The document discusses the iron cycle, highlighting its importance as one of the most abundant elements on Earth and its various forms in different oxidation states. It describes the processes of ferrous iron oxidation and ferric iron reduction, detailing the microorganisms involved in each process. Overall, it outlines the biogeochemical cycling of iron through various spheres of the Earth.

1. IRON CYCLE
B. LOKESHWARI
II M. Sc MICROBIOLOGY
SACRED HEART COLLEGE (AUTONOMOUS)
TIRUPATTUR.

2. INTRODUCTION
• Iron (Fe) is one of the most abundant elements in Earth’s crust.
• Biogeo chemical cycle of Iron through the Atmosphere, Hydrosphere,
Biosphere and Lithosphere.
• A third oxidation state, Fe0 is abundant in Earth’s core and is also a major
product of human activities from the smelting of Iron ores to form Cast iron.
• On the surface of earth, Iron exists naturally in Two oxidation states;

3. 1. Ferrous
iron
oxidation
2. Ferric iron
reduction

4. 1. FERROUS IRON OXIDATION
• Ferric iron (Fe3+) is reduced to the Iron ore (Fe0) and then oxidized to Ferrous iron
(Fe2+).
• The oxidized Ferrous iron (Fe2+) is again reduced to Iron ore (Fe0).
• The Ferrous iron (Fe2+) undergoes Ferrous iron oxidation by Bacterial or Chemical
oxidation process and results in formation of Ferric iron (Fe3+).
• Gallionella sp., Thiobacillus ferrooxidans, Sulfolobus sp., Iron bacteria (Sphaerotilus
sp. & Leptothrix sp.) and Dechlorosoma suillum

5. 2. FERROUS IRON REDUCTION
• The oxidized Ferric iron (Fe3+) is reduced to Ferrous iron (Fe2+) by Bacterial or Chemical reduction
process.
• Microorganisms involved in Ferric iron reduction process are Geobacter metallireducens, Geobacter
sulfurreducens, Ferribacterium limneticum, Shewanella putrefaciens and Aquaspirillum magnetotaticum.
• Ferric Iron Reduction is a Two steps process;
Ferric iron (Fe3+) is
reduced to Ferric
hydroxide (FeOH3)
Ferric hydroxide
(FeOH3) is
reduced to Ferrous
iron (Fe2+)

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