Biodiversity
Prokaryotes
Prokaryotes are the most numerous living
organisms (the number of cells in a
handful of fertile soil is greater than the
number of humans who have ever existed
on Earth). They are almost ubiquitous
(found almost everywhere) including some
of the harshest environments on Earth.
Why are they so successful?
structures such as cell walls made of
peptidoglycan (a glycoprotein unique to
prokaryotes) that maintain cell shape,
provide protections and prevent lysis in
hypotonic environments,
a capsule that protects cells from
dehydration, protects the cells from
chemicals of the immune systems of
hosts, and also helps the cell attach to
surfaces or other cells.
many prokaryotes are capable of motility
mostly by flagella
• mutate rapidly
• periods of exponential population growth
(reproduce by binary fission)
• a great deal of genetic diversity
• Gene transfer
Transformation
Transduction
Conjugation
• Some species produce endospores that
allow the cell to remain dormant when
conditions are not favorable for survival.
Typical structure of a bacillus with a
polar monotrichous flagellum
The existence of all life is dependent on these
organisms
1. All life on the planet evolved from
ancestral bacteria.
2. The early bacteria “prepared” the
environment for future species.
3. Due to their functions in the ecosystems,
all life would cease to exist if they were
eradicated
Some bacteria are important tools
in genetic engineering.
Morphology
Bacteria may exist as single cells, or they
may be filamentous or colonial.
The three most common shapes of bacteria
are:
coccus (plural cocci),
bacillus (plural bacilli),
spirillus (plural spirilla)
Most bacteria have cell walls. The cell walls
of the eubacteria are composed of
peptidoglycan, but the chemical
composition is different from the
archeabacteria.
See table in notes for differences in
the members of the three domains
Genome
1. Bacteria possess about 1/1,000 as much
DNA as eukaryotes.
2. The DNA is concentrated in a nucleoid; it
is circular, and double-stranded.
Metabolic Diversity
1. photoautotrophs utilize light energy and CO2
(e.g., the cyanobacteria)
2. photoheterotrophs utilize light and carbon in
an organic form (restricted to some
prokaryotes)
3. chemoautotrophs utilize CO2 and energy from
the oxidation of inorganic substances (also
called chemosynthetic autotrophs, only in
prokaryotes)
4. chemoheterotrophs obtain energy from
organic compounds (the majority of the
Cyanobacteria
Photoheterotrophs
Chemoautotrophic whale-fall community,
including bacteria mats. (HR)
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Chemoheterotrophs
Domain Archaea.
The oldest living organisms. The extant
species are found in extreme
environments. Unique in that they do not
have peptidoglycan, and have cell
membranes that are different from those of
other living organisms
Taxa include methanogens, thermophiles,
and halophiles.
Thermophiles produce some of the bright colors of
Grand Prismatic Spring, Yellowstone National Park
Methanogens
Domain Bacteria includes
many taxa such as:
Gram positive bacteria
(cocci and bacilli)
The streptococci are those that are arranged in
chains and sometimes in pairs.
The staphylococci are arranged in clusters. They
are faculatively anaerobic and catalase positive. A
medically important species is Staphylococcus
aureus (sepsis, Toxic Shock Syndrome etc.).
The clostridia are spore formers, Gram positive, and bacilli. They are
strict anaerobes often found in soil and are responsible for some
serious diseases such as gangrene (Clostridium perfringens), botulism
(C. botulinum), and tetanus (C. tetani).
Lactic Acid Bacteria are Gram positive organisms that
produce lactic acid as an end product of fermentation.
These catalase negative organisms include the lactobacilli
are non-spore formers that are found in the mouth and the
vagina.
The members of the genus Bacillus are also spore
formers that include free-living forms as well as the
bacterium that causes anthrax (B. anthracis).
The spirochetes (spirally shaped bacteria) are
unique in that they have a flexible cell wall and
axial filaments (for motility).
Chlamydias are unique in that they lack
peptidoglycan and there are two forms in
their life cycle.
Cyanobacteria are photosynthetic
autotrophs that are abundant in marine and
fresh water ecosystems.
Proteobacteria are Gram negative species
that are classified within subgroups.
Some of these are beneficial such as
nitrogen fixing symbiotic species. Others
are harmful such as Rickettsia rickettsia
that causes Rocky Mountain Spotted
Fever.
Rickettsia rickettsia
Important Evolutionary Trends: single cells
to filamentous forms, community
interactions among different species and
compartmentalization of functions within
cells leading to the formation of eukaryotic
cells.