Week 2: Geomicrobiology 4 - mineral transformations - DEGREDATION

Question 1

What can mineral transformations involve?

Answer 1

mineral attack and mineral formation

Question 2

What is mineral attack?

Answer 2

dissolution, degradation, (bio)deterioration, bioweathering

Question 3

What is mineral formation?

Answer 3

biomineralization

Question 4

What are ways a microbe can attack a mineral?

Answer 4

enzymatically or non-enzymatically

Question 5

What determines if a microbe can attack a mineral with direct enzymatic attack? (enzymatically)

Answer 5

Key enzymes that react with geosubstrate are in the outer membrane, e.g. of Gram-negative bacteria

Question 6

What determines if a microbe can attack a mineral with indirect enzymatic attack? (non-enzymatic)

Answer 6

Key enzymes for formation of georeactive metabolic products are below cell envelope in cytoplasm of prokaryotes (bacteria) and in cytoplasm/cell organelles of eukaryotes (fungi, algae, lichens)

Question 7

What can direct enzymatic attack be?

Answer 7

Direct enzymatic attack of a mineral is either oxidative or reductive

Question 8

What does direct enzymatic attack of a mineral (oxidative or reductive) need?

Answer 8

• Presence of an oxidizable or reducible mineral constituent will require…
• Attachment of the cells to the mineral surface
• Enzymes capable of reduction/oxidation located at cell surface
• Enzyme must be in contact with mineral surface…..

Question 9

What are examples of enzymatically-catalysed geochemical transformation? (aerobic)

Answer 9

oxidation occurs
- bacterial Mn(II) oxidation to Mn(IV) oxide
- bacterial Fe(II) oxidation to Fe(III) oxide or oxyhydroxide
- bacterial So oxidation to SO42-
- mineral sulphides (e.g. pyrite (FeS2), arsenopyrite (FeAsS), sphalerite (ZnS), chalcopyrite (CuFeS2)) to corresponding metal sulphates
- uraninite (UO2) to UO22+
- Cr(VI)O42- reduction to Cr(III)

Question 10

What is an example of enzymatically-catalysed geochemical transformation? (anaerobic)

Answer 10

reduction occurs

• bacterial reduction of Mn(IV)O2 to Mn2+
• bacterial reduction of Fe2O3 to Fe2+
• bacterial reduction of SO42- to HS-
• bacterial reduction of SeO32- to Seo
• methanogenesis – anaerobic reduction of CO2 to CH4

Question 11

What happens in enzymatically-catalysed geochemical transformation for aerobic and anaerobic conditions?

Answer 11

anaerobic = reduction
aerobic = oxidation

Question 12

What is required for indirect non-enzymatic attack of minerals?

Answer 12

reactive products of microbial metabolism

Question 13

What are the reactive products of microbial metabolism that are required for indirect non-enzymatic attack of minerals?

Answer 13

• Needs the presence of a susceptible mineral constituent
• Attachment of the cells to the mineral is not necessary – reactive products excreted into the bulk phase
• Depending on the metabolite and the mineral, mineral dissolution or formation may result by:
  -oxidation or reduction
  -acid or base attack
  -complexation

Question 14

Is attachment of the cells to the mineral necessary in non-enzymatic attack?

Answer 14

NO

Question 15

What can result in metabolite-mineral dissolution? (non-enzymatic attack)

Answer 15

Depending on the metabolite and the mineral, mineral dissolution or formation may result by:
-oxidation or reduction
-acid or base attack
-complexation

Question 16

What are examples of non-enzymatic indirect geochemical transformations? (mineral dissolution or weathering)

Answer 16

Carbonates, e.g. limestone

Phosphates and silicates, e.g. apatite, aluminosilicates

Question 17

How can indirect non-enzymatic attack geochemically transform carbonates?

Answer 17

Carbonates, e.g. limestone

1. Affected by corrosive metabolic products, e.g. H2CO3, HCOOH, H2SO4 and HNO3
2. organic acids, e.g. acetic, oxalic, citric, lactic, pyruvic, etc –

These can cause acid dissolution or withdrawal of Ca2+ by complexation

• H2CO3 formed from respiratory CO2
• HNO3 from oxidation of NH4+ by nitrifying bacteria
• H2SO4 from sulfide-oxidizing bacteria

Question 18

How can indirect non-enzymatic attack geochemically transform phosphates and silicates?

Answer 18

e.g. apatite, aluminosilicates

As above except that H2CO3 too weak for these minerals: role for organic acids

Question 19

How can cobalt phosphate be made available to other organisms and plants?

Answer 19

dissolution by citric and oxalic acids produced by soil fungi

Question 20

What are organic acids important for?

Answer 20

mineral dissolution and formation

precipitation of insoluble mycogenic oxalates

Question 21

Can sulfides be involved in mechanisms of biogenic mineral degradation?

Answer 21

yes

Question 22

What 2 types of biogenic mineral degradation are sulfides involved in?

Answer 22

enzymatic and non-enzymatic

Question 23

What is the sulfide enzymatic degradation process? (enzymatic)

Answer 23

Aerobic processes: Metal sulfides
Chalcocite oxidation:
Enzymatic (Direct)
Cu2S + 0.5O2 + 2H+ –> Cu2+ + CuS + H2O
CuS + 2O2 –> Cu2+ + SO42-

Question 24

What is the sulfide enzymatic degradation process? (non-enzymatic)

Answer 24

Non-enzymatic (Indirect): Fe2+ in bulk phase is oxidized, Fe(III) then acts as chemical oxidant:
2Fe2+ + 0.5O2 + 2H+ –> 2Fe3+ + H2O
Cu2S + 2Fe3+ –> Cu2+ + CuS + 2Fe2+
CuS + 2Fe3+ –> Cu2+ + S0 + 2Fe2+

e.g. Acidithiobacillus ferrooxidans (D, I)

Question 25

Can manganese (Mn) be involved in mechanisms of biogenic mineral degradation?

Answer 25

YES

Question 26

What is the ENZYMATIC enzymatic degradation process? (non-enzymatic)

Answer 26

Anaerobic Processes: Mn(IV) oxide to soluble Mn2+
Enzymatic (Direct)

4MnO2 + CH3COO- + 7H+ –> 2HCO3- + 4Mn2+ + 4H2O

e.g. Geobacter metallireducens, Shewanella oneidensis

Question 27

What is the NON-ENZYMATIC enzymatic degradation process? (non-enzymatic)

Answer 27

Non-enzymatic (Indirect) (aerobic)
MnO2 + HOOCCOO- + 3H+ –> Mn2+ + 2CO2 + 2H2O
e
.g. various oxalate-producing fungi