1. Sulfur
• 0.06% of earth’s crust
• Sources
• Original sources sulfides in metals contained in
plutonic rocks
• Organic matter (S-containing amino acids)
• Ca, Mg, Na, K, NH4 sulfates (in arid areas)
• Atmosphere, as sulfur dioxide (SO2) especially
as pollutants of industrial
• processes e.g., ore smelting, petroleum refining.
• Sulfides in small amounts (in waterlogged soils)
– H2S
• Pyrites – FeS2
• Gypsum
• Organic sulfur
• The critical C:S ratio in
carbonaceous materials
above which
immobilization is
dominant to
mineralization is
reported to be
approximately 50:1
• Drying of soil enhances
mineralization of S
• SO4 = is easily lost by
leaching due to its
organic nature.
2. Sulfur
• Organisms involved in S
mineralization
• Microsporeum - (fungi)
• Scopulariopsis - (fungi)
• Aspergillus - (fungi)
• Mineralization of Sulfur
• Sulfur mineralization occurs under
conditions that are proper and
favorable for microbial activity.
• The sulfur compounds that are
mineralized are those in plant,
animal, and microbial proteins
(specifically the amino acids –
cysteine and methionine, B
vitamin, thiamine, biotin, folic
acid).
3. Sulfur
• Sulfur Oxidation
• In soil, sulfides, elemental sulfur,
and thiosulfate can be oxidized
slowly by chemical means, but the
microbiological oxidation is far
more rapid when conditions are
favorable.
• The sulfur oxidizers are several
kinds of bacteria such as,
Thiobacillus spp, Beggiatoa,
Thiorix, Thioplaca, and others.
• Sulfur Reduction
• In soils they become deficient in
oxygen as by flooding, sulfate
concentration falls and sulfide
level increases. This is due to the
increase activity of sulfate
reducing bacteria.
• The predominant microorganisms
concerned with the reduction of
sulfate are bacteria of the genus
Desulfovibrio.
