The Sulfur Cycle Aerobic conditions Elemental sulfur Acid deposition H2S03 Beggiatoa, Thiobacillus 0 s02 Beggiatoa, Microbial Thiobacillus oxidation Burning of fossil fuels so Reduction by Desulfovibrio Assimilation by plants and bacteria SH sulfhydryl H2S groups of Decomposition proteins by microbes Purple and green (dissimilatory) phototrophic bacteria Purple and green phototrophic bacteria Anaerobic conditions (mostly soil and sediments) Elemental sulfur Figure 27.7 The Sulfur Cycle Figure 27.7