Chapter 22 Flashcards
Relationships between microbes
Symbiosis—rela:onships between microbes
• Parasite—microorganism benefits at the expense of the host
• Pathogenic—microorganism causes disease in the host
• Commensal—microorganism does not affect host
• Mutualis:c—the microbe benefits the host
Symbioses between microbes: Liche
Fungus and alga or cyanobacteria living in symbiosis with one another
• Phototroph produces organic material for fungus
• Fungus
Fungus and alga or cyanobacteria living in symbiosis with one another
• Phototroph produces organic material for fungus
• Fungus
Anchors phototroph– Produces lichen acids to
dissolve inorganic nutrients – Water uptake
Consortia
Microbial mutualisms
• Example: 13-‐‐69 Non-‐‐mo:le phototrophic green sulfur bacteria (epibionts) and one mo:le non-‐‐phototrophic bacteria
Consortia
Epibiont in genus Chlorobium
• Scotophobotaxis• Chemotaxis towards sulfide • Fusion of periplasms• Epibiont supplies α-‐‐ketoglutarate to central
microbe
Legume-‐‐root nodule symbiosi
- Legumes—clover, alfalfa, beans, peas, soybeans
- Rhizobia—nitrogen-‐‐fixing symbionts of plants
- Root nodules—rhizobial infec:on of legume roots
Root nodules
Leghemoglobin—binds oxygen to protect nitrogenases, produced by rhizobia
• 10,000:1—bound oxygen:free oxygen in nodules
Bacteroid
differen:ated rhizobial cell
Stem nodules on Sesbania are formed
by Azorhizobium
Tropical aqua:c legumes
• Some contain Bradyrhizobium -‐‐ photosynthe:c
Non-‐‐legume nitrogen-‐‐fixing symbiosis
Azolla-‐‐Anabaena
– Rice paddies
– Red arrow -‐‐ heterocyst
• Alnus-‐‐Frankia
– Vesicles for N2 fixa:on
Agrobacterium and crown gall disease
Uncontrolled growth of :ssue
• A. tumefaciens
• Ti (tumor inducing) plasmid must be presen
Agrobacterium T-‐‐DNA is transferred to the plant
Genes for tumor forma:on and opines
• Opines—modified amino acids that serve as source of carbon and nitrogen for bacteria
– Octopine– Nopaline
Symbioses between microbes: Mycorrhizae
• “fungus root” • Partners coevolved • Photosynthe:c partner
provides carbon compounds
• Fungal partner allows for
absorp:on and nutrient availability
Symbioses between microbes: Endomycorrhizae
• Fungal mycelium embeds in root :ssue • Most common—arbuscular mycorrhizae -‐‐
Glomeromycota
• Hyphopodium (HP)—aeachment structure • Spore (SP)
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