Bio1151 Chapter 27 Bacteria and Archaea
  1. Most prokaryotes are microscopic, and can be found almost anywhere. The most common shapes are          (cocci),       (bacilli), and          .

      The tree of life. Based on rRNA gene sequences, living organisms are divided into 3 domains: Bacteria, Archaea, and Eukarya. Eukarya and Archaea appear to share a common ancestor, are more closely related to each other than to Bacteria. Note: Archaea and Bacteria are "prokaryotes" that lack organelles such as a nucleus. The lack of organelles is not a shared derived character, thus "prokaryotes" do not constitute a clade.


      Cocci (singular, coccus) are spherical prokaryotes. They occur singly, in pairs (diplococci), in chains (such as these streptococci), and in clusters like bunches of grapes (staphylococci). Bacilli (singular, bacillus) are rod-shaped prokaryotes. They are usually solitary, sometimes the rods are arranged in chains (streptobacilli). Spiral prokaryotes include spirilla, which range from comma-like shapes to long coils, and spirochetes (shown here), which are corkscrew-shaped.


      Staphylococcus toxins are a common cause of food poisoning; the enterotoxins are heat resistant and can survive boiling for several minutes. Staphylococcus aureus can infect wounds. Staphylococcus_aureus.jpg,710,536-->
     
     
     
     
  2. Many bacteria exhibit        , the directional movement in response to a           , by propelling themselves with           .

      Prokaryotic flagellum. Unlike an eukaryote flagellum, the motor of the prokaryotic flagellum is a basal apparatus embedded in the plasma membrane. A curved hook turns in the basal apparatus, moving the attached filament, which is composed of the protein flagellin. This allows the cell to responding to a stimulus in a directional movement called taxis.
     
     
     
     
  3. The prokaryotic genome is usually a circular ring of DNA located in a           region; some also have smaller rings of DNA called           .

      A prokaryote such as this E. coli cell has a circular chromosome consisting of a single ring of DNA, located in a nucleoid region. Many cells also harbor smaller, non-genome rings of DNA called plasmids.
     
     
     
     
  4. Prokaryotic cells lack             . The cell wall of many prokaryotes is covered by a protective          , and many also form             in harsh conditions. Review.

      Specialized membranes of prokaryotes. Infoldings of the plasma membrane, reminiscent of the cristae of mitochondria, function in cellular respiration in some aerobic prokaryotes. Photosynthetic prokaryotes called cyanobacteria have thylakoid membranes, much like those in chloroplasts.


      The polysaccharide or protein capsule surrounding the cell wall of this Streptococcus enables the bacterium to attach to cells that line the human respiratory tract, such as a tonsil cell. Other prokaryotes stick to the substrate by fimbriae.


      Some prokaryotes attach to surfaces or to other prokaryotes via numerous protein appendages called fimbriae. 27_05ProkFimbriae.jpg,538,321-->


      An endospore. Bacillus anthracis, the bacterium that causes anthrax, produces persistent endospores. An endospore's thick, protective coat helps it survive in the soil for years.
     
     
     
     
  5. Response to       stain classified bacterial species into two groups based on amount of                in the cell       : gram-           and gram-           .

      Bacteria are stained with a violet dye and iodine, rinsed in alcohol, and then stained with a red dye. Gram-positive bacteria have a cell wall with a large amount of peptidoglycan that traps the violet dye in the cytoplasm, masking the added red dye. Gram-negative bacteria have less peptidoglycan. The violet dye is easily rinsed from the cytoplasm, and the cell appears red after the red dye is added.
     
     
     
     
  6. Molecular analysis has now revealed several         among the gram–negative prokaryotes, while another group is now assigned its own domain of          .

      Prokaryotes do not constitute a monophyletic clade. Archaea are more closely related to Eukarya than to Bacteria.


      A cladogram is used to track relationships by shared derived characters inherited from a common ancestor. Clades are defined by an evolutionary novelty at the branching point, which constitues a shared derived character (homology) for the clade (ingroup). An outgroup does not possess that character. 26_11bCharTablePhylTreeB-L.jpg,720,544-->


      A comparison of the three domains of life. Among the prokaryotes, Aside from not having organelles such as the nucleus, and having circular DNA, Archaea exhibit many traits not shared with Bacteria.
     
     
     
     
    • Many archaea live in extreme conditions:               thrive in hot environments,             live in saline environments, and              live in swamps.

        Extreme thermophiles. Orange and yellow colonies of heatloving archaea in the hot water of a Nevada geyser.


        Extreme halophiles. Colorful saltloving archaea thrive in these ponds near San Francisco. Used for commercial salt production, the ponds contain water that is five to six times as salty as seawater.


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    • The gram-           bacteria constitute their own clade.

        Gram-Positive Bacteria Soil-dwelling Streptomyces are a source of many antibiotics, including streptomycin used to treat tuberculosis, which is caused by another gram-positive bacteriun, Mycobacterium tuberculosis Mycoplasmas are tiny and have no cell walls. One species causes "walking pneumonia". Hundreds of mycoplasmas are seen here covering a human fibroblast cell.
       
       
       
       
    • Gram-           bacteria include cyanobacteria, and                 , which includes E. coli and the nitrogen fixing Rhizobium.


      Cyanobacteria ("Blue-green algae") are photosynthetic and can form stromatolites. These two species of Oscillatoria form a filamentous colony. Some filamentous colonies such as Anabaena have cells specialized for nitrogen fixation.


      Sedimentary rocks are deposited into strata, with the older fossils buried in deeper layers. Some of the earliest fossils (3.5 billion years old) are stromatolites formed when layers of sediment were trapped by bacteria. Dimetrodon was an early tetrapod adapted for terrestrial life. 25_04-FossilTimeline0-L.jpg,532,600-->


      Metabolic cooperation in a colonial prokaryote. In the filamentous cyanobacterium Anabaena, cells known as heterocytes fix nitrogen, while the other cells carry out photosynthesis, and these cells exchange metabolic products. 27_10Anabena.jpg,888,420-->


      Escherichia coli is a proteobacterium in the Gram-negative group.


      Rhizobium is another proteobacterium among the Gram-negative bacteria. They live inside root cells of legumes (plants of the pea/bean family), where the bacteria convert atmospheric nitrogen to organic compounds such as ammonia in a process called nitrogen fixation.
     
     
     
     
  7. Prokaryotes play crucial roles in the biosphere.
     
     
     
     
    • Most are              and recycle nutrients in the ecosystem.
       
       
       
       
    • Some are nitrogen         and convert atmospheric           (N2) to an organic form such as          (NH3) that can be used by other organisms.

        Rhizobium is another proteobacterium among the Gram-negative bacteria. They live inside root cells of legumes (plants of the pea/bean family), where the bacteria convert atmospheric nitrogen to organic compounds such as ammonia in a process called nitrogen fixation.
       
       
       
       
    • Cyanobacteria are            and release oxygen for aerobic organisms to use.

        Cyanobacteria ("Blue-green algae") are photosynthetic and can form stromatolites. These two species of Oscillatoria form a filamentous colony. Some filamentous colonies such as Anabaena have cells specialized for nitrogen fixation.


        Sedimentary rocks are deposited into strata, with the older fossils buried in deeper layers. Some of the earliest fossils (3.5 billion years old) are stromatolites formed when layers of sediment were trapped by bacteria. Dimetrodon was an early tetrapod adapted for terrestrial life. 25_04-FossilTimeline0-L.jpg,532,600-->


        Metabolic cooperation in a colonial prokaryote. In the filamentous cyanobacterium Anabaena, cells known as heterocytes fix nitrogen, while the other cells carry out photosynthesis, and these cells exchange metabolic products. 27_10Anabena.jpg,888,420-->
       
       
       
       
    • In the cyanobacterium Anabaena,                 cells and           -fixing cells exchange metabolic products in a cooperative         .


      Metabolic cooperation in a colonial prokaryote. In the filamentous cyanobacterium Anabaena, cells known as heterocytes fix nitrogen, while the other cells carry out photosynthesis, and these cells exchange metabolic products.
     
     
     
     
  8. Some prokaryotes are human pathogens, such as the             bacterium that causes Lyme disease. Pathogenic prokaryotes release two types of         .

      Lyme disease. Ticks in the genus Ixodes spread the disease by transmitting the spirochete Borrelia burgdorferi. A large, ringshaped rash may develop at the site of the tick's bite.
     
     
     
     
    •            are secreted           , such as those that cause anthrax and cholera.
       
       
       
       
    •             are lipopolysaccharide components of bacterial            and released only when the bacteria such as Salmonella      .