Sulfur Cycle: Sulfur is an essential part of cells. Green and purple sulfur bacteria oxidize hydrogen sulfide for photosynthesis. The source of hydrogen sulfide is usually decaying organic matter or minerals in the soil. As the bacteria decompose organic or inorganic forms of sulfur, hydrogen sulfide is released to the air. It is oxidized to produce sulfur dioxide which falls to the earth in rain. Here it is taken up by plants to make amino acids, where it travels through the food web and back to decomposition. Sulfur Cycle retrieved on 5/12/07 from. Some bacteria in wetlands make the organic molecules that can be nutrients for other life forms. ' Photosynthetic bacteria such as the purple sulfur bacteria found in salt marshes and mud flats can produce organic matter using sulfur and light: