Prokaryotic diversity
Major points
• Prokaryotes are incredibly diverse
• Life on earth started with prokaryotes
• Life on earth depends on prokaryotes
Reading (2)
Chapter 27
(Campbell et al., BIOLOGY, 5th ed.)
Prokaryotic diversity
I. Prokaryotes
A. Definition
B. Phylogeny (evolutionary history)
II. Structural diversity
III. Nutritional and metabolic diversity
IV. Ecological diversity
What is a prokaryote?
What is a bacterium?
Prokaryotes
• Cells that lack a membrane-enclosed
nucleus and organelles
• Include two of the three domains of life
– Bacteria
– Archaea
Three domains of life
Comparison: three domains of life
What conclusions can you make about the
evolutionary relationship between the
three domains of life (Bacteria, Archaea,
and Eukarya)?
Phylogeny (evolutionary history)
• Organisms have been evolving in three
independent lineages
• Eukarya and Archaea share a common
ancestor that lived more recently than the
ancestor common to Archaea and Bacteria
History
of life
Evolutionary history of
prokaryotes
• ~3.8 billion years old
• Originated within only a few 100 million
years after Earth cooling
• Archaea and Bacteria diverged 2-3 billion
years ago (about when O2 accumulated)
• No eukaryotes for ~2 billion years
Prokaryotic diversity
I. Prokaryotes
II. Structural diversity
A. Phylogeny
B. Cell structure
III. Nutritional and metabolic diversity
IV. Ecological diversity
Phylogeny of prokaryotes
Phylogeny
• Bacteria: 12 “kingdom”-like groups
(5 shown)
• Archaea: three “kingdom”-like groups
Archaea
• Methanogens
Produce methane
• Extreme halophiles
Live in high salt
• Extreme thermophiles
Live at high temperatures
Likely closest relative to eukaryotes
Cell structure
• Three common shapes
– Spheres (cocci)
– Rods (bacilli)
– Helices
• Size is about 1 to 5 µm
(but largest is 0.5 mm!)
• Most have cell wall (protection and shape)
• Many have flagella (movement)
Cell wall
• Found in all prokaryotes except
mycoplasma
• Protects cell and defines shape
• Bacterial cell wall composed of
peptidoglycan
• Different structure than eukaryotic cell
walls (found in plants and fungi)
Cell wall structure
Flagella
• Movement
• Different
structure and
mechanism than
eukaryotic
flagella
Prokaryotic diversity
I. Prokaryotes
II. Structural diversity
III. Nutritional and metabolic diversity
A. Energy and carbon acquisition
B. Nitrogen metabolism
C. Oxygen response
IV. Ecological diversity
Energy and carbon acquisition
• Organisms can be classified based on how
they acquire energy and carbon
• Energy is either from light (phototroph) or
chemicals (chemotroph)
• Carbon is either from inorganic CO2
(autotroph) or from organic molecule
(heterotroph)
• Four combinations (all found in prokaryotes)
Major nutritional modes
• Photoautotroph
light for energy and CO2 for carbon
(photosynthetic)
• Chemoautotroph
chemicals (H2S, NH3, etc.) for energy and CO2
• Photoheterotroph
light for energy and organic molecules for carbon
• Chemoheterotroph
organic molecules for both energy and carbon
Cyanobacteria
• Photoautotroph (photosynthetic)
• Changed the world (~2.5 billion years ago)
by making O2!
Nitrogen metabolism
• Nitrogen is an essential ingredient of life
• We (animals and plants) can only use
nitrogen in certain chemical forms
• Prokaryotes are critically important in
nitrogen cycling
• Nitrogen fixation (N2 -> NH3) is catalyzed
only by prokaryotes (including Rhizobium
that lives symbiotically in roots of legumes)
Oxygen responses
• Obligate aerobes: use and require oxygen
• Facultative anaerobes: can use oxygen if
available but do not need it for growth
• Obligate anaerobes: killed by oxygen
Prokaryotic diversity
I. Prokaryotes
II. Structural diversity
III. Nutritional and metabolic diversity
IV. Ecological diversity
A. Environmental roles
B. Symbiosis
Environmental roles
• Essential role in cycling of nutrients
• Extract nutrients, including nitrogen, from
nonliving world for use by living organisms
• Decompose waste products and dead
organisms, returning nutrients for use
Life on earth depends on the diverse
metabolic activity of prokaryotes
Human uses
• Breakdown oil and other chemicals that
have been spilled
• Industrial syntheses of certain chemicals,
including antibiotics
• Yogurt and cheese production
• Biotechnology
Symbiosis
• Ecological relationship between organisms
of two different species that live together in
close contact
• Three types:
– Mutualism: both organisms benefit (Rhizopium
and legumes)
– Commensulism: one organsim benefits and the
other does not mind
– Parasitism: one organism (parasite) benefits by
hurting the other (host)
Bio103 home