Sulfur Cycle Facts• Sulfur Oxidation States

– Sulfide and organic sulfhydryl groups = -2– Elemental sulfur = 0– Thiosulfate (S2O3

-2) = +2– Sulfite (SO3

-2) = +4– Sulfate (SO4

-2) = +6

• Sources of sulfur to the global cycle?– Weathering & volcanism & sea-spray– Biological emission of Dimethyl Sulfide (DMS) from oceans.– Fossil fuel combustion (photo-oxidation of SO2).

• Most sulfur is in seawater and sedimentary rocks.

• Assimilatory sulfate reduction:– Incorporates sulfate into methionine and cystein (amino acids).– Only some anaerobes assimilate S-2 directly to organic matter.

Global Input and Outputs

Sulfur Cycling

Sº Desulfuromonas

Hypereutrophic Lakes

• Very high primary production at the surface and thermocline.

• Organic particles sink to hypolimnion and sediments, which have become anaerobic by summer due to stratification.

• Anaerobic decomposition will release sulfide by desulfurylation and sulfate reducing bacteria; the later is more dominant with increasing sulfate of Sº supply.

• Diffusion of sulfide to illuminated water supports anoxygenic phototrophy and Sº .

• Diffusion of sulfide to microaerobic zone supports SOB and Sº.

Sº

Protocooperation

Lake Fryxell

• Appearances are similar.

• Although reverse stratification.

• Sulfide source from the bottom and oxygen at the “surface”.

• Why no sulfur phototrophs?

- purple sulfur (Chromatium) - green sulfur (Chlorobium)

• How does the S-cycle complete itself?

Sulfide OxidizersLike IOBs, these SOBs favor microaerobic

conditions and may be isolated by gradient tubes.

What about SOAs (A=archaea)?

Symbiotic Sulfide

Oxidizing Bacteria

Infers protection of animal tissues from toxic sulfides.

Animal feeds off of the organic matter produced by these chemolithoautotrophs.

There’s a happy marine nematode woven inside this filamentous SOB!

Endosymbiotic SOB of marine

invertebratesSolemya velum, the Atlantic Awningclam is a salt marsh clam without feeding gills.

Riftia pachyptila Giant Tube Worms …

Microbial Mats(No not me!)

Coral Disease (e.g. BBD)

Black Band Disease’s mobile microbial mat community

Phormidium corallyticum

Beggiatoa spp.LIVE CORAL

DEAD CORAL

Spread rate ~1 cm/d