Chapter 19 The Diversity of Prokaryotes and Viruses 19 1 Which Organisms Are Members of the Domains Archaea and Bacteria Earth s first organisms were prokaryotes single celled microbes that lacked organelles Prokaryotes are still abundant forming two of life s three domains Bacteria Archaea Bacteria and Archaea are fundamentally different They have a few similarities They are both prokaryotic They are both single celled organisms Differences between Bacteria and Archaea Structural and biochemical features Bacteria and Archaea have different cell walls There are also differences in the plasma membrane composition ribosomes and RNA polymerases between the two domains Differences in transcription and translation processes Features used in prokaryotic classification are Shape Means of locomotion Pigments Nutrient requirements Colony appearance Gram staining characteristics Nucleotide sequences Prokaryotes differ in shape and structure Extremely small Prokaryotes have three common shapes Spherical Rod like Corkscrew shaped Three Common Prokaryote Shapes Fig 19 1 19 2 How Do Prokaryotes Survive and Reproduce Some prokaryotes are motile Flagella are the primary means of locomotion in prokaryotes entire cell surface Flagella are found singly in pairs or scattered over the In bacteria a wheel and axle arrangement anchors the flagellum within the cell wall and plasma membrane enabling the flagellum to rotate rapidly The archaeal flagella are thinner than those of bacteria The Prokaryote Flagellum Fig 19 2 Many bacteria form films on surfaces Some bacteria secrete sticky layers of carbohydrate or protein slime Groups of slime secreting bacteria are called biofilms dental plaque is a biofilm Bacteria embedded in biofilms are protected from disinfectants and antibiotics which is why antibiotics aren t used to kill most bacteria in your mouth Plaque must be physically removed to avoid tooth decay Protective endospores allow some bacteria to withstand adverse conditions Endospores are thickly wrapped particles of genetic material and a few enzymes Endospores form inside some bacteria under inhospitable environmental conditions and get released from the bacterium When a hospitable environment is found metabolism resumes and the endospore develops into a fully functioning bacterium Endospores are resistant even to extremely harsh conditions including boiling for over an hour Endospores found sealed within a rock for 250 million years produced live bacteria when incubated in a test tube Prokaryotes are specialized for specific habitats Each Prokaryotes occupy a wide range of habitats Each prokaryote species is specialized for certain environmental conditions and usually cannot survive outside a narrow range around those conditions Prokaryote habitats High pressure underground environments Cold environments the Antarctic sea ice High salt environments the Dead Sea Acidic or alkaline environments vinegar ammonia Moderate environments the human body Hot environments deep sea vents hot springs Prokaryotes exhibit diverse metabolisms Anaerobic metabolism Some bacteria such as the tetanus bacterium are anaerobes and live without oxygen and are poisoned by it Some bacteria can switch between aerobic and anaerobic respiration For example Escherichia coli in our large intestines Prokaryotes can extract their energy from familiar organic compounds Carbohydrates fats and proteins Or from compounds poisonous to humans Petroleum methane benzene Or from inorganic molecules such as hydrogen sulfur ammonia iron Some bacteria get energy from sunlight Cyanobacteria perform photosynthesis Cyanobacteria Fig 19 6 Prokaryotes reproduce by binary fission Asexual cell division produces identical copies Can occur every 20 minutes A rapid reproductive rate allows for rapid evolution Mutations in DNA are rapidly spread Prokaryotes may exchange genetic material without reproducing Conjugation allows for DNA transfer between Sex pili connect donor to recipient cell by forming donor and recipient a cytoplasmic bridge Conjugation can occur between different species Small circular DNA molecules plasmids carry genes from donor to recipient The plasmids may contain alleles conferring resistance to antibiotics or alleles also found on the main chromosome Conjugation produces new genetic combinations that may allow the resulting bacteria to survive under a greater variety of conditions Conjugation Prokaryotic Mating Fig 19 8 19 3 How Do Prokaryotes Affect Humans and Other Eukaryotes Prokaryotes play important roles in animal nutrition Leaf eating animals e g rabbits cattle depend on digestive tract bacteria to break down cellulose in the cell walls of plants These animals lack the ability to digest cellulose Many human foods are produced by bacterial action e g cheese and yogurt Bacteria in our intestines produce vitamins vitamins K and B12 Prokaryotes are nature s recyclers Many prokaryotes obtain their energy from breaking waste products and the dead bodies of plants and animals into simpler molecules catabolic Decomposition of dead organisms frees nutrients for reuse by new life The recycling of nutrients by prokaryotes and other decomposers provides the basis for continued life on Earth Prokaryotes can clean up pollution Nearly all human made substances are biodegradable by some bacterial species Oil eating bacteria were used in clean up of the Exxon Valdez oil spill disaster of 1989 Some bacteria pose a threat to human health Disease producing bacteria are termed Pathogenic archaea have not been discovered to pathogenic date Some anaerobic bacteria produce dangerous poisons Clostridium tetani causes tetanus It enters the body through a puncture wound If it is lodged deeply enough in the body to avoid oxygen it grows producing a paralyzing poison lockjaw Pathogenic bacteria can cause Bubonic plague Staph infection meningitis food poisoning numerous STDs tuberculosis and many others Humans have battled bacterial diseases throughout history Bubonic plague Black Death Is spread by rat fleas It killed 100 million people in the 1300s roughly a third of the population in some areas compared to AIDS a viral disease which has killed about 30 million Other historical bacterial diseases disappear and then reoccur Tuberculosis once thought to be eliminated from the United States is making a comeback Gonorrhea and syphilis sexually transmitted diseases have reached epidemic proportions around the globe Cholera water transmitted in
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