In its elementary form, sulphur cannot be used by either plants or animals. Yet some bacteria can oxidize sulphur into sulphate which is easily used by all forms of life. Plants, for example, get the sulphur they need from sulphates in order to synthesize some amino acids (cystine, cysteine, methionine) that are in turn essential for protein synthesis.
Bacteria Thiobacillus thiooxidans
oxidize sulphur into sulphate (SO42-
). This is an aerobic chemo-autotrophic process during which acid is produced, resulting in a lowering of the pH of alkaline soils. Dead plants and soil microorganisms degrade sulphur-containing proteins into amino acids. These are degraded by an enzyme called desulfurase found in anaerobic bacteria of the genus Desulfotomaculum
. Sulphur is released as hydrogen sulphide (H2
S). Some species of green and purple phototrophic bacteria can oxidize hydrogen sulphide produced by sulphate reduction and amino acid decomposition. This oxidation process produces elemental sulphur (S).
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