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  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  O 2 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 H 2 S rather than H 2 0 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, B 12 ) 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”)