Lecture 24: Microbial Processes Flashcards
-Biofilms and Microbial Mats -Biosorption -Biomineralization -Bioweathering
How are microbial mats formed?
Surfaces in an aquatic system is rapidly colonized by bacteria.
- The bacteria then produce an organic material called extracellular polysaccharides (EPS), which allows more bacteria to stick to the surface.
- This forms a biofilm, but given time and a sufficient supply of energy, a biofilm thickens into a microbial mat
What is a stromatolite?
The lithified version of a microbial mat
What is depeotonization?
The release of a proton into a solution
What is the most important compound for surface charge?
The carboxyl group
What are the four biomediatio strategies?
1) Biosorption
2) Bioaccumulation
3) Biotransformation
4) Biomineralization
What is biosorption?
The process whereby microbial biomass acts as a surface upon which toxic metals and radionuclides are passively absorbed
What is bioaccumulation?
Describes the metabolic processes used by living biomass in which physiologically-important metal ion are absorbed by cells
What is biotransformation?
The reduction of high valence metals to lower valence insoluble species, or oxidation that leads to the opposite effect
What is biomineralization?
The formation of insoluble mineral phases
What are the two ways microorganisms form mineral phases?
1) Biologically induced biomineralization
2) biologically controlled biomineralization
What is biologically induced biomineralization?
Biomineralization that occurs without any apparent regulation or control.
-Biominerals form as incidental by-product due to the activity of the microorganism and their surrounding environment
What is biologically controlled biomineralization?
Biomineralization that is completely regulated, allowing the organism to precipitate minerals that serve physiological roles
What are the two steps of induced biomineralization?
1) Metal binds to cell surface
2) Metals react with anions from solution
What biomineral is produced in hot springs?
Amorphous silica
What are the two steps of carbonate precipitation with photosynthetic bacteria?
1) Metabolic fixation of inorganic carbon tends to increase solution pH and leads to an increase in the saturation state
2) Cation absorption to the sheath promotes biomineralization
What are the steps of controlled biomineralization?
1) A specific site within the cell is sealed off from the external environment.
2) The cell sequesters specific ions and transfer them to the isolated compartments where their concentrations are increased until a state of supersaturation is reached.
3) The crystals grow in an ordered manner, having their orientation and size governed by the shape and size of the membrane-bound compartment.
What minerals make up the largest fraction of known controlled biomineralization?
Calcium carbonate
How does bioweathering occur?
Hyphae (fungal filaments) exploit grain boundaries, cleavage and cracks to gain access to new mineral surfaces
-By doing this, they cause extensive physical disintegration of the minerals
What are endolithic bacteria?
Organisms that live inside rocks or in pores between mineral grains
-Leads to the solubilization of cementing mineral grains
What are the two ways that organic acids increase mineral dissolution?
1) They release protons to attack minerals directly
2) (Chelation) Deprotonated organic anions indirectly affect dissolution rates by complexing with metal cations in the solution, thereby lowering the minerals saturation state.
What are chelators?
Organic anions involved in chelation
What is bioleaching?
Refers to the use of bacteria to leach metals from a sulfide mineral
