cellular microbe isHaemophilus influenza ( 2 million bps, 1,700 genes).

–

First draft of human genome was published in 2000.• Microbes have greatest diversity of genomes

– Important for understanding evolution.



Whose genome has been sequenced first?

http/www.jcvi.org/



Have you heard these?

•

Metagenomics

o Metagenomics (also Environmental Genomics, Ecogenomics or

Community Genomics) is the study of genetic material recovered

directly from environmental samples.

o

http://en.wikipedia.org/wiki/Metagenomics

• Synthetic biology

o http://en.wikipedia.org/wiki/Synthetic_biology



Reconstruction of the 1918 influenza virus

By Jeff Taubenberger and Johan Hultin

http://www.npr.org/templates/story/story.php?storyId=4946718

Gene sequencing

Gene reconstruction

Pathological specimen(circa 1918)

.. .

. .

Reverse genetics, Synthetic Biology

Experiment in Tissue culture

And Animal models

PCR

A mosquito in amber.

1918 Flu tissue specimen



Site of a mass grave, Brevig Mission, Seward Peninsula, Alaska

Reconstruction of the 1918 influenza virus

By Jeff Taubenberger and Johan Hultin





Microbes Are Living Organisms

•

Microbes arise only from other microbes

– No spontaneous generation

– 1688: Redi shows that flies do not spontaneously

generate – 1861: Louis Pasteur shows that microbes do not

grow in liquid until introduced from outside

No growth

Flask neck broken,

bacteria fall into and

grow in medium



Louis Pasteur

•

Disapproval of spontaneousgeneration.

•

Microbes cause fermentation.

•

Early vaccine development.

•

Pasteurization.

o 63ºC 30 min

o 72ºC 15 sec (HTST).

o 140ºC 1 sec (UHT).

o Kill pathogen and spoilage microbes.

o #sterilization.

Louis Pasteur



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?



Koch’s Postulates

• Provides means of testing hypothesis:

– “Does this germ cause that disease?”

• Organism must meet 4 criteria:

–

1. Microbe always present in diseased• Absent in healthy

– 2. Microbe is grown in pure culture

• No contamination of other microbes.

–

3. Introduce pure microbe into healthy individual

• Individual becomes sick (same disease)

– 4. Same microbe re-isolated from now-sick individual

Robert Koch





Limitations of Koch’s Postulates

• Some organisms cannot be grown in pure culture.

• Using humans in completing the postulates is

unethical (no animal model).

•

Cofactors are needed for disease development(ubiquitous pathogen).

• Some diseases develop extremely slow.

• Molecular and genetic evidence may replace and

overcome these limits.







" Beginning with Pasteur’s work,

discoveries included the relationship

between microbes and disease, immunity,and antimicrobial drugs

The Golden Age of Microbiology



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

Figure 1.21



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



Microbes Shape Human History

•

Microbial diseases change history

– Black plague in Europe

–

Smallpox in Americas•

Microbes affect food availability

– Destroy crops, preserve food

• bread, wine, cheese

• Chocolate!



Microbial Ecology and Evolution

•

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, plants

• Earth had no oxygen in atmosphere



Microbial Ecology

•

Microbes cycle most elements on earth – Nitrogen cycle

• Bacteria fix N2 to NH4

• Nitrify NH3 to NO

3

-

– Carbon cycle

• Photosynthetic microbes

fix most carbon

•

Many other conversions

– Sulfur cycle

– Phosphorus cycle



35

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



36

Amazing usage of microbiology:

Botox

! Botox is a neurotoxin made by

bacterium Clostridium botulinum.

!

Botulinum (Latin botulus ="sausage”) toxin is one of the

most poisonous naturally

occurring substances in the world.

!

A small dose of Botox decreases

muscle activity, so the muscle is

unable to contract for a period of

4 to 6 months.



The Importance of Microorganisms

• Most populous and diverse group oforganisms

• Found everywhere on the planet

•

Play a major role in recycling essentialelements

•

Source of nutrients and some carry outphotosynthesis

•

Benefit society by their production of food,beverages, antibiotics, and vitamins

•

Some cause disease in plants and animals



Summary

•

What are microbes? Three domains of life.

•

History of microbiology (germ theory, goldenage, important persons).

•

Medical microbiology, infectious diseases, andhuman history.

•

Applied and environmental microbiology.

•

Contribution of microbiology to modern

molecular biology.•

New developments in microbiology.





In 1918, a pandemic of ___________ killed ~40 million people all over the world.

A) Pneumonia

B) Influenza

C) AIDS

D) Tuberculosis

E) Cholera

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Lecture 2-Microbiology, A Historic Perspective(1)