The Sulfur Cycle
These are often termed as follows:
Assimilative sulfate reduction (sulfur assimilation) in which sulfate (SO42–) is reduced to organic sulfhydryl groups (R–SH) by plants, fungi and prokaryotes. The oxidation states of sulfur are +6 in sulfate and –2 in R–SH.
Desulfuration and Dissimilative sulfur reduction in which organic molecules containing sulfur can be desulfurated, producing H2S. 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 produces sulfate.