Chapter 27 Presentation

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  • Figure 27.1 Why is this lakebed red?
  • Figure 27.2 The most common shapes of prokaryotes
  • Figure 27.3 Gram staining
  • Figure 27.3 Gram staining
  • Figure 27.3 Gram staining
  • Figure 27.3 Gram staining
  • Figure 27.4 Capsule
  • Figure 27.5 Fimbriae
  • Figure 27.6 Prokaryotic flagellum
  • Figure 27.6 Prokaryotic flagellum
  • Figure 27.6 Prokaryotic flagellum
  • Figure 27.7 Specialized membranes of prokaryotes
  • Figure 27.7 Specialized membranes of prokaryotes
  • Figure 27.7 Specialized membranes of prokaryotes
  • Figure 27.8 A prokaryotic chromosome and plasmids
  • Figure 27.9 An endospore
  • Figure 27.10 Can prokaryotes evolve rapidly in response to environmental change?
  • Figure 27.10 Can prokaryotes evolve rapidly in response to environmental change?
  • Figure 27.10 Can prokaryotes evolve rapidly in response to environmental change?
  • Figure 27.11 Transduction
  • Figure 27.11 Transduction
  • Figure 27.11 Transduction
  • Figure 27.11 Transduction
  • Figure 27.12 Bacterial conjugation
  • Figure 27.13 Conjugation and recombination in E. coli
  • Figure 27.13a Conjugation and recombination in E. coli
  • Figure 27.13a Conjugation and recombination in E. coli
  • Figure 27.13a Conjugation and recombination in E. coli
  • Figure 27.13b Conjugation and recombination in E. coli
  • Figure 27.13b Conjugation and recombination in E. coli
  • Figure 27.13b Conjugation and recombination in E. coli
  • Table 27-1
  • Figure 27.14 Metabolic cooperation in a colonial prokaryote
  • Figure 27.15 A biofilm
  • Figure 27.16 A simplified phylogeny of prokaryotes
  • Table 27.2
  • Figure 27.17 Extreme thermophiles
  • Figure 27.18 Major groups of bacteria For the Discovery Video Bacteria, go to Animation and Video Files.
  • Figure 27.18 Major groups of bacteria—proteobacteria
  • Figure 27.18 Major groups of bacteria—alpha proteobacteria
  • Figure 27.18 Major groups of bacteria—beta proteobacteria
  • Figure 27.18 Major groups of bacteria—gamma proteobacteria
  • Figure 27.18 Major groups of bacteria—delta proteobacteria
  • Figure 27.18 Major groups of bacteria—delta proteobacteria
  • Figure 27.18 Major groups of bacteria—epsilon proteobacteria
  • Figure 27.18 Major groups of bacteria
  • Figure 27.18 Major groups of bacteria—chlamydias
  • Figure 27.18 Major groups of bacteria—spirochetes
  • Figure 27.18 Major groups of bacteria—cyanobacteria
  • Figure 27.18 Major groups of bacteria—gram-positive bacteria
  • Figure 27.18 Major groups of bacteria—gram-positive bacteria
  • Figure 27.19 Impact of bacteria on soil nutrient availability
  • Figure 27.20 Mutualism: bacterial “headlights”
  • Figure 27.21 Lyme disease For the Discovery Video Antibiotics, go to Animation and Video Files.
  • Figure 27.21 Lyme disease
  • Figure 27.21 Lyme disease
  • Figure 27.21 Lyme disease
  • Figure 27.22 Some applications of prokaryotes For the Discovery Video Tasty Bacteria, go to Animation and Video Files.
  • Figure 27.22 Some applications of prokaryotes
  • Figure 27.22 Some applications of prokaryotes
  • Figure 27.22 Some applications of prokaryotes
  • Chapter 27 Presentation

    1. 1. Chapter 27 Bacteria and Archaea
    2. 2. <ul><li>Prokaryotes thrive almost everywhere, including places too acidic, salty, cold, or hot for most other organisms </li></ul><ul><li>Most prokaryotes are microscopic, but what they lack in size they make up for in numbers </li></ul><ul><li>There are more in a handful of fertile soil than the number of people who have ever lived </li></ul>Overview: Masters of Adaptation
    3. 3. <ul><li>They have an astonishing genetic diversity </li></ul><ul><li>Prokaryotes are divided into two domains: bacteria and archaea </li></ul>Video: Tubeworms
    4. 4. Fig. 27-1
    5. 5. Concept 27.1: Structural and functional adaptations contribute to prokaryotic success <ul><li>Most prokaryotes are unicellular, although some species form colonies </li></ul><ul><li>Most prokaryotic cells are 0.5–5 µ m, much smaller than the 10–100 µ m of many eukaryotic cells </li></ul><ul><li>Prokaryotic cells have a variety of shapes </li></ul><ul><li>The three most common shapes are spheres (cocci), rods (bacilli), and spirals </li></ul>
    6. 6. Fig. 27-2 (a) Spherical (cocci) 1 µm (b) Rod-shaped (bacilli) 2 µm (c) Spiral 5 µm
    7. 7. Cell-Surface Structures <ul><li>An important feature of nearly all prokaryotic cells is their cell wall, which maintains cell shape, provides physical protection, and prevents the cell from bursting in a hypotonic environment </li></ul><ul><li>Eukaryote cell walls are made of cellulose or chitin </li></ul><ul><li>Bacterial cell walls contain peptidoglycan , a network of sugar polymers cross-linked by polypeptides </li></ul>
    8. 8. <ul><li>Archaea contain polysaccharides and proteins but lack peptidoglycan </li></ul><ul><li>Using the Gram stain , scientists classify many bacterial species into Gram-positive and Gram-negative groups based on cell wall composition </li></ul><ul><li>Gram-negative bacteria have less peptidoglycan and an outer membrane that can be toxic, and they are more likely to be antibiotic resistant </li></ul>
    9. 9. <ul><li>Many antibiotics target peptidoglycan and damage bacterial cell walls </li></ul>
    10. 10. Fig. 27-3 Cell wall Peptidoglycan layer Plasma membrane Protein Gram- positive bacteria (a) Gram-positive: peptidoglycan traps crystal violet. Gram- negative bacteria (b) Gram-negative: crystal violet is easily rinsed away, revealing red dye. 20 µm Cell wall Plasma membrane Protein Carbohydrate portion of lipopolysaccharide Outer membrane Peptidoglycan layer
    11. 11. Fig. 27-3a Cell wall Peptidoglycan layer Plasma membrane Protein (a) Gram-positive: peptidoglycan traps crystal violet.
    12. 12. Fig. 27-3b Cell wall Peptidoglycan layer Plasma membrane Protein (b) Gram-negative: crystal violet is easily rinsed away, revealing red dye. Outer membrane Carbohydrate portion of lipopolysaccharide
    13. 13. Fig. 27-3c Gram- positive bacteria Gram- negative bacteria 20 µm
    14. 14. <ul><li>A polysaccharide or protein layer called a capsule covers many prokaryotes </li></ul>
    15. 15. Fig. 27-4 Capsule 200 nm
    16. 16. <ul><li>Some prokaryotes have fimbriae (also called attachment pili ), which allow them to stick to their substrate or other individuals in a colony </li></ul><ul><li>Sex pili are longer than fimbriae and allow prokaryotes to exchange DNA </li></ul>
    17. 17. Fig. 27-5 Fimbriae 200 nm
    18. 18. Motility <ul><li>Most motile bacteria propel themselves by flagella that are structurally and functionally different from eukaryotic flagella </li></ul><ul><li>In a heterogeneous environment, many bacteria exhibit taxis , the ability to move toward or away from certain stimuli </li></ul>Video: Prokaryotic Flagella ( Salmonella typhimurium )
    19. 19. Fig. 27-6 Flagellum Filament Hook Basal apparatus Cell wall Plasma membrane 50 nm
    20. 20. Fig. 27-6a Cell wall Filament Hook Basal apparatus Plasma membrane
    21. 21. Fig. 27-6b Prokaryotic flagellum (TEM) 50 nm
    22. 22. Internal and Genomic Organization <ul><li>Prokaryotic cells usually lack complex compartmentalization </li></ul><ul><li>Some prokaryotes do have specialized membranes that perform metabolic functions </li></ul>
    23. 23. Fig. 27-7 (a) Aerobic prokaryote (b) Photosynthetic prokaryote Thylakoid membranes Respiratory membrane 0.2 µm 1 µm
    24. 24. Fig. 27-7a (a) Aerobic prokaryote Respiratory membrane 0.2 µm
    25. 25. Fig. 27-7b (b) Photosynthetic prokaryote Thylakoid membranes 1 µm
    26. 26. <ul><li>The prokaryotic genome has less DNA than the eukaryotic genome </li></ul><ul><li>Most of the genome consists of a circular chromosome </li></ul><ul><li>Some species of bacteria also have smaller rings of DNA called plasmids </li></ul>
    27. 27. Fig. 27-8 Chromosome Plasmids 1 µm
    28. 28. <ul><li>The typical prokaryotic genome is a ring of DNA that is not surrounded by a membrane and that is located in a nucleoid region </li></ul>
    29. 29. Reproduction and Adaptation <ul><li>Prokaryotes reproduce quickly by binary fission and can divide every 1–3 hours </li></ul><ul><li>Many prokaryotes form metabolically inactive endospores , which can remain viable in harsh conditions for centuries </li></ul>
    30. 30. Fig. 27-9 Endospore 0.3 µm
    31. 31. <ul><li>Prokaryotes can evolve rapidly because of their short generation times </li></ul>
    32. 32. Fig. 27-10 EXPERIMENT RESULTS Daily serial transfer 0.1 mL (population sample) Old tube (discarded after transfer) New tube (9.9 mL growth medium) Fitness relative to ancestor Generation 0 5,000 10,000 15,000 20,000 1.0 1.2 1.4 1.6 1.8
    33. 33. Fig. 27-10a EXPERIMENT Daily serial transfer 0.1 mL (population sample) Old tube (discarded after transfer) New tube (9.9 mL growth medium)
    34. 34. Fig. 27-10b RESULTS Fitness relative to ancestor Generation 0 5,000 10,000 15,000 20,000 1.0 1.2 1.4 1.6 1.8
    35. 35. <ul><li>Prokaryotes have considerable genetic variation </li></ul><ul><li>Three factors contribute to this genetic diversity: </li></ul><ul><ul><li>Rapid reproduction </li></ul></ul><ul><ul><li>Mutation </li></ul></ul><ul><ul><li>Genetic recombination </li></ul></ul>Concept 27.2: Rapid reproduction, mutation, and genetic recombination promote genetic diversity in prokaryotes
    36. 36. Rapid Reproduction and Mutation <ul><li>Prokaryotes reproduce by binary fission, and offspring cells are generally identical </li></ul><ul><li>Mutation rates during binary fission are low, but because of rapid reproduction, mutations can accumulate rapidly in a population </li></ul><ul><li>High diversity from mutations allows for rapid evolution </li></ul>
    37. 37. Genetic Recombination <ul><li>Additional diversity arises from genetic recombination </li></ul><ul><li>Prokaryotic DNA from different individuals can be brought together by transformation, transduction, and conjugation </li></ul>
    38. 38. Transformation and Transduction <ul><li>A prokaryotic cell can take up and incorporate foreign DNA from the surrounding environment in a process called transformation </li></ul><ul><li>Transduction is the movement of genes between bacteria by bacteriophages (viruses that infect bacteria) </li></ul>
    39. 39. Fig. 27-11-1 Donor cell A + B + A + B + Phage DNA
    40. 40. Fig. 27-11-2 A + Donor cell A + B + A + B + Phage DNA
    41. 41. Fig. 27-11-3 Recipient cell B – A + A – Recombination A + Donor cell A + B + A + B + Phage DNA
    42. 42. Fig. 27-11-4 Recombinant cell Recipient cell A + B – B – A + A – Recombination A + Donor cell A + B + A + B + Phage DNA
    43. 43. Conjugation and Plasmids <ul><li>Conjugation is the process where genetic material is transferred between bacterial cells </li></ul><ul><li>Sex pili allow cells to connect and pull together for DNA transfer </li></ul><ul><li>A piece of DNA called the F factor is required for the production of sex pili </li></ul><ul><li>The F factor can exist as a separate plasmid or as DNA within the bacterial chromosome </li></ul>
    44. 44. Fig. 27-12 Sex pilus 1 µm
    45. 45. The F Factor as a Plasmid <ul><li>Cells containing the F plasmid function as DNA donors during conjugation </li></ul><ul><li>Cells without the F factor function as DNA recipients during conjugation </li></ul><ul><li>The F factor is transferable during conjugation </li></ul>
    46. 46. Fig. 27-13 F plasmid F + cell F – cell Mating bridge Bacterial chromosome Bacterial chromosome (a) Conjugation and transfer of an F plasmid F + cell F + cell F – cell (b) Conjugation and transfer of part of an Hfr bacterial chromosome F factor Hfr cell A + A + A + A + A + A – A – A – A – A + Recombinant F – bacterium
    47. 47. Fig. 27-13-1 F plasmid F + cell F – cell Mating bridge Bacterial chromosome Bacterial chromosome (a) Conjugation and transfer of an F plasmid
    48. 48. Fig. 27-13-2 F plasmid F + cell F – cell Mating bridge Bacterial chromosome Bacterial chromosome (a) Conjugation and transfer of an F plasmid
    49. 49. Fig. 27-13-3 F plasmid F + cell F – cell Mating bridge Bacterial chromosome Bacterial chromosome (a) Conjugation and transfer of an F plasmid F + cell F + cell
    50. 50. The F Factor in the Chromosome <ul><li>A cell with the F factor built into its chromosomes functions as a donor during conjugation </li></ul><ul><li>The recipient becomes a recombinant bacterium, with DNA from two different cells </li></ul><ul><li>It is assumed that horizontal gene transfer is also important in archaea </li></ul>
    51. 51. Fig. 27-13-4 F factor Hfr cell (b) Conjugation and transfer of part of an Hfr bacterial chromosome A + A – F – cell A + A + A –
    52. 52. Fig. 27-13-5 F factor Hfr cell (b) Conjugation and transfer of part of an Hfr bacterial chromosome A + A – F – cell A + A + A – A + A + A –
    53. 53. Fig. 27-13-6 F factor Hfr cell (b) Conjugation and transfer of part of an Hfr bacterial chromosome A + A – F – cell A + A + A – A + A + A – Recombinant F – bacterium A – A +
    54. 54. R Plasmids and Antibiotic Resistance <ul><li>R plasmids carry genes for antibiotic resistance </li></ul><ul><li>Antibiotics select for bacteria with genes that are resistant to the antibiotics </li></ul><ul><li>Antibiotic resistant strains of bacteria are becoming more common </li></ul>
    55. 55. Concept 27.3: Diverse nutritional and metabolic adaptations have evolved in prokaryotes <ul><li>Phototrophs obtain energy from light </li></ul><ul><li>Chemotrophs obtain energy from chemicals </li></ul><ul><li>Autotrophs require CO 2 as a carbon source </li></ul><ul><li>Heterotrophs require an organic nutrient to make organic compounds </li></ul><ul><li>These factors can be combined to give the four major modes of nutrition: photoautotrophy, chemoautotrophy, photoheterotrophy, and chemoheterotrophy </li></ul>
    56. 56. Table 27-1
    57. 57. The Role of Oxygen in Metabolism <ul><li>Prokaryotic metabolism varies with respect to O 2 : </li></ul><ul><ul><li>Obligate aerobes require O 2 for cellular respiration </li></ul></ul><ul><ul><li>Obligate anaerobes are poisoned by O 2 and use fermentation or anaerobic respiration </li></ul></ul><ul><ul><li>Facultative anaerobes can survive with or without O 2 </li></ul></ul>
    58. 58. Nitrogen Metabolism <ul><li>Prokaryotes can metabolize nitrogen in a variety of ways </li></ul><ul><li>In nitrogen fixation , some prokaryotes convert atmospheric nitrogen (N 2 ) to ammonia (NH 3 ) </li></ul>
    59. 59. Metabolic Cooperation <ul><li>Cooperation between prokaryotes allows them to use environmental resources they could not use as individual cells </li></ul><ul><li>In the cyanobacterium Anabaena , photosynthetic cells and nitrogen-fixing cells called heterocytes exchange metabolic products </li></ul>Video: Cyanobacteria ( Oscillatoria )
    60. 60. Fig. 27-14 Photosynthetic cells Heterocyte 20 µm
    61. 61. <ul><li>In some prokaryotic species, metabolic cooperation occurs in surface-coating colonies called biofilms </li></ul>
    62. 62. Fig. 27-15 1 µm
    63. 63. Concept 27.4: Molecular systematics is illuminating prokaryotic phylogeny <ul><li>Until the late 20th century, systematists based prokaryotic taxonomy on phenotypic criteria </li></ul><ul><li>Applying molecular systematics to the investigation of prokaryotic phylogeny has produced dramatic results </li></ul>
    64. 64. Lessons from Molecular Systematics <ul><li>Molecular systematics is leading to a phylogenetic classification of prokaryotes </li></ul><ul><li>It allows systematists to identify major new clades </li></ul>
    65. 65. Fig. 27-16 UNIVERSAL ANCESTOR Eukaryotes Korarcheotes Euryarchaeotes Crenarchaeotes Nanoarchaeotes Proteobacteria Chlamydias Spirochetes Cyanobacteria Gram-positive bacteria Domain Eukarya Domain Archaea Domain Bacteria
    66. 66. <ul><li>The use of polymerase chain reaction (PCR) has allowed for more rapid sequencing of prokaryote genomes </li></ul><ul><li>A handful of soil many contain 10,000 prokaryotic species </li></ul><ul><li>Horizontal gene transfer between prokaryotes obscures the root of the tree of life </li></ul>
    67. 67. Archaea <ul><li>Archaea share certain traits with bacteria and other traits with eukaryotes </li></ul>
    68. 68. Fig. 27-UN1 Eukarya Archaea Bacteria
    69. 69. Table 27-2
    70. 70. <ul><li>Some archaea live in extreme environments and are called extremophiles </li></ul><ul><li>Extreme halophiles live in highly saline environments </li></ul><ul><li>Extreme thermophiles thrive in very hot environments </li></ul>
    71. 71. Fig. 27-17
    72. 72. <ul><li>Methanogens live in swamps and marshes and produce methane as a waste product </li></ul><ul><li>Methanogens are strict anaerobes and are poisoned by O 2 </li></ul><ul><li>In recent years, genetic prospecting has revealed many new groups of archaea </li></ul><ul><li>Some of these may offer clues to the early evolution of life on Earth </li></ul>
    73. 73. Bacteria <ul><li>Bacteria include the vast majority of prokaryotes of which most people are aware </li></ul><ul><li>Diverse nutritional types are scattered among the major groups of bacteria </li></ul>
    74. 74. Fig. 27-UN2 Eukarya Archaea Bacteria
    75. 75. Proteobacteria <ul><li>These gram-negative bacteria include photoautotrophs, chemoautotrophs, and heterotrophs </li></ul><ul><li>Some are anaerobic, and others aerobic </li></ul>
    76. 76. Fig. 27-18a Alpha Beta Gamma Delta Epsilon Proteobacteria Subgroup: Beta Proteobacteria Nitrosomonas (colorized TEM) 1 µm Subgroup: Delta Proteobacteria 10 µm Fruiting bodies of Chondromyces crocatus , a myxobacterium (SEM) Bdellovibrio bacteriophorus attacking a larger bacterium (colorized TEM) 5 µm Helicobacter pylori (colorized TEM) 2 µm 0.5 µm Subgroup: Epsilon Proteobacteria B. bacteriophorus Thiomargarita namibiensis containing sulfur wastes (LM) Subgroup: Gamma Proteobacteria Subgroup: Alpha Proteobacteria Rhizobium (arrows) inside a root cell of a legume (TEM) 2.5 µm
    77. 77. Fig. 27-18b Alpha Beta Gamma Delta Epsilon Proteobacteria
    78. 78. Subgroup: Alpha Proteobacteria <ul><li>Many species are closely associated with eukaryotic hosts </li></ul><ul><li>Scientists hypothesize that mitochondria evolved from aerobic alpha proteobacteria through endosymbiosis </li></ul>
    79. 79. <ul><li>Example: Rhizobium , which forms root nodules in legumes and fixes atmospheric N 2 </li></ul><ul><li>Example: Agrobacterium , which produces tumors in plants and is used in genetic engineering </li></ul>
    80. 80. Fig. 27-18c Rhizobium (arrows) inside a root cell of a legume (TEM) 2.5 µm
    81. 81. Subgroup: Beta Proteobacteria <ul><li>Example: the soil bacterium Nitrosomonas , which converts NH 4 + to NO 2 – </li></ul>
    82. 82. Fig. 27-18d Nitrosomonas (colorized TEM) 1 µm
    83. 83. Subgroup: Gamma Proteobacteria <ul><li>Examples include sulfur bacteria such as Chromatium and pathogens such as Legionella , Salmonella , and Vibrio cholerae </li></ul><ul><li>Escherichia coli resides in the intestines of many mammals and is not normally pathogenic </li></ul>
    84. 84. Fig. 27-18e Thiomargarita namibiensis containing sulfur wastes (LM) 0.5 µm
    85. 85. Subgroup: Delta Proteobacteria <ul><li>Example: the slime-secreting myxobacteria </li></ul>
    86. 86. Fig. 27-18f Fruiting bodies of Chondromyces crocatus, a myxobacterium (SEM) 10 µm
    87. 87. Fig. 27-18g Bdellovibrio bacteriophorus attacking a larger bacterium (colorized TEM) 5 µm B. bacteriophorus
    88. 88. Subgroup: Epsilon Proteobacteria <ul><li>This group contains many pathogens including Campylobacter , which causes blood poisoning, and Helicobacter pylori , which causes stomach ulcers </li></ul>
    89. 89. Fig. 27-18h Helicobacter pylori (colorized TEM) 2 µm
    90. 90. Chlamydias <ul><li>These bacteria are parasites that live within animal cells </li></ul><ul><li>Chlamydia trachomatis causes blindness and nongonococcal urethritis by sexual transmission </li></ul>
    91. 91. Fig. 27-18i CHLAMYDIAS 2.5 µm CYANOBACTERIA SPIROCHETES GRAM-POSITIVE BACTERIA Chlamydia (arrows) inside an animal cell (colorized TEM) Leptospira, a spirochete (colorized TEM) 5 µm 50 µm Two species of Oscillatoria, filamentous cyanobacteria (LM ) Streptomyces, the source of many antibiotics (colorized SEM) 5 µm 1 µm Hundreds of mycoplasmas covering a human fibroblast cell (colorized SEM)
    92. 92. Fig. 27-18j 2.5 µm Chlamydia (arrows) inside an animal cell (colorized TEM)
    93. 93. Spirochetes <ul><li>These bacteria are helical heterotrophs </li></ul><ul><li>Some, such as Treponema pallidum , which causes syphilis, and Borrelia burgdorferi , which causes Lyme disease, are parasites </li></ul>
    94. 94. Fig. 27-18k Leptospira, a spirochete (colorized TEM) 5 µm
    95. 95. Cyanobacteria <ul><li>These are photoautotrophs that generate O 2 </li></ul><ul><li>Plant chloroplasts likely evolved from cyanobacteria by the process of endosymbiosis </li></ul>
    96. 96. Fig. 27-18l 50 µm Two species of Oscillatoria, filamentous cyanobacteria (LM )
    97. 97. Gram-Positive Bacteria <ul><li>Gram-positive bacteria include </li></ul><ul><ul><li>Actinomycetes, which decompose soil </li></ul></ul><ul><ul><li>Bacillus anthracis , the cause of anthrax </li></ul></ul><ul><ul><li>Clostridium botulinum , the cause of botulism </li></ul></ul><ul><ul><li>Some Staphylococcus and Streptococcus , which can be pathogenic </li></ul></ul><ul><ul><li>Mycoplasms, the smallest known cells </li></ul></ul>
    98. 98. Fig. 27-18m Streptomyces, the source of many antibiotics (colorized SEM) 5 µm
    99. 99. Fig. 27-18n 1 µm Hundreds of mycoplasmas covering a human fibroblast cell (colorized SEM)
    100. 100. Concept 27.5: Prokaryotes play crucial roles in the biosphere <ul><li>Prokaryotes are so important to the biosphere that if they were to disappear the prospects for any other life surviving would be dim </li></ul>
    101. 101. Chemical Cycling <ul><li>Prokaryotes play a major role in the recycling of chemical elements between the living and nonliving components of ecosystems </li></ul><ul><li>Chemoheterotrophic prokaryotes function as decomposers , breaking down corpses, dead vegetation, and waste products </li></ul><ul><li>Nitrogen-fixing prokaryotes add usable nitrogen to the environment </li></ul>
    102. 102. <ul><li>Prokaryotes can sometimes increase the availability of nitrogen, phosphorus, and potassium for plant growth </li></ul><ul><li>Prokaryotes can also “immobilize” or decrease the availability of nutrients </li></ul>
    103. 103. Fig. 27-19 No bacteria Strain 1 Strain 2 Strain 3 Soil treatment Uptake of K by plants (mg) 0 0.2 0.4 0.6 0.8 1.0
    104. 104. Ecological Interactions <ul><li>Symbiosis is an ecological relationship in which two species live in close contact: a larger host and smaller symbiont </li></ul><ul><li>Prokaryotes often form symbiotic relationships with larger organisms </li></ul>
    105. 105. <ul><li>In mutualism , both symbiotic organisms benefit </li></ul><ul><li>In commensalism , one organism benefits while neither harming nor helping the other in any significant way </li></ul><ul><li>In parasitism , an organism called a parasite harms but does not kill its host </li></ul><ul><li>Parasites that cause disease are called pathogens </li></ul>
    106. 106. Fig. 27-20
    107. 107. Concept 27.6: Prokaryotes have both harmful and beneficial impacts on humans <ul><li>Some prokaryotes are human pathogens, but others have positive interactions with humans </li></ul>
    108. 108. Pathogenic Prokaryotes <ul><li>Prokaryotes cause about half of all human diseases </li></ul><ul><li>Lyme disease is an example </li></ul>
    109. 109. Fig. 27-21 5 µm
    110. 110. Fig. 27-21a Deer tick
    111. 111. 5 µm Fig. 27-21b Borrelia burgdorferi (SEM) 5 µm
    112. 112. Fig. 27-21c Lyme disease rash
    113. 113. <ul><li>Pathogenic prokaryotes typically cause disease by releasing exotoxins or endotoxins </li></ul><ul><li>Exotoxins cause disease even if the prokaryotes that produce them are not present </li></ul><ul><li>Endotoxins are released only when bacteria die and their cell walls break down </li></ul><ul><li>Many pathogenic bacteria are potential weapons of bioterrorism </li></ul>
    114. 114. Prokaryotes in Research and Technology <ul><li>Experiments using prokaryotes have led to important advances in DNA technology </li></ul><ul><li>Prokaryotes are the principal agents in bioremediation , the use of organisms to remove pollutants from the environment </li></ul>
    115. 115. <ul><li>Some other uses of prokaryotes: </li></ul><ul><ul><li>Recovery of metals from ores </li></ul></ul><ul><ul><li>Synthesis of vitamins </li></ul></ul><ul><ul><li>Production of antibiotics, hormones, and other products </li></ul></ul>
    116. 116. Fig. 27-22 (a) (b) (c)
    117. 117. Fig. 27-22a (a)
    118. 118. Fig. 27-22b (b)
    119. 119. Fig. 27-22c (c)
    120. 120. Fig. 27-UN3 Fimbriae Capsule Cell wall Circular chromosome Internal organization Flagella Sex pilus
    121. 121. Fig. 27-UN4
    122. 122. Fig. 27-UN5
    123. 123. You should now be able to: <ul><li>Distinguish between the cell walls of gram-positive and gram-negative bacteria </li></ul><ul><li>State the function of the following features: capsule, fimbriae, sex pilus, nucleoid, plasmid, and endospore </li></ul><ul><li>Explain how R plasmids confer antibiotic resistance on bacteria </li></ul>
    124. 124. <ul><li>Distinguish among the following sets of terms: photoautotrophs, chemoautotrophs, photoheterotrophs, and chemoheterotrophs; obligate aerobe, facultative anaerobe, and obligate anaerobe; mutualism, commensalism, and parasitism; exotoxins and endotoxins </li></ul>

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