Lecture 24: Microbial Processes

Question 1

How are microbial mats formed?

Answer 1

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

Question 2

What is a stromatolite?

Answer 2

The lithified version of a microbial mat

Question 3

What is depeotonization?

Answer 3

The release of a proton into a solution

Question 4

What is the most important compound for surface charge?

Answer 4

The carboxyl group

Question 5

What are the four biomediatio strategies?

Answer 5

1) Biosorption
2) Bioaccumulation
3) Biotransformation
4) Biomineralization

Question 6

What is biosorption?

Answer 6

The process whereby microbial biomass acts as a surface upon which toxic metals and radionuclides are passively absorbed

Question 7

What is bioaccumulation?

Answer 7

Describes the metabolic processes used by living biomass in which physiologically-important metal ion are absorbed by cells

Question 8

What is biotransformation?

Answer 8

The reduction of high valence metals to lower valence insoluble species, or oxidation that leads to the opposite effect

Question 9

What is biomineralization?

Answer 9

The formation of insoluble mineral phases

Question 10

What are the two ways microorganisms form mineral phases?

Answer 10

1) Biologically induced biomineralization

2) biologically controlled biomineralization

Question 11

What is biologically induced biomineralization?

Answer 11

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

Question 12

What is biologically controlled biomineralization?

Answer 12

Biomineralization that is completely regulated, allowing the organism to precipitate minerals that serve physiological roles

Question 13

What are the two steps of induced biomineralization?

Answer 13

1) Metal binds to cell surface

2) Metals react with anions from solution

Question 14

What biomineral is produced in hot springs?

Answer 14

Amorphous silica

Question 15

What are the two steps of carbonate precipitation with photosynthetic bacteria?

Answer 15

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

Question 16

What are the steps of controlled biomineralization?

Answer 16

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.

Question 17

What minerals make up the largest fraction of known controlled biomineralization?

Answer 17

Calcium carbonate

Question 18

How does bioweathering occur?

Answer 18

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

Question 19

What are endolithic bacteria?

Answer 19

Organisms that live inside rocks or in pores between mineral grains
-Leads to the solubilization of cementing mineral grains

Question 20

What are the two ways that organic acids increase mineral dissolution?

Answer 20

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.

Question 21

What are chelators?

Answer 21

Organic anions involved in chelation

Question 22

What is bioleaching?

Answer 22

Refers to the use of bacteria to leach metals from a sulfide mineral