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Chapter 28

BIO153H5 Chapter Notes - Chapter 28: Euryarchaeota, Gram Staining, Crenarchaeota

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Christoph Richter

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Key Points
Bacteria and archaea have a profound impact on humans and global
ecosystems. A few bacteria cause important infectious diseases; some
bacterial and archaea species are effective at cleaning up pollution;
photosynthetic bacteria were responsible for the evolution of the oxygen
atmosphere; bacteria and archaea cycle nutrients through every terrestrial
and paquatic environment
Bacteria and archaea have been evolving for billion of years and are
extremely sophisticated organisms. Although they are small and relatively
simple morphologically, they live in virtually every habitat know and use
remarkable diverse types of compounds in cellular respiration and
28.0 Introduction
Biologists study bacteria and bacteria and archaea for many reasons
The ubiquity and abundance of bacteria make them exceptionally important
in both human and natural economies
Bacteria have a unique compound called peptidoglycan in their cell walls
Archaea have unique phospholipids compounds containing hydrocarbons
called isoprenes in their tails in their plasma membranes
Microbes microscopic organism are bacteria or archaea, and virtually all
are unnamed and undescribed
Microbiology the study of organisms that can be seen only with the aid of a
28.1 Why Do Biologists Study Bacteria and Archaea?
Biologists study bacteria and archaea for many reasons
The ubiquity and abundance of bacteria make them exceptionally important
in both human and natural economies
Some Bacteria Cause Disease
No archaea are known to cause disease in humans
Bacteria that cause disease are said to be pathogenic
Pathogenic literally means “disease-producing”
o Have been responsible for some of the most devastating epidemics in
human history
An Infectious Disease is one spread by being passed from an infected
individual to an uninfected individual
Koch’s experiments became the basis for the germ theory of disease, which
holds that infectious diseases are caused by bacteria and viruses
Koch’s postulates are used to confirm a causative link between a specific
infectious disease and an infectious microbe:
o The microbe must be present in individuals suffering from the disease
and absent from healthy individuals

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o The organism must be isolated and grown in a pure culture away from
the host organism
o If organisms from the pure culture are injected into organisms a
healthy experimental animal, the disease symptoms should appear
o The organism should be isolated from the diseased experimental
animal, again grown in pure culture and demonstrated by its size,
shape and color to be the same as the original organism
Antibiotics are molecules that kill bacteria
Bacteria Can Clean Up Pollution
Some of the most serious pollutants in soils, rivers, and ponds consist of
organic compounds that were originally used as solvents or fuels but leaked
or were spilled into the environment
These pollutants do not dissolve in water and accumulate in sediments
Bioremediation is the use of bacteria and archaea to degrade pollutant
This is often based on complementary strategies:
o Fertilizing contaminated sites to encourage the growth of existing
bacteria and archaea that degrade toxic compounds
o Adding specific species of bacteria and archaea to contaminated sites
Bacteria or archaea that live in high-salt, high-temperature, low-temperature,
or high-pressure habitats are called extremophiles
Archaea are abundant forms of life in environments such as hot springs at
the bottom of the ocean, where water as hot as 300 degrees C emerges and
mixes with 4 degree C seawater
Understanding extremophiles may help explain how life on Earth began
Astrobiologists use extremophiles as model organisms in the search for
extraterrestrial life
How Do Small Cells Affect Global Change?
Bacteria and archaea can live in extreme environments and use toxic
compounds as food because they produce extremely sophisticated enzymes
The complex chemistry and abundance of bacteria and archaea make them
potent forces for global change
The Oxygen Revolution
No free molecular oxygen existed for the first 2.3 billion years of Earth’s
Cyanobacteria are a lineage of photosynthetic bacteria
o Were the first organisms to perform oxygenic (oxygen-producing)
Cyanobacteria were responsible for a fundamental change in Earth’s
atmosphere to one with a high concentration oxygen
Once oxygen was common in the oceans, aerobic respiration became
Prior to this, only anaerobic respiration was possible and cells had to use
compounds other than oxygen as the final electron acceptor
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