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Chapter 27

Chapter 27. Prokaryotes. Overview: They’re (Almost) Everywhere! Most prokaryotes are microscopic But what they lack in size they more than make up for in numbers The number of prokaryotes in a single handful of fertile soil Is greater than the number of people who have ever lived.

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Chapter 27

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  1. Chapter 27 Prokaryotes

  2. Overview: They’re (Almost) Everywhere! • Most prokaryotes are microscopic • But what they lack in size they more than make up for in numbers • The number of prokaryotes in a single handful of fertile soil • Is greater than the number of people who have ever lived

  3. Figure 27.1 • Prokaryotes thrive almost everywhere • Including places too acidic, too salty, too cold, or too hot for most other organisms

  4. Biologists are discovering • That these organisms have an astonishing genetic diversity

  5. Concept 27.1: Structural, functional, and genetic adaptations contribute to prokaryotic success • Most prokaryotes are unicellular • Although some species form colonies

  6. 2 m 1 m 5 m (a) Spherical (cocci) (c) Spiral (b) Rod-shaped (bacilli) • Prokaryotic cells have a variety of shapes • The three most common of which are spheres (cocci), rods (bacilli), and spirals Figure 27.2a–c

  7. Cell-Surface Structures • One of the most important features 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

  8. Lipopolysaccharide Outer membrane Peptidoglycan layer Cell wall Cell wall Peptidoglycan layer Plasma membrane Plasma membrane Protein Protein Gram- positive bacteria Gram- negative bacteria (a) Gram-positive. Gram-positive bacteria have a cell wall with a large amount of peptidoglycan that traps the violet dye in the cytoplasm. The alcohol rinse does not remove the violet dye, which masks the added red dye. 20 m (b) Gram-negative. Gram-negative bacteria have less peptidoglycan, and it is located in a layer between the plasma membrane and an outer membrane. The violet dye is easily rinsed from the cytoplasm, and the cell appears pink or red after the red dye is added. Figure 27.3a, b • Using a technique called the Gram stain • Scientists can classify many bacterial species into two groups based on cell wall composition, Gram-positive and Gram-negative

  9. 200 nm Capsule Figure 27.4 • The cell wall of many prokaryotes • Is covered by a capsule, a sticky layer of polysaccharide or protein

  10. Fimbriae 200 nm Figure 27.5 • Some prokaryotes have fimbriae and pili • Which allow them to stick to their substrate or other individuals in a colony

  11. Flagellum Filament 50 nm Hook Cell wall Basal apparatus Plasma membrane Figure 27.6 Motility • Most motile bacteria propel themselves by flagella • Which are structurally and functionally different from eukaryotic flagella

  12. In a heterogeneous environment, many bacteria exhibit taxis • The ability to move toward or away from certain stimuli

  13. Internal and Genomic Organization • Prokaryotic cells • Usually lack complex compartmentalization

  14. 0.2 m 1 m Respiratory membrane Thylakoid membranes (a) Aerobic prokaryote (b) Photosynthetic prokaryote Figure 27.7a, b • Some prokaryotes • Do have specialized membranes that perform metabolic functions

  15. Chromosome 1 m Figure 27.8 • The typical prokaryotic genome • Is a ring of DNA that is not surrounded by a membrane and that is located in a nucleoid region

  16. Some species of bacteria • Also have smaller rings of DNA called plasmids

  17. Reproduction and Adaptation • Prokaryotes reproduce quickly by binary fission • And can divide every 1–3 hours

  18. Endospore 0.3 m Figure 27.9 • Many prokaryotes form endospores • Which can remain viable in harsh conditions for centuries

  19. Rapid reproduction and horizontal gene transfer • Facilitate the evolution of prokaryotes to changing environments

  20. Concept 27.2: A great diversity of nutritional and metabolic adaptations have evolved in prokaryotes • Examples of all four models of nutrition are found among prokaryotes • Photoautotrophy • Chemoautotrophy • Photoheterotrophy • Chemoheterotrophy

  21. Major nutritional modes in prokaryotes Table 27.1

  22. Metabolic Relationships to Oxygen • Prokaryotic metabolism • Also varies with respect to oxygen

  23. Obligate aerobes • Require oxygen • Facultative anaerobes • Can survive with or without oxygen • Obligate anaerobes • Are poisoned by oxygen

  24. Nitrogen Metabolism • Prokaryotes can metabolize nitrogen • In a variety of ways • In a process called nitrogen fixation • Some prokaryotes convert atmospheric nitrogen to ammonia

  25. Metabolic Cooperation • Cooperation between prokaryotes • Allows them to use environmental resources they could not use as individual cells

  26. In the cyanobacterium Anabaena • Photosynthetic cells and nitrogen-fixing cells exchange metabolic products Photosynthetic cells Heterocyst 20 m Figure 27.10

  27. 1 m Figure 27.11 • In some prokaryotic species • Metabolic cooperation occurs in surface-coating colonies called biofilms

  28. Concept 27.3: Molecular systematics is illuminating prokaryotic phylogeny • Until the late 20th century • Systematists based prokaryotic taxonomy on phenotypic criteria • Applying molecular systematics to the investigation of prokaryotic phylogeny • Has produced dramatic results

  29. Lessons from Molecular Systematics • Molecular systematics • Is leading to a phylogenetic classification of prokaryotes • Is allowing systematists to identify major new clades

  30. Domain Archaea Domain Eukarya Domain Bacteria Proteobacteria Gram-positive bacteria Nanoarchaeotes Crenarchaeotes Euryarchaeotes Korarchaeotes Cyanobacteria Spirochetes Chlamydias Eukaryotes Gamma Epsilon Alpha Beta Delta Universal ancestor • A tentative phylogeny of some of the major taxa of prokaryotes based on molecular systematics Figure 27.12

  31. Bacteria • Diverse nutritional types • Are scattered among the major groups of bacteria • The two largest groups are • The proteobacteria and the Gram-positive bacteria

  32. Rhizobium (arrows) inside a root cell of a legume (TEM) Nitrosomonas (colorized TEM) Chromatium; the small globules are sulfur wastes (LM) Fruiting bodies of Chondromyces crocatus, a myxobacterium (SEM) Bdellovibrio bacteriophorus Attacking a larger bacterium (colorized TEM) Helicobacter pylori (colorized TEM). • Proteobacteria 2.5 m 1 m 0.5 m Chromatium; the small globules are sulfur wastes (LM) 5 m 10 m Fruiting bodies of Chondromyces crocatus, a myxobacterium (SEM) Bdellovibrio bacteriophorus Attacking a larger bacterium (colorized TEM) 2 m Figure 27.13

  33. Chlamydias, spirochetes, Gram-positive bacteria, and cyanobacteria 2.5 m Chlamydia (arrows) inside an animal cell (colorized TEM) 5 m Leptospira, a spirochete (colorized TEM) 1 m 5 m Hundreds of mycoplasmas covering a human fibroblast cell (colorized SEM) Streptomyces, the source of many antibiotics (colorized SEM) 50 m Two species of Oscillatoria, filamentous cyanobacteria (LM) Figure 27.13

  34. Table 27.2 Archaea • Archaea share certaintraits with bacteria • And other traits with eukaryotes

  35. Some archaea • Live in extreme environments • Extreme thermophiles • Thrive in very hot environments

  36. Figure 27.14 • Extreme halophiles • Live in high saline environments

  37. Methanogens • Live in swamps and marshes • Produce methane as a waste product

  38. Concept 27.4: Prokaryotes play crucial roles in the biosphere • Prokaryotes are so important to the biosphere that if they were to disappear • The prospects for any other life surviving would be dim

  39. Chemical Recycling • Prokaryotes play a major role • In the continual recycling of chemical elements between the living and nonliving components of the environment in ecosystems

  40. Chemoheterotrophic prokaryotes function as decomposers • Breaking down corpses, dead vegetation, and waste products • Nitrogen-fixing prokaryotes • Add usable nitrogen to the environment

  41. Figure 27.15 Symbiotic Relationships • Many prokaryotes • Live with other organisms in symbiotic relationships such as mutualism and commensalism

  42. Other types of prokaryotes • Live inside hosts as parasites

  43. Concept 27.5: Prokaryotes have both harmful and beneficial impacts on humans • Some prokaryotes are human pathogens • But many others have positive interactions with humans

  44. 5 µm Figure 27.16 Pathogenic Prokaryotes • Prokaryotes cause about half of all human diseases • Lyme disease is an example

  45. Pathogenic prokaryotes typically cause disease • By releasing exotoxins or endotoxins • Many pathogenic bacteria • Are potential weapons of bioterrorism

  46. Prokaryotes in Research and Technology • Experiments using prokaryotes • Have led to important advances in DNA technology

  47. Figure 27.17 • Prokaryotes are the principal agents in bioremediation • The use of organisms to remove pollutants from the environment

  48. Prokaryotes are also major tools in • Mining • The synthesis of vitamins • Production of antibiotics, hormones, and other products

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