Soil Microbiology Flashcards
Ecosystem
The sum of all organisms & abiotic factors in a particular environment
Habitat
Portion of an ecosystem where a community could reside
Population
Group of microorganisms of same species residing in same place at same time
Community
A group of populations
Species richness
The total number of different species present
Species abundance
The proportion of each species in an ecosystem
Guild
Metabolically related microbial populations
Niche
Habitat shared by a guild
Prime niche
Niche in which the organism is most successful
Microenvironment
The immediate environmental surroundings of a microbial cell or group of cells
* Physiochemical conditions are subject to rapid change
* Resources in natural environments are highly variable
Parasitism
one member in the relationship is harmed and the other benefits
Mutualism
both species benefit
Commensalism
one species benefits and the other is neither harmed nor helped
Biogeochemical cycle
Transformation of key elements by biological and chemical agents
Soil
Loose outer material of Earth’s surface
Types of Soil
- Mineral soil
- Organic soil
Mineral soil
Derived from rock weathering and other inorganic materials
Organic soil
Derived from sedimentation in bogs and marshes
Soil composition
- Inorganic material (40%)
- Organic material (5%)
- Air and water (50%)
- Living organisms (5%)
Soil structure
- O Horizon:
- A Horizon:
- B Horizon:
- C Horizon:
O Horizon
Layer of undecomposed plant materials – top layer
A Horizon
Surface soil rich in organic material, full of life
B Horizon
Subsoil made of decomposed organic material and humus
C Horizon
Soil base which develops directly from underlying bedrock
Water availability of different soils
- Sand: Water drains quickly
- Silt: Retains water to the right extent
- Clay:Water retained too well, and soil becomes anoxic
Most important factors influencing microbial activity in soil
- The availability of water in surface soils
- Nutrient availability in subsurface soils
Functions of bacteria/Archaea in soil
- Production of the humus
- Release of minerals from soil particles
- Cycling of nutrients (C, N, S)
- Nitrogen fixation
Rhizospere
Soil that surrounds plant roots and receive plant secretions
Nitrogen fixation
Start/End product? Enzyme? Conditions? Electrons required?
- Conversion of atlospheric nitrogen (N2) into ammonia (NH3)
- Reaction is catalyzed by nitrogenase complex
- Dinitrogenase reductase is inhibited by the presence of oxygen
- Requires 8 electrons
Free-living nitrogen fixers
Clostridium, Azotobacter, Cyanobacteria
Clostridium
strict anaerobe
Azotobacter
Strict aerobe
* Very high rate of O2 consumption keeps the intracellular environment anaerobic
Cyanobacteria
Nitrogen fixation occurs in specialized anaerobic cells (heterocysts) which lack Photosystem II
Adaptations of heterocyts
- Thick cell wall that slow down the diffusion of O2
- The regular cells provide the heterocysts with carbohydrate
Symbiotic nitrgen fixers
- Colonization of legume roots
- Formation of root nodules that fix nitrogen
Nodule formation
- Recognition & attachment of bacterium to root hairs
- Excretion of nod factors by the bacterium
- Bacterial invasion of the root hair
- Travel to the main root via the infection thread
- Formation of bacteroid state within plant cell
- Continued plant and bacterial division, forming the mature root nodule
O2 regulation in root nodules
Oxygen levels are controlled by leghemoglobin, produced by plant cells
