Unit 1: Diversity
Lesson 6: The Prokaryotes: Eubacteria & Archaea
How important are microorganisms? We are surrounded by billions of microscopic organisms!
Our bodies are inhabited by countless organisms that go unnoticed. Microorganisms are the cause of
most infectious diseases; yet, they also can produce the substances necessary to fight off diseases.
Microorganisms also play key roles in entire ecosystems. They recycle nutrients and are important
producers. Our own bodies contain microorganisms that aid in digestion.
Activity:
Some microorganisms can reproduce very quickly. In this activity, you will model the growth
rate of a population of bacteria under ideal conditions. In this model, each bacterial cell grows and
divides once each hour, so the population doubles in size each hour.
Equipment and Materials:
 Large bucket
 Eyedropper
 Small and large graduated cylinders
 Water
Procedure:
1. Place 1 drop of water in a large bucket. This drop represents the size of the starting
population. Predict how full the bucket will be after the population has doubled 10 times.
2. Create a table to record the size of the population.
3. Add 1 more drop of water to the bucket. This drop represents the doubling of the population
during the first hour.
4. Add 2 more drops of water to the bucket to represent the doubling of the population during
the second hour.
5. Keep doubling the population by adding drops of water to the bucket. When you reach the
fourth hour, substitute 1mL of water for 16 drops. Begin recording the population size in
millilitres instead of drops. Stop when the population has doubled 10 times. Compare your
prediction in step 1 with the data from your model. Now predict how full the bucket will be
after the population has doubled another 10 times. Continue doubling the population to test
your prediction.
Analysis:
A) Did the growth rate of the model bacteria population surprise you? Explain.
B) How might the ability to reproduce quickly benefit microscopic organisms?
C) How might understanding how quickly a microscopic organism can reproduce help a physician
treat a patient with an infection?
D) Brainstorm examples in everyday life where microscopic organisms grow quickly.
Unit 1: Diversity
Lesson 6: Prokaryotes: Eubacteria and Archaea
The Eubacteria domain and Archaea domain are both prokaryotic. This means that they are singlecelled organisms and they lack membrane-bound organelles. Prokaryotes are the smallest organism on
the earth. They can be between 1µm to 2µm. [µm (micrometre) or a micron is a unit of length equal to
one millionth of a metre.
Prokaryotes are so small that if you were to line them up on the dot on top of this “i”, you could
expect to see 500 to 1000 of them in a row! Despite their small size, they are a dominate form of life
that exist in vast amounts and live in every imaginable habitat. There are more than 100 trillion
bacteria living on and within your body. This is more than the total of all the other cells in your body.
Even though they are so prevalent, scientists have only isolated and identified approximately 1% of
the total number of species.
Importance of Prokaryotes:
“Negative” Effects
Positive Effects
NB: It might be considered negative for the
infected species, but not so for the bacteria or
for predators of the infected species.
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Responsible for many
diseases.
- Infectious bacteria and
other disease-causing
agents (virus,
microorganism) are known
as pathogens.
Bacteria can also infect
livestock and crops and
therefore threaten our
primary food source
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Important effect on ecosystems
- Act as decomposers
- Help cycle nutrients
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Bacteria reside in the intestines of animals and aids in
digestion in a mutualistic relationship. [mutualism: a
relationship between two species that live in very close
association with each other, whereby each benefits from
the association.]

Bacteria used for commercial use
- Making yogurt, cheese, chocolate
- Chocolate is made using yeast and bacteria to ferment cacao
beans
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The Domain Eubacteria:
Bacteria can produce antibiotics [a substance that can
kill or weaken microorganisms, natural antibiotics are
produced by bacteria or fungi, whereas synthetic
antibiotics are manufactured.
Characteristics of Bacteria:
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A bacterium’s chromosome is a single loop of DNA that is found in a region called the nucleoid
Ribosomes (site of protein synthesis), are scattered throughout the cytoplasm
Often have one ore more flagella for movement and small hair-like structures called pili
In addition to a single chromosome, many bacteria have one or more plasmids in their
cytoplasm.
o A plasmid: is a small loop of DNA often found in prokaryotic cells; usually contains a
small number of genes. These genes are not essential for cellular functions but often
provide some advantage to the cell such as giving the bacteria resistance to antibiotics
Cell wall composed primarily of peptidoglycan. Peptidoglycan makes the cell wall strong and
rigid.
Some bacteria is surrounded by a sticky capsule, which is an outer layer on some bacteria;
provides some protection for the cell.
Bacteria Shapes & Arrangements:
Bacterial
Shape:
Coccus (plural: cocci):
round bacterial cell
Bacillus (plural: bacilli):
rod shaped
Spirillum (plural: spirilli):
spiral shaped
Bacterial
Arrangements:
Diplo: (occur in pairs)
Staphylo: (occurs in
clumps)
Strepto: (occurs in
strings)
Key Features of the Six Major Groups of Bacteria:
Group:
Key Feature:
proteobacteria
 Some are photosynthetic but use a form of photosynthesis that differs from
(purple
that of plants
bacteria)
 Ancient forms of these bacteria were the likely ancestors of eukaryotic
mitochondria
 Some are nitrogen fixing
 They are responsible for many diseases, including bubonic plague, gonorrhoea,
dysentery, and some ulcers
green bacteria
 They use a form of photosynthesis that differs from that of plants
 They are usually found in salt-water environments or hot springs
cyanobacteria
(blue-green
algae)
gram-positive
bacteria
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They use a form of photosynthesis similar to plants and other eukaryotes
Ancient forms of these bacteria were the likely ancestors of eukaryotic
chloroplasts
They play major roles as producers and nitrogen fixers in aquatic ecosystems
They form symbiotic relationships with fungi
They cause many diseases, including anthrax, strep throat, bacterial
pneumonia and meningitis
They are used in food production (for example, lactobacillus is used in yogurt
and probiotic products)
Some have lost their cell wall
One type – mycoplasmas – are the smallest known cells (0.1µm to 0.2µm)
[Gram positive versus Gram negative refers to how bacteria react to a stain invented by
Danish bacteriologist Hans Christian Joachim Gram)
spirochetes
Chlamydias
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Their spiral-shaped flagellum is embedded in their cytoplasm
They move with a corkscrew motion
They cause syphilis
Symbiotic spirochetes in termite intestines digest wood fibre
All are parasites that live within other cells
They cause Chlamydia, one of the most common sexually transmitted
infections
They cause trachoma, the leading cause of blindness in humans
Disease
Bubonic plague
Gonorrhoea
Dysentery
Ulcers
Anthrax
Strep throat
Bacteria pneumonia
Meningitis
Syphilis
Chlamydia
Trachoma
Chloera
Diphtheria
Lyme disease
Pertussis
Rocky Mountain
spotted fever
Scarlet Fever
Tetanus
Useful websites:
Characteristics of the Disease
Acute, diarrheal infection
Bacteria responsible
Vibrio cholera
Corynebacterium
diphtheria
Borrelia burgdorferi
Bordetella pertussis
Rickettsia rickettsil
Streptococcus pyogenes
Clostridium tetani
http://www.phac-aspc.gc.ca/id-mi/index-eng.php (public health agency of Canada)
http://www.cdc.gov/ (centre for disease control – USA)
Unit 1: Diversity
Lesson 6.1: More About Eubacteria & Archea
Metabolism of Bacteria: - How Bacteria Obtains Nutrients and Energy
Metabolism: The process involving a set of chemical reactions that modifies a molecule
into another for storage or for immediate use in another reaction or as a by-product.
Nutrients:
Autotrophic Bacteria: They assemble complex
carbon molecules from simple inorganic
chemicals such as carbon dioxide, water and
minerals that are part of the abiotic
environment.
Inorganic Chemical: a chemical that has an
abiotic origin; some simple substances that are
produced by organisms are also classified as
inorganic.
Hetertrophic Bacteria: They get their
nutrients from carbon containing organic
chemicals found in other living organisms or
their remains.
Organic Chemical: in biology, any chemical that
contains carbon and is produced by living things;
carbon dioxide is an exception – it is produced
during respiration but is classified as inorganic.
Energy:
The two primary sources of energy for living things are sunlight and chemical energy. We are most
familiar with the chemical energy contained in organic chemicals such as sugars, fats, and proteins.
Many bacteria can also get energy from inorganic chemicals such as hydrogen, sulphur and iron
compounds.
Plants and animals cannot survive without oxygen. Organisms that cannot survive without oxygen are
called obligate aerobes. Obligate aerobes use the oxygen to get energy from food. Some bacteria are
obligate aerobes.
Some bacteria are facultative aerobes. Facultative aerobes can live with or without oxygen. These
bacteria perform aerobic respiration in the presence of oxygen and, if oxygen is not present, they
perform anaerobic respiration or anaerobic fermentation. Fermentation is an anaerobic process that
releases chemical energy from food.
Some bacteria are obligate anaerobes. They cannot live in environments where oxygen is present.
Organism:
Effect of
Oxygen
on
growth:
Obligate Aerobes
- oxygen is required
- can only survive if aerobic
conditions
- dies if oxygen is absent
Example:
Mycobacterium
Facultative Aerobes
- increased growth in the
presence of oxygen
- can survive in both aerobic
and anaerobic conditions
- aerobic : respiration
- anaerobic: fermentation
Streptococcus
Obligate Anaerobes
- oxygen not required
- can only survive in
anaerobic conditions
- dies if oxygen is present
Clostridium
Reproduction of Bacteria:
Prokaryotes, such as bacteria, normally reproduce asexually.
Asexual Reproduction
Sexual Reproduction
 Single individual is the sole parent
 Two parents give rise to an offspring
 Single parent passes on all its genes to its
 Each parent passes on half of its genes to
offspring
the offspring
 Offspring are genetically identical to its
 Offspring has a unique combination of
parents
genes inherited from both parents
 Results in clones (genetically identical
 Results in greater genetic variation;
individuals); any deviations are the result
offspring vary genetically from siblings
of genetic mutations
and parents
Reproductive Strategies of Bacteria:
1. Binary Fission: the division of one parent cell into two genetically identical daughter cells.
This type of reproduction is asexual. Each daughter cell receives an exact copy of the genetic
material from the parent cell – its chromosome and plasmids. When genetic material is copied,
it is possible to make mistakes. These lead to mutations. As bacteria reproduce very quickly,
they mutate more often than organisms that reproduce more slowly. A bacterial gene mutates
roughly 1000 times as often as eukaryotic gene. These mutations increase the genetic diversity
in populations of bacteria.
2. Conjugation: a form of sexual reproduction in which two cells join to exchange genetic
information. Conjugation allows bacteria to increase their genetic diversity by gaining new
DNA. In conjugation, on e bacterial cell passes a copy of a plasmid to a nearby cell through a
hollow pilus.
3. Transformation: Occurs when a cell picks up a loose fragment of DNA from its surroundings
and uses it. These DNA fragments may have been released into the environment when other
cells died. If the new DNA came from a different species, the process is called horizontal
gene transfer (aka: lateral gene transfer).
4. Endospores: In unfavourable conditions, bacteria can create endospores to ensure their
survival. Endospores are a dormant structure that forms inside of certain bacteria, around its
chromosome, in response to stress. It is a highly resistant structure that protects the cell’s
chromosomes from damage. Endospores can withstand extreme conditions and remain dormant
until conditions improve, often for many years. (ex: living bacterial endospores in Egyptian
mummies)
Disease and Antibiotics:
Bacteria are responsible for many diseases by producing and releasing toxins. Some bacteria
contain toxic compounds that are released once the cell dies. Antibiotics can be used to kill
bacteria that cause disease. Penicillin, for example, is a type of antibiotic that is derived from
bread mould as discovered by Alexander Flemming in 1928. Most antibiotics are derived from
bacteria or fungi. Prokaryotes and fungi are often in direct competition with each other for food
and resources and produce antibiotic substances as a form of chemical warfare. Antibiotics are
immensely valuable to humans to fight off diseases caused by bacteria. Unfortunately, the overuse
of antibiotics has lead to the rise of antibiotic-resistant strains of bacteria, rendering the
antibiotics useless.
The Domain Archaea:
There are three branches of Archaea namely: euryarchaeota, crenarchaeota, korarchaeota. The
following table highlights some characteristics of Archaea from the euryarchaeota.
Euryarchaeota
Key Features
Subgroup
Methangoens
 Live in low-oxygen environments (ex: sediments of swamps, lakes,
marches, sewage lagoons; digestive tracts of mammals and insects)
 Generate energy by converting chemical compounds into methane
gas which is released into the atmosphere
Halophiles
 Salt-loving organisms that live in high saline environments (ex:
Dead Sea; food preserved by salting)
 Most are aerobic and get energy from organic food molecules
 Some use light as a secondary energy source
Extreme thermophiles
 They live in extremely hot environments (ex: hot springs and
hydrothermal vents on the ocean floor)
 Optimal temperature for growth is 70oC to 95oC
Psychrophiles
 They are cold-loving organisms found mostly in the Antartic and
Arctic oceans, and cold ocean depths
 Optimal temperature for growth is -10oC to -20oC.
Homework:
Question # 1, 4, 5, 9, 12, 14
Solutions: