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

Form inside the cells Contain genetic material & enzymes encased in a protective coat

Resistant to extreme conditions Can survive for “extraordinarily” long periods

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 O2 is toxic to some anaerobes

Some can derive energy from organic compounds such as petroleum or benzene

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 Thrive in oxygen-free environments (i.e. a sealed, improperly

sterilized can of food)

Numerous diseases 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”)