Transcript The Diversity of Viruses, Prokaryotes and Protists 2

The Diversity of Viruses, Prokaryotes
and Protists 2: Focus on Prokaryotes
Chapter 19
Prokaryotic Domains
 The Prokaryotes include


Domain Bacteria
Domain Archaea
 Bacteria and Archaea are distinct from
each other microscopically (i.e. cell wall
structure) and biochemically.

Difficult to classify; won’t get into here…
Prokaryotic Domains
 Three common prokaryote shapes
Prokaryotes
 Some prokaryotes
use flagella for
propulsion

“Wheel and axle” type
structure embedded in
plasma membrane and
cell wall
Prokaryotes
 Bacteria often form biofilms


Aggregation of slime-secreting colonies
Often difficult to remove or kill

Example: Dental plaque
Prokaryotes

Protective endospores allow some bacteria to withstand
adverse conditions

Rod-shaped bacteria form endospores




Resistant to extreme conditions
Can survive for “extraordinarily” long periods


Form inside the cells
Contain genetic material & enzymes encased in a protective coat
In one case, 250 million year old endospores were found to be viable!
The bacteria that causes anthrax forms endospores, making them
(unfortunately) ideal for biological weapons.
Prokaryotes
 Most reproduce by fission (simple form of
cell division = asexual)

High reproduction rates (1 division/20 min)


1 cell  1021 cells in a day!
Leads to high mutation rates
•
Unfixed errors during replication  mutation
Prokaryotes
 Some Bacteria and Archaea can exchange genetic
material via conjugation.



Cells temporarily fuse and form cytoplastmic bridge for
movement of DNA between cells
Some bacteria extend “sex pili” to attach to recipient cells
Small, circular DNA called plasmids are transferred
(separate from the main DNA of the cell)
Prokaryotes
 Prokaryotes are specialized
for specific habitats






Around boiling point
(Yellowstone Hotsprings), and
even above boiling point (deep
sea vents at +110ºC)
1.7 miles below Earth’s
surface!
Frozen in ice!
Dead Sea (7 times saltier than
the ocean!)
Dormant in an 11,000 year old
dead Mammoth!
Human bacteria specialize on
certain body regions.
Prokaryotes
 Diverse metabolism

Some are anaerobic; some are aerobic, some
switch between the two


Some can derive energy from organic
compounds such as petroleum or benzene


O2 is toxic to some anaerobes
How could these be useful to humans?
Some can metabolize inorganic molecules
(hydrogen, sulfur, iron, ammonia, nitrite)

Example: Your fish tank!
Prokaryotes
 Diverse metabolism (cont.)

Cyanobacteria are photosynthetic


No chloroplasts; have special chlorophyll-containing membranes
Some deep-sea bacteria are chemosynthetic autotrophs,
using sulfur rather than sunlight for energy (and H2S
rather than H20 for source of hydrogen ions)
Prokaryotes
 Mutualistic relationships

Help plant-eating animals
break down plant material



Cows, rabbits, deer, etc…
Assist in vitamin synthesis
(i.e. vitamin K, B12)
Fix atmospheric nitrogen
needed by plants


In soil and water
Associated with the roots of
legumes (alfalfa, peas and beans,
clover, lupines, etc…)
Prokaryotes
 Impact on human health

Botulism and tetanus attack the nervous system


Numerous diseases





Thrive in oxygen-free environments (i.e. a sealed, improperly
sterilized can of food)
Plague
Lyme disease
Tuberculosis
Cholera
Common bacteria gone bad…

Streptococcus (some strains)
•

“Flesh eating” infection
E. coli (some strains)
Prokaryotes
 Impact on human health


Most bacteria are harmless!
And many are helpful (see “mutualistic
relationships”)