Biomineralisation Flashcards
does dissolution involve breaking or making bonds
breaking
does precipitation involve making or breaking bonds
making bonds
what do you need to overcome to make a bond
activation energy barrier
what needs to happen for biomineralisation
- overcome electrostatic repulsions
- eliminate hydrogen shells around solutes
- remove ligands from solutes
- form new interface: nucleation
process of mineral nucleation and growthq
- Nucleation: formation of the nucleus of a new phase (the mineral) within the old phase (solution)
- Growth of initial phase: ions adsorb, starting at the nucleus (initial phase is usually amorphous)
- Growth of crystalline phase/dehydration and internal rearrangement
what does amorphous mean
not crystalline
what is saturation state defined by
the saturation index
Q=Ksp: SI=0:
Equilibrium
Q<Ksp: SI<0:
Undersaturated, can dissolve
Q>Ksp: SI>0:
Supersaturated, won’t dissolve, can precipitate
What is Q
ion activity product (IAP): same form as Ksp but for actual concentrations of ions in solution whereas Ksp is at equilibrium
what does Ksp mean
solubility product
what is biologically induced mineralisation
minerals form as a by-product of metabolic activity or other interactions between cells and their environment
what is biologically controlled mineralisation
the microorganism controls all stages of
mineralization to serve a physiological
purpose
2 mechanisms of biologically induced biomineralisiation
- cell surface reactivity - ionised surface functional groups (ligands) have low interfacial energies for nucleation
- metabolism - affecting saturation states and pH
examples of induced biomineralised products
ferrihydrite
mechanism and facilitated mechanisms for ferrihydrite
Totally passive mechanism (even dead cells can do this):
*Step 1: Fe adsorbed to EPS or cell wall
*Step 2: Nucleation - bacteria serve as nucleation sites
Cells become encrusted with ferrihydrite over time
Facilitated mechanisms (but not totally controlled by microbes):
1.Chemoheterotrophic iron mineralization
2.Anoxygenic photoautotrophic iron mineralization (photoferrotrophy)
3.Chemolithoautotrophic iron mineralization
Chemoheterotrophic iron mineralization
– “iron-depositing bacteria” – not true (metabolic) Fe-oxidisers because they don’t obtain energy from the process
– Have surface ligands that promote Fe(II)-oxidation
– Leptothrix ochracea – most common
– Sphaerotilus (image), Crenothrix, Clonothrix,
Metallogenium, Siderocapsaceae
- Anoxygenic photoautotrophic iron mineralization
(Photoferrotrophic growth):
-some GSB, PSB, PNB
– How does this happen without O2?
– E0 for Fe3+/Fe2+ too + to be PED except with very good TEA
– E0 for Fe(OH)3+HCO3/FeCO3 much less +, can be PED with various other TEAs.
3.Chemolithoautotrophic iron mineralization
- Using Fe(II) as an energy source (PED), TEA: O2 usually
- Most occurs at low pH, but this usually doesn’t form minerals
- At neutral pH, low O2, Gallionella ferruginea forms lots of ferrihydrite
- Form ferrihydrite stalks (top image)
- Ferrihydrite from G. ferruginea clogs wells, water pipes, drains etc.
Hydrothermal ferrihydrite precipitation
- Found along low O2 zones, from 2-50°C.
- Extensive deposits – some Gallionella (chemolithoautotrophs), others may be Leptothrix or other chemoheterotrophs
Magnetite
mixed Fe(II)-Fe(III) oxide: Fe3O4
- can be biologically induced or controlled
Induced biomineralization products are:
- poorly crystalline, small magnetite grains, mostly non-magnetic
Biogenic Mn-oxides are very common
- Form at the same oxic-anoxic interfaces as many ferrihydrites form
- At ca. pH 7, most Mn(IV)-oxide minerals attributed to microorganisms.
