Sulfur cycle

Question 1

What is the oxidation state and name of S2-?

Answer 1

Sulfide, mercaptans

ox.state: -2

Question 2

What is the oxidation state and name of S0

Answer 2

Elemental sulfur

0

Question 3

What is the name and oxidation state of S2O4?

Answer 3

Hyposulfur

+2

Question 4

What is the name and oxidation state of SO3 2-

Answer 4

Sulfite

+4

Question 5

What is the name and oxidation state of SO4 2-

Answer 5

Sulfate

+6

Question 6

What is desulfuration?

Answer 6

R-SH => H2S

Decomposition of organic matter: yields H2S

Recycling of organosulfur compounds

Question 7

What is Sulfur respiration? In what condition does it happen?

Answer 7

Anaerobic condition

Reduction of S0 as terminal electron acceptor via anaerobic respiration (many species) : yields H2S

Question 8

What is sulfide and sulfur oxidation? What conditions?

Answer 8

Aerobic conditions

Ocidation of H2S and S0 , with O2 as TEA in energy generation

Question 9

What are examples of organisms that do sulfide and/or sulfur oxidation?

Answer 9

Bacteria

BEGGIATOA and THIOTHRIX (sulfur bacteria) => can oxidize H2S and accumulate S0 intracellularly
- Some species oxidize S0 to SO4 2-

Archea

SULFOLOBUS oxidizes S0, yiedling sulfuric acid

Chemolitotrophs => ACIDITHIOBACILLUS THIOOXIDANS
- (recall microbial oxidation of sulfidic ores results in sulfuric acid etc, production causing acid mine drainage)

Question 10

What is Chemotrophic oxidation of sulfide and sulfur? in what conditions?

Answer 10

Anaerobic conditions

H2S=> S0 => SO4 2-

• Oxidation of sulfides or sulfur with electron acceptors other than oxygen (anaerobic respiration) : yields S0 or SO4 2-

Question 11

Give example of organism doing chemotrophic oxidation of sulfide and sulfur

Answer 11

THIOMARGARITA and BEGGIATOA can use H2S as energy source with NO3- as TEA

Question 12

What is phototrophic oxidation of sulfide and sulfur? What conditions?

Answer 12

Anaerobic

Use sulfides or S0 as e- donor => yields S0 or SO4 2-

Similar to oxidation of H2O => H2 + O2 in oxygenic P/S

Question 13

What are examples of organisms doing phototrophic oxidation of sulfide and sulfur?

Answer 13

Chromatium (purple sulfur)

Chlorobium (green sulfur)

Question 14

Describe sulfate assimilation

Answer 14

Assimilatory sulfate reduction (done by many species)

• Similar to assimilatory nitrate reduction
• As cells only need a relatively very small amount of S this pathway is tightly regulated

Formation of a.a. (cys and met)

  - Assimilatory pathway is subject to end-product inhibition 
  - Dissimilatory sulfate reduction (like dissimilatory nitrate reduction) is not subject to end-product inhibition

Question 15

What is dissimilatory sulfate reduction?

Answer 15

-Sulfate reducing bacteria (SRBs)
=> Desulfovibrio

• Use SO4 20 as terminal electron acceptor in anaerobic respiration
• Use H2 and/or organic carbon as energy and electron source
  - H2S prouced is an important energy and electron source for other microorganisms

Question 16

Explain what is biological deposition of elemental sulfur? What are the 2 types of deposition?

Answer 16

S0 deposits form in lakes and geological formations
- Desulfovibrio, Thiobacillus, Chlorobium

• Initiated by dissimilatory sulfate reduction to H2S by SRBs such as Desulfovibrio

Oxidation of H2S to So in aquatic and geological environments (aerobically or anaerobically) contributes to S0 deposits

2 types:

Sulfur deposition via AEROBIC CHEMOTROPHIC sulfide oxidation
-H2S can be oxidized to S0 by Thiobacillus

Sulfur deposition via ANAEROBIC PHOTOTROPHIC sulfide oxidation
- H2S can be oxidized to S0 by phototrophs such as Chlorobium, providing there is is light