Microbiology Module 12.2

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  1. Types of Symbiotic Relationships
    • Symbiosis is the living together or close association of 2 dissimilar organisms
    • 1. Mutualism: 2 organisms living together and both benefit from relationship
    • 2. Commensalism: Neither symbiont. Typically one benefits
    • 3. Paratism: Host cell is harmed, but parasite benefits
    • 4. Predation: Predator kills and consumes prey (not real type of symbiosis)
  2. Mutualism: Nitrogen Fixing by Rhizobia
    • 1. When nitrogen is too low, plant root release flavonoids (chemoattractants) to attract bacteria
    • 2. Bacteria chemotax to plant roots, make NOD factors which cause plant cells to divide and root hairs curl
    • 3. Bacteria invade plant cells and divide along with plant cells
    • 4. Differentiate into bacteriods (non-growing, N2 fixing)
  3. Nitrogen Fixation in Legumes
    • Infection thread: invagination of CM which forms pathway for bacteria to enter cell. Bacteria and cell proliferation will form nodules
    • Leghemoglobin (protein made by plants, heme by bacteria) keeps oxygen away from bacteria
    • Rhyzobia require nutrients provided by the host used to generate ATP & reducing power for nitrogen fixing
  4. Mutualism: Termite-Trichonympha
    • Most multi-celled animals do not produce cellulase and cannot digest plant food
    • Protozoan Trichonympha which digests wood in ingested by termites
    • Trichonympha gets protection & Termites get food source
  5. Lichens (Mutualistic)
    • Relationship between a fungus and a photosynthetic partner: Fungus-alga or fungus-cyanobacteria
    • Fungi protect partner from drying out and secrete acids to dissolve inorganics from rocks
    • Photoautotrophs provide food by CO2 fixation; also N2 fixation by some cyanobacteria
  6. Mutualism in ruminants
    • Ruminants digest cellulose by harboring cellulose in their rumens
    • Rumen highly anaerobic. Large intestine anaerobic as well
    • pH of rumen is neutral
    • Rumen contain ~200 species of bacteria, lower #'s of protozoa
    • Cellulose broken down in rumen and ferment sugars to vFA's <-- main carbon source for cows
    • Methanogens in rumes which convert H2 and CO2 to CH4
    • Abomasum: True stomach
  7. Predation in microbes
    All of these species invade microbe and consume microbe from inside out
  8. Normal human microbes
    • Humans harbor 10 to the 14 microbes
    • 10-20% of microbes potential pathogens
    • Large numbers of non-pathogens outcompete pathogens for nutrients and space
  9. Bacteria Colon
    • Large # of microbes (10 to the 13 eliminated each day), mostly anaerobes
    • Microbes growing on shed epithelial cells or on undigested foods. Pathogens try to grow on epithelial of intestines
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46948
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Microbiology Module 12.2
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Module 12.2
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