Controlled Biomineralisation

Question 1

What is controlled biomineralisation?

Answer 1

Microorganism control mineralisation.

• Intracellular (in cytoplasma) or Epicellular (in cell wall)
• Specific ions are actively introduced and controlled until SI is reached for ppt.
• Requires energy
• Minerals form regardless of external environment

Question 2

What is the mechanism process for controlled biomineralisation?

Answer 2

1. Site has to be sealed from environment (e.g., intracellular deposition vesicle)
2. Ions are transported to mineralisation site for supersaturation
3. Nucleation of mineral, controlled by organic ligands
4. Crystal growth (highly ordered)

Question 3

What are magnetosomes found in magnetite bacteria?

Answer 3

Intracellular, linearly arranged membrane bound structure where Fe3O4 (Magnetite) is precipitated.

Question 4

What are the characteristics of magnetotactic microbial bacteria?

Answer 4

• Chemically pure
• Chains, align cells like compass needle
• Require O2, oxidised and reduced iron
• Chemoheterotrophic, O2 as TEA

Question 5

Why are magneto-tactic bacteria important?

Answer 5

Are Magnetofossils:
- useful for studying palaeomagnetism and palaeoenironmental changes

Magnetotaxis:

• May help microaerophillic bacteria navigate along magnetic field lines to find optimum O2 level.
• Not entirely known as horizontal magnetic fields are at the equator but still get this bacteria here.

Question 6

What is Greigite?

Answer 6

Fe3S4 - Iron sulphide

• Similar to intracellular magnetite, has chains, magneto-tactic bacteria
• But formed in anoxic environments
• 1/3rd as magnetic as magnetite, but more magnetosomes

Question 7

What forms amorphous silica and what do they contribute to?

Answer 7

Formed by eukaryotes e.g., Diatoms

Contribute to seafloor silica and ocean primary productivity.

Question 8

Why are silica shells formed in silica undersaturated environments?

Answer 8

Potentially due to genetic holdover from the silica rich world.
Not entirely known.

Question 9

How are silica shells formed?

Answer 9

• Extract Si(OH)4 from water
• Pump to intracellular deposition vesicles
• Silica added to vesicles until supersaturated
• NH3 and OH- functional groups react with silica, catalyse nucleation

Question 10

What are the two types of calcite minerals?

Answer 10

1. Coccolithophores
   - Exploded early cretaceous
2. Formanifera
   - Eat bacteria, protozoa etc.
   - > 90% of deep sea biomass