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Sulfur cycle
Cyclic movement of sulfur in different chemical forms from the environment, to organisms, and then back to the environment. (source: EPA) Background from Wikipedia Sulfur is one of the constituents of many proteins, vitamins and hormones. It recycles as in other biogeochemical cycles. The essential steps of the sulfur cycle are: Mineralization of organic sulfur to the inorganic form, hydrogen sulfide: (H2S). Oxidation of sulfide and elemental sulfur (S) and related compounds to sulfate (SO42–). Reduction of sulfate to sulfide. Microbial immobilization of the sulfur compounds and subsequent incorporation into the organic form of sulfur.These are often termed as follows: Assimilative sulfate reduction (see also sulfur assimilation) in which sulfate (SO42–) is reduced to organic sulfhydryl groups (R–SH) by plants, fungi and various prokaryotes. The oxidation states of sulfur are +6 in sulfate and –2 in R–SH. Desulfuration in which organic molecules containing sulfur can be desulfurated, producing hydrogen sulfide gas (H2S), oxidation state = –2. Note the similarity to deamination. Oxidation of hydrogen sulfide produces elemental sulfur (So), oxidation state = 0. This reaction is done by the photosynthetic green and purple sulfur bacteria and some chemolithotrophs. Further oxidation of elemental sulfur by sulfur oxidizers produces sulfate. Dissimilative sulfur reduction in which elemental sulfur can be reduced to hydrogen sulfide. Dissimilative sulfate reduction in which sulfate reducers generate hydrogen sulfide from sulfate.Human impact on the sulfur cycle is primarily in the production of sulfur dioxide (SO2) from industry (e.g. burning coal) and the internal combustion engine. Sulfur dioxide can precipitate onto surfaces where it can be oxidized to sulfate in the soil (it is also toxic to some plants), reduced to sulfide in the atmosphere, or oxidized to sulfate in the atmosphere as sulfuric acid, a principal component of acid rain. AScribe (press release)The "record of sulfur isotopes captures the widespread and possibly permanent activation of the oxidative sulfur cycle, for perhaps the first time in Earth Full Text - Oct 11, 2007 Science Magazine (subscription)...the jovian magnetosphere, leading to a radiolytic sulfur cycle on thousand-year time scales between elemental sulfur, sulfur dioxide, and sulfuric acid, Full Text - Sep 27, 2007 Science Magazine (subscription)...greater surface ocean oxygenation above 153 m, including changes in 34 S- 33 S systematics that may record the onset of an oxidative sulfur cycle (23). Slowing Global Warming by Enhancing the Natural Sulfur Cycle - Jul 24, 2007 PR Web (press release),Scientists have proposed a limited iron fertilization of the Southern Ocean as a means to stimulate the natural sulfur cycle associated with marine Marine Phytoplankton and Clouds - Mar 13, 2007 CO2 Science Magazine,Biogenically driven organic contribution to marine aerosol. Nature 431: 676-680. Shaw, GE 1983. Bio-controlled thermostasis involving the sulfur cycle. Snottites, Other Biofilms Hasten Cave Formation - Dec 11, 2006 State College News,...may convert the sulfuric acid to hydrogen sulfide, creating a complete sulfur cycle in a few microns. microbes to survive. Cave biofilm layers also fulfill Study in "stinky places" finds cave-carving bacteria - Dec 12, 2006 Xinhua,These layers can convert the sulfuric acid to hydrogen sulfide, creating a complete sulfur cycle along a cave wall or floor. News index | RSS | News Feed Advertisements: Organic Apparel from Patagonia | Insect-repelling clothing |
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