sulfur cycle

what are the main pathways of the sulfur cycle

S assimilation, SO4 reduction, S oxidation, oxidation of Organic S

what are the largest reservoirs of sulfur

sedimentary rocks, specifically shales followed by evaporites

Dissimilatory SO₄^2- reduction

sulfate reduction:

• reduces SO₄^2- to HS- using either organic C or H2 as an e- donor

• SO₄^2- import -costs energy

• HS is highly toxic and excreted frm the cell

occurs in reduced sediments (no oxygen)

• example: hydrothermal springs

sulfur cycle simplified

oceans, volcanoes, and industries put dimethyl sulfide in atmosphere, becomes sulfur dioxide, turns into sulfuric acid and rains down to earth. assimilates into things, decomposes, and goes through the water cycle to go into oceans

sulfate assimilation in bacteria steps

1. sulfate

2. sulfite

3. sulfide

4. cysteine + acetate

5. cystathionine + succinate

6. homocysteine + NH3 + pyruvate

7. methionine + tetrahydrofolate

sulfide oxidation

chemolithoautotrophs can oxidize HS- and other intermediates using O2 or NO3- as electron receptor
anoxygenic photosynthesis development before oxygenic photosynthesis

what is beggiatoa

Genus of colorless, filamentous proteobacteria, up to 200 microns, among largest prokaryotes

hydrogen sulfide oxidation

stores elemental sulfur on its outer membrane after using sulfur during respiration

atmospheric sulfur inputs

natural emissions on land, human mining, sea salts, sea biogenic, sea volcanoes

total input: 272

humans activity: 90/272 so about 33%

largest is sea salts

atmospheric sulfur outputs

deposition on land, ocean deposition.

ocean deposition is twice of land

properties, sources, and effects of sulfur dioxide

properties: colorless gas with irritating odor

sources: 1/3 occur naturally, 2/3 from human sources, mostly combustion

effects: acid rain, breathing difficulties, eutrophication