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Chapter 27 Prokaryotes and the Origins of Metabolic Diversity Slide 2 I. The world of prokaryotes A. Theyre everywhere! 1. Collective prokaryote biomass outweighs all eukaryotes combined by at least tenfold. 2. They exist almost everywhere, including places where eukaryotes cannot. Slide 3 Slide 4 3. Most prokaryotes are beneficial; we couldnt live without them. (e.g. Nitrogen-fixing bacteria) 4. Some cause illness bubonic plague, diphtheria, salmonella 5. Approximately 5000 species have been identified. Estimates of prokaryote diversity range from 400,000 to 4,000,000 species. B. Bacteria and archaea are the two main branches of prokaryote evolution 1. Archaea are thought to be more closely related to eukaryotes than to bacteria. Slide 5 Slide 6 II. Structure, function, and reproduction of prokaryotes A. Most prokaryotes are unicellular. 1. Some species form aggregates of two or more individuals. B. Three (3) common shapes: cocci (round); bacilli (rod); helical (spiral) Slide 7 Slide 8 C. Prokaryotes are typically 1-5 m in diameter, but some can be seen by the naked eye. - Eukaryotic cells are typically 10-100 m in diameter. Slide 9 Slide 10 Slide 11 D. Almost all prokaryotes have cell walls external to the plasma membrane. 1. Cell walls maintain cell shape. 2. Cell walls are composed of peptidoglycan. Slide 12 3. There are two types of cell walls. Bacteria are grouped according to cell wall type. a. Gram-positive bacteria have simple, thick cell walls. Their cell walls are composed of a relatively large amount of peptidoglycan. b. Gram-negative bacteria have less peptidoglycan and are more complex. They have a peptidoglycan layer surrounded by the plasma membrane and an outer membrane. - Gram-negative bacteria are typically more resistant to host immune defenses and antibiotics. Note that the two types of bacteria can be stained to determine which is gram-negative (pink) and gram-positive (purple) using a Gram Stain. Slide 13 Slide 14 Peptidoglycan Gram Positive Gram Negative Plasma membrane Outer membrane Lipopolysaccharide layer Slide 15 Slide 16 4. Most prokaryotes secrete sticky substances that form a protective layer and enable them to adhere to substrates. a. The sticky protective layer secreted by prokaryotes is called the capsule. 5. Some prokaryotes adhere to substrates using pili. a. Some pili are specialized for DNA transfer. This process is called conjugation; note for later in class. Slide 17 Slide 18 E. Many prokaryotes are motile - Some exceed speeds 100 times their body length per second. 1. Modes of movement Note the three types: a. Flagellum - basal apparatus rotates the flagellum and propels the cell b. Corkscrew movement of spirochetes (helical) c. Some prokaryotes glide over jets of slimy secretions. 2. Many prokaryotes move toward or away from a stimulus = taxis. Chemotaxis is the movement toward or away from a chemical. Slide 19 Slide 20 Slide 21 Slide 22 Slide 23 F. Cellular and genomic organization of prokaryotes is different from that of eukaryotes 1. Prokaryotes have no nucleus. 2. The nucleoid region in a prokaryotic cell consists of a concentrated mass of DNA. This mass of DNA is usually one thousand times less than what is found in a eukaryote. 3. A prokaryote may have a plasmid in addition to its major chromosome. A plasmid is a small ring of DNA that carries accessory genes. Usually these genes are for antibiotic resistance! Slide 24 Asexual reproduction: Fission Slide 25 Specialized membranes of prokaryotes Slide 26 G. Prokaryotes grow and adapt rapidly - The doubling time for E. coli is 20 minutes. Start with one E. coli cell. After 48 hours of doubling every 20 minutes, the mass of E. coli would be 10,000 times the mass of the earth. Bacteria do not have gene transfer by sexual reproduction, but do transfer genes. Why? This is an aid in adapting (evolving). 1. Three (3) ways for genes to be transferred between cells: a. Transformation cell takes up genes from the surrounding environment. b. Conjugation direct transfer of genes from one prokaryote to another. Use the sex pilus to conjugate. c. Transduction viruses transfer genes between prokaryotes. Slide 27 Prokaryotic conjugation Slide 28 Bacterial transduction Slide 29 2. Endospores are resistant cells formed by some bacteria as a way to withstand harsh conditions. The cell replicates its chromosome and wraps it in a durable wall that can protect the chromosome from adverse conditions, e.g. boiling water, desiccation. When the environment is good again, the cell will revive to a new vegetative (growing) spore. Slide 30 Slide 31 Slide 32 III. Nutritional and metabolic diversity A. All prokaryotes (and eukaryotes too) are grouped into four (4) categories according to how they obtain energy and carbon. 1. Photoautotrophs - Photosynthetic use light as the energy source - CO 2 is the carbon source Example: Cyanobacteria; plants (eukaryotic). Slide 33 One of the most independent organisms on earth: Cyanobacteria (Anabaena) Slide 34 Cyanobacteria: Gloeothece ( top left), Nostoc (top right), Calothrix (bottom left), Fischerella (bottom right) Slide 35 A bloom of cyanobacteria Slide 36 Algal blooms Anabaena Microcystis Slide 37 2. Chemoautotrophs - Energy from oxidation of inorganic substances (e.g. NH 4, and S) - CO 2 is the carbon source Example: Sulfolobus, Beggiatoa (shown on slide) Slide 38 Slide 39 3. Photoheterotrophs - Light as energy source - Organic compounds are source of carbon 4. Chemoheterotrophs - Organic compounds are energy source and source of carbon (this includes humans) Examples: Many prokaryotes; animals (eukaryotic); fungi (eukaryotic) Slide 40 Slide 41 Slide 42 Slide 43 B. Metabolic relationships to oxygen 1. Obligate aerobes - Use O 2 for respiration; cannot grow without it. (Humans are obligate aerobes) 2. Facultative aerobes - Use O 2 when available; ferment when O 2 isnt available. 3. Obligate anaerobes - Poisoned by O 2 ; use fermentation or live by anaerobic respiration. In anaerobic respiration, inorganic molecules like SO 4, NO 3, and Fe 3+ are used instead of oxygen. Slide 44 C. Photosynthesis evolved early in prokaryotic life 1. Cyanobacteria started to produce O 2 about 2.7 billion years ago Contrasting hypotheses for the taxonomic distribution of photosynthesis among prokaryotes. Slide 45 Slide 46 Slide 47 Slide 48 A. Great diversity of Archaea in extreme environments and oceans 1. Two taxa of archae: a. Euryarchaeota most archae b. Crenarcheota most thermophilic species 2. Examples of extremophiles a. Methanogens produce methane - Energy is from hydrogen gas - Strictly anaerobic - Inhabit swamps and animal intestines b. Extreme halophiles - Live in salty environments (Great Salt Lake) Slide 49 Slide 50 c. Extreme thermophiles - 60- 80 C optimum temperatures (hot springs) - 105 C for deep-sea hydrothermal vents Slide 51 Slide 52 Slide 53 Rhizobium: N 2 -Fixing, Lives in Plant Roots of Legumes Slide 54 Chromatium: Example of a chemoautotroph; Note the sulfur granules Slide 55 Bdellovibrio: Bacterial predator Slide 56 Myxobacterium: Produces cell aggregates and fruiting bodies Slide 57 Heliobacter: Causes stomach ulcers Slide 58 The remaining four clades and examples for each are: Slide 59 2. Chlamydias - Parasitic; survive only within cells of animals - Some cause STDs e.g. chlamydia Slide 60 3. Spirochetes - Helical heterotrophs - Some cause STDs e.g. syphilis Slide 61 4. Gram-Positive Bacteria - Broad, diverse group - Antibiotic producing bacteria are in this group - Example shown is Streptomyces (streptomycin) - And (next slide) Slide 62 Mycoplasma shown covering a human cell; some species of mycoplasmas cause walking pneumonia Slide 63 5. Cyanobacteria - Oxygenic photosynthesis, and chloroplasts evolved from them. Slide 64 V. Ecological impacts of prokaryotes A. Prokaryotes are links in the recycling of chemical elements B. Many prokaryotes are symbiotic (2 organisms living in direct contact with each other). There are three types of symbioses: 1. Mutualism both symbiotic organisms benefit - e.g. Nitrogen-fixing bacteria like Rhizobium: plant obtain organic nitrogen, Rhizobium gets energy in the form of sugars that the plant produces. Another example: Slide 65 Are all prokaryotes disease producing germs? Without prokaryotes ecosystems would collapse! 53.10 Slide 66 54.1 An overview of ecosystem dynamics Slide 67 Methanogens in Peat Slide 68 54.18 The nitrogen cycle Slide 69 Slide 70 2. Commensalism one organism benefits and the other is not harmed. - e.g. Bacteria on our skin 3. Parasitism parasite benefits and the host is harmed. C. Pathogens cause human diseases - Some pathogens are opportunistic. They may be normal residents of the host, but if the host is weakened, then they cause disease. Slide 71 Slide 72 Lyme disease: Caused by a spirochete Slide 73 Slide 74 Red-band disease (RBD) consists of a narrow band of filamentous cyanobacteria that advances slowly across the surface of a coral, killing living tissue as it progresses. Slide 75 - How do we know if a particular organism is responsible for a disease? Robert Koch formed postulates as guidelines to establish that a disease is caused by a particular pathogen: a. Find same pathogen in each diseased individual. b. Isolate the pathogen and grow it in pure culture. c. Inoculate an individual with the isolated pathogen and the disease is induced. d. Isolate the same pathogen from the infected individual. This procedure is called Kochs Postulates and is used widely to determine what infectious agent causes disease. Slide 76 Most pathogens cause disease by producing poisons, these are either: - Exotoxins: proteins secreted by the pathogen that cause illness. - Endotoxins: poisons that are part of the pathogen that causes illness. (e.g. bacteriums outer membrane) Slide 77 D. Humans use prokaryotes in research and technology Examples: Sewage treatment Bioremediation Chemical & Medical production Research (genetic engineering, etc.) Slide 78 Slide 79 Figure 27.19 (p. 542) Bioremediation for an oil spill. Slide 80