Biologically Induced Biomineralisation

Question 1

What is biologically induced biomineralisation?

Answer 1

Minerals form as a by-product of metabolic activity or cell interactions with the environment.

External/extracellular
Passive

Question 2

What are the two main mechanisms?

Answer 2

1. Cell surface reactivity
   - Ionised functional groups on cell surfaces have low energies for nucleation.
   - Nucleate easily at low activation energies
   - Speed up mineral ppt.
2. Metabolism
   - Production of biominerals as by-product of metabolism
   - Environmental conditions can favour ppt.

Question 3

What is the main Iron mineral that is biologically induced?

Answer 3

Fe(OH)3 - Ferrihydrite

• Geologically widespread biomineral
• Forms in association with microbial biomass
• When Fe(II) comes into contact with O2

Question 4

What is the passive mechanism for ferrihydrite biomineralisation?

Answer 4

• Fe adsorbed in EPS or cell wall
• Nucleation (bacteria serve as nucleation sites)
• Cells become encrusted with ferrihydrite

Question 5

What are the 3 groups that facilitate iron biomineralisation? not passive

Answer 5

1. Chemoheterotrophic iron mineralisation
   - Surface ligands promote Fe(II)-oxidation
2. Anoxygenic photoautotrophic iron mineralisation
   - Iron oxidised without O2
   - E.g., GSB, PSB, PNB
3. Chemolithoautotrophic iron mineralisation
   - low O2, neutral pH, form lots of ferrihydrite

Question 6

Where is hydrothermal ferrihydrite precipitation found?

Answer 6

Low O2 zones - get extensive ocean deposits

E.g., Gallionella (Chemolithoautotrophic iron oxidiser) or chemoheterotrophs

Question 7

What other iron mineral is biologically induced?

Answer 7

Magnetite - Fe3O4 - mix of Fe(II) and Fe(III)

Question 8

How is magnetite biomineralised?

Answer 8

Typically formed in sub-oxic transition zones.

Mineralised by Dissimilatroy Fe(III) reducers (anerobic chemoheterotrophs) e.g., Shewanella

Question 9

Where do manganese minerals biomineralise?

Answer 9

Form at oxic-anoxic interfaces.

Mn(II) can migrate and accumulate in pore waters.

Question 10

When do sulphide minerals biomineralise?

Answer 10

SRB (anaerobic chemoheterotroph) reduce sulphate to sulphide (HS- or H2S).

Sulphide reacts with metals in the environment to produce metal sulphides

Question 11

What is the role of photosynthetic cyanobacteria in carbonate biomineralisation?

Answer 11

1. Fix carbon
   - Done by autotrophs
   - Increases pH, leads to supersaturation and ppt.
2. Cell surfaces catalyse nucleation
   - Presence of EPS and Sheaths allows for more calcite ppt.