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Bacteria and Archaea: Masters of Adaptation

This chapter provides an overview of the structural and functional adaptations of prokaryotes, including their cell-surface structures, motility, rapid reproduction and mutation, nitrogen metabolism, chemical recycling, ecological interactions, and both harmful and beneficial impacts.

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Bacteria and Archaea: Masters of Adaptation

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  1. Chapter 27 Bacteria and Archaea Please review: Introduction Cell-surface structures Motility Rapid reproduction and mutation Nitrogen metabolism Archaea Chemical recycling Ecological interactions Prokaryotes have both harmful and beneficial impacts

  2. Overview: Masters of Adaptation • Prokaryotes thrive almost everywhere, including places too acidic, salty, cold, or hot for most other organisms • Most prokaryotes are microscopic, but what they lack in size they make up for in numbers • There are more in a handful of fertile soil than the number of people who have ever lived

  3. They have an astonishing genetic diversity • Prokaryotes are divided into two domains: bacteria and archaea

  4. Fig. 27-1

  5. Concept 27.1: Structural and functional adaptations contribute to prokaryotic success • Most prokaryotes are unicellular, although some species form colonies • Most prokaryotic cells are 0.5–5 µm, much smaller than the 10–100 µm of many eukaryotic cells • Prokaryotic cells have a variety of shapes • The three most common shapes are spheres (cocci), rods (bacilli), and spirals

  6. Fig. 27-2 2 µm 5 µm 1 µm (a) Spherical (cocci) (b) Rod-shaped (bacilli) (c) Spiral

  7. Cell-Surface Structures • 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 • Eukaryote cell walls are made of cellulose or chitin • Bacterial cell walls contain peptidoglycan, a network of sugar polymers cross-linked by polypeptides

  8. Archaea contain polysaccharides and proteins but lack peptidoglycan • Using the Gram stain, scientists classify many bacterial species into Gram-positive and Gram-negative groups based on cell wall composition • Gram-negative bacteria have less peptidoglycan and an outer membrane that can be toxic, and they are more likely to be antibiotic resistant

  9. Many antibiotics target peptidoglycan and damage bacterial cell walls

  10. Fig. 27-3 Carbohydrate portion of lipopolysaccharide Outer membrane Peptidoglycan layer Cell wall Cell wall Peptidoglycan layer Plasma membrane Plasma membrane Protein Protein Gram- positive bacteria Gram- negative bacteria 20 µm (b) Gram-negative: crystal violet is easily rinsed away, revealing red dye. (a) Gram-positive: peptidoglycan traps crystal violet.

  11. Fig. 27-3a Peptidoglycan layer Cell wall Plasma membrane Protein (a) Gram-positive: peptidoglycan traps crystal violet.

  12. Fig. 27-3b Carbohydrate portion of lipopolysaccharide Outer membrane Cell wall Peptidoglycan layer Plasma membrane Protein (b) Gram-negative: crystal violet is easily rinsed away, revealing red dye.

  13. Fig. 27-3c Gram- positive bacteria Gram- negative bacteria 20 µm

  14. A polysaccharide or protein layer called a capsule covers many prokaryotes Quorum sensing is a system of stimulae and response correlated to population density. Many species of bacteria use quorum sensing to coordinate gene expression according to the density of their local population. Identified by Dr. Bonnie Bassler – Princeton University https://www.youtube.com/watch?v=SWgfSELnzog https://www.youtube.com/watch?v=FsGwgiIv_NU Bozeman Video

  15. For gene transcription to be activated, the cell must encounter signaling molecules secreted by other cells in its environment. When only a few other bacteria of the same kind are in the vicinity, diffusion reduces the concentration of the inducer in the surrounding medium to almost zero, so the bacteria produce little inducer. However, as the population grows, the concentration of the inducer passes a threshold, causing more inducer to be synthesized. This forms a positive feedback loop, and the receptor becomes fully activated. Activation of the receptor induces the up- regulation of other specific genes, causing all of the cells to begin transcription at approximately the same time. This coordinated behavior of bacterial cells can be useful in a variety of situations. For instance, the bioluminescent luciferase produced by Vibrio fischeri would not be visible if it were produced by a single cell. By using quorum sensing to limit the production of luciferase to situations when cell populations are large, V. fischeri cells are able to avoid wasting energy on the production of useless product. http://en.wikipedia.org/wiki/Quorum_sensing

  16. Fig. 27-4 200 nm Capsule

  17. Some prokaryotes have fimbriae (also called attachment pili), which allow them to stick to their substrate or other individuals in a colony • Sex pili are longer than fimbriae and allow prokaryotes to exchange DNA

  18. Fig. 27-5 Fimbriae 200 nm

  19. Motility • Most motile bacteria propel themselves by flagella that are structurally and functionally different from eukaryotic flagella • In a heterogeneous environment, many bacteria exhibit taxis, the ability to move toward or away from certain stimuli Video: Prokaryotic Flagella (Salmonella typhimurium)

  20. Fig. 27-6 Flagellum Filament 50 nm Cell wall Hook Basal apparatus Plasma membrane

  21. Fig. 27-6a Filament Cell wall Hook Basal apparatus Plasma membrane

  22. Fig. 27-6b 50 nm Prokaryotic flagellum (TEM)

  23. Internal and Genomic Organization • Prokaryotic cells usually lack complex compartmentalization • Some prokaryotes do have specialized membranes that perform metabolic functions

  24. Fig. 27-7 1 µm 0.2 µm Respiratory membrane Thylakoid membranes (a) Aerobic prokaryote (b) Photosynthetic prokaryote

  25. Fig. 27-7a 0.2 µm Respiratory membrane (a) Aerobic prokaryote

  26. Fig. 27-7b 1 µm Thylakoid membranes (b) Photosynthetic prokaryote

  27. The prokaryotic genome has less DNA than the eukaryotic genome • Most of the genome consists of a circular chromosome • Some species of bacteria also have smaller rings of DNA called plasmids

  28. Fig. 27-8 Chromosome Plasmids 1 µm

  29. The typical prokaryotic genome is a ring of DNA that is not surrounded by a membrane and that is located in a nucleoid region

  30. Reproduction and Adaptation • Prokaryotes reproduce quickly by binary fission and can divide every 1–3 hours • Many prokaryotes form metabolically inactive endospores, which can remain viable in harsh conditions for centuries

  31. Fig. 27-9 Endospore 0.3 µm

  32. Prokaryotes can evolve rapidly because of their short generation times

  33. Fig. 27-10 EXPERIMENT Daily serial transfer 0.1 mL (population sample) New tube (9.9 mL growth medium) Old tube (discarded after transfer) RESULTS 1.8 1.6 Fitness relative to ancestor 1.4 1.2 1.0 10,000 0 5,000 15,000 20,000 Generation

  34. Fig. 27-10a EXPERIMENT Daily serial transfer 0.1 mL (population sample) Old tube (discarded after transfer) New tube (9.9 mL growth medium)

  35. Fig. 27-10b RESULTS 1.8 1.6 Fitness relative to ancestor 1.4 1.2 1.0 20,000 10,000 0 5,000 15,000 Generation

  36. Concept 27.2: Rapid reproduction, mutation, and genetic recombination promote genetic diversity in prokaryotes • Prokaryotes have considerable genetic variation • Three factors contribute to this genetic diversity: • Rapid reproduction • Mutation • Genetic recombination

  37. Rapid Reproduction and Mutation • Prokaryotes reproduce by binary fission, and offspring cells are generally identical • Mutation rates during binary fission are low, but because of rapid reproduction, mutations can accumulate rapidly in a population • High diversity from mutations allows for rapid evolution

  38. Genetic Recombination • Additional diversity arises from genetic recombination • Prokaryotic DNA from different individuals can be brought together by transformation, transduction, and conjugation

  39. Transformation and Transduction • A prokaryotic cell can take up and incorporate foreign DNA from the surrounding environment in a process called transformation • Transduction is the movement of genes between bacteria by bacteriophages (viruses that infect bacteria)

  40. Fig. 27-11-1 Phage DNA A+ B+ A+ B+ Donor cell

  41. Fig. 27-11-2 Phage DNA A+ B+ A+ B+ Donor cell A+

  42. Fig. 27-11-3 Phage DNA A+ B+ A+ B+ Donor cell A+ Recombination A+ A– B– Recipient cell

  43. Fig. 27-11-4 Phage DNA A+ B+ A+ B+ Donor cell A+ Recombination A+ A– B– Recipient cell A+ B– Recombinant cell

  44. Conjugation and Plasmids • Conjugation is the process where genetic material is transferred between bacterial cells • Sex pili allow cells to connect and pull together for DNA transfer • A piece of DNA called the F factor is required for the production of sex pili • The F factor can exist as a separate plasmid or as DNA within the bacterial chromosome

  45. Fig. 27-12 1 µm Sex pilus

  46. The F Factor as a Plasmid • Cells containing the F plasmid function as DNA donors during conjugation • Cells without the F factor function as DNA recipients during conjugation • The F factor is transferable during conjugation

  47. Fig. 27-13 F plasmid Bacterial chromosome F+ cell F+ cell Mating bridge F– cell F+ cell Bacterial chromosome (a) Conjugation and transfer of an F plasmid Recombinant F– bacterium A+ Hfr cell A+ A+ A+ F factor A– A+ A– A+ A– A– F– cell (b) Conjugation and transfer of part of an Hfr bacterial chromosome

  48. Fig. 27-13-1 Bacterial chromosome F plasmid F+ cell Mating bridge F– cell Bacterial chromosome (a) Conjugation and transfer of an F plasmid

  49. Fig. 27-13-2 Bacterial chromosome F plasmid F+ cell Mating bridge F– cell Bacterial chromosome (a) Conjugation and transfer of an F plasmid

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