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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)
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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)
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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
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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
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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
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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
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Predation in microbes
All of these species invade microbe and consume microbe from inside out
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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
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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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