Microorganisms play a key role in transforming micronutrients in soil. Bacteria oxidize iron from the ferrous to the ferric state, precipitating it out as iron hydroxide. They also solubilize zinc, making it more available to plants. Various bacteria and fungi transform manganese and copper in the soil through oxidation and precipitation reactions. These microbial transformations influence the availability and forms of essential micronutrients for plant uptake.

1. Microbial Mediated
Micronutrient Transformation in
soil
Fe
Zn
Cu
Mo
Mn

2. • Plants require some elements in such minute or smaller
amounts that these element have been designated as
minor/trace element or Micro nutrient.
• Plants absorbed micronutrient in lower concentration ppm
level.
Micronutrient
Iron, Zinc, Copper, Manganese, Boron, Molybdenum, Nickel, Chloride

3. • Source- Goethite, Haematite, Magnetite, Limonite,
Olivine
• Forms of Fe- Ferrous & Ferric (Two oxidation state)
• Two fraction- Organic & mineral
• Sufficient range of Fe in plants : 50 – 250 ppm.
• Below 50 ppm – Deficiency appears young leaves-
Interveinal chlorosis.
• Above 250 ppm- Leaf bronzing.
Iron (Fe)

4. Fe in soil
Mineral Fe
• 4th most abundant element in earth crust 5%
• Solubility is low.
Soil solution
• Well drained , oxidised soil has a more Fe3+
• Water logged soil – More Fe2+

5. Iron bacteria (micro organisms) play a major role
in transformation
 Bacteria & fungi oxidise ferrous state to ferric
state.
Heterotrophic microorganism attacks soluble
organic Fe in to inorganic Fe salts.
Bacteria & fungi produce specific enzyme.
Transformation of iron in soil by
Micro organisms

6. Bacteria oxidise ferrous Fe to ferric Fe state which
precipitate as ferric hydroxide – Iron Bacteria
• Gallinonella
• Siderocapsa
• Siderosphaera
• Ferribacterium
• Naumanniela
• Sideromonas
• Ferro-bacillus
• Siderobacter
• Siderococus

7. • Obligate Chemoautotrophs- Capable of utilizing
energy released in the process of ferric hydroxide
formation.
(E.g) Gallionella ferruginea
Thiobacillus ferroxidans
Ferrobacillus ferroxidans
Classification

8. • Facultative Chemoautotrophs-Utilizing energy
derived in the process of ferric hydroxide formation
or from organic matter.
• (E,g) Leptothrix ochraceae
• Heterotrophs- Do not energy derived in the process
of ferric hydroxide formation but depend on
organic matter for nutrition.
• (E.g) Naumanniela

9. • Cyanophycea
• Volvocales
• Chlorococcales
• Eugleninaea
• Conjugales
Transform ferrous salts to ferric salt
Algae

11. • Source: Limestone, Sandstone.
• Forms: Zn2+
• Sufficient range of Zn in plants : 25 – 150 ppm
• Mineral: Zn in lithosphere is 80 ppm
• Soil solution: Depends on the soil pH . If pH is more
Zn2+ availability is more.
Zinc (Zn)

12. Two fraction
Organic- Small amount 0.01%- 0.05%
Inorganic- Source is Zinc sulphate- soluble in soil
Below and above the range cause Rosetting or clustering of
young leaves.
Young leaves become chlorotic spot.

13. • Omnipotent bacteria- Increase concentration of Zn
• Fungi also influence solubilize the mineral from of
Zn in soil by production of organic acids.
• Organic material increase the availability of micro
organisms in soil
• Increase the availability of Zn in soil
Transformation of Zinc in soil by
Micro organisms

14. • Several zinc solubilizing bacteria (ZSB)- Tropical
and temperate soils to provide plant available Zn.
(Hafeez et al., 2013).
• Gluconacetobacter – sugarcane.
• Bacillus, Pseudomonas - Soybean, rice and wheat
capable of solubilizing Zn. (Saravanan et al., 2011).
Omnipotent bacteria

15. Zinc solubilizing bacteria
• Pseudomonas
• Bacillus
• Gluconacetobacter
• Burkholderia
• Acinetobacter
• Serratia
• Flavobacter
• Enterobacter

16. Comparison
• ZSB
• ZSB soil bacteria,
able to solubilize the
inorganic Zn

17. • These ZSB strains produce variety of low molecular
weight organic acids, particularly gluconic acid,
dissolute the insoluble Zn
• Reduce the pH of the soil solution - increase the plant
available zinc (Hafeez et al., 2013).
• Zn-fertilizers - 1-5% use efficiency for most of the crops
• ZSB soil bacteria, able to solubilize the inorganic Zn and
thereby increase the bioavailability for crop assimilation.

18. • Source: Pyrolusite, Hausmannite, Manganite.
• Forms: Mn2+
• Sufficient range of plant: 20 – 500 ppm.
• Fraction: Solution, Exchangeable, Organic, Mineral
Manganese

19. Mineral Mn
• Mn is found in most Fe-Mg rocks- weathering of primary
mineral.
• Pyrolusite
• Manganite
Soil solution Mn:
• MnSO4 is the most common Mn sources in soil.
• Most common form Mn2+ - 90%.
• High pH- Solubility of Mn2+ is low

20. • Manganese transformation include bacteria, fungi and
yeasts.
• Bacteria – Leptothrix mobilis - aquatic environment-
oxidizing both iron, manganese. (Nelson et al. 1998)
• Oxidize manganous compounds to manganic oxides
(MnO.,) at pH values as low as 6 & some times below 6.
(Mulder 1964, Mulder and van Veen 1963).
Transformation of Manganese in soil
by Micro organisms

21. • Manganese oxidation by a mixture of two bacteria
Corynebacterium sp. Chromobacterium sp. has been
recorded by Bromfield and Skerman (1950)
• Roots of living plants may promote the solubilization of
MnO, by excreting organic acids or other compounds
stimulating bacterial activity.

22. • Source: Malachite, Cupric ferrite, Carbonates,
Silicates, Sulfates, Chlorides.
• Sufficient range in plants: 5 to 20 ppm.
• Forms: Cuprous (Cu+), Cupric (Cu2+)
Copper

23. • Availability of copper in soil related with the presence of
black organic humus.
• H2S forming microorganisms may be involved in copper
precipitation.
Transformation of Copper in soil by
Micro organisms

24. Copper precipitation by hydrogen-sulphide-
producing bacteria
• Clostridia, Proteus vulgaris, Escherichia coli - producing
H2S from sulphur-containing amino acids (cystine,
methionine, glutathion, etc.)- precipitate the Cu
• Sulphate-reducing bacteria- precipitate the Cu- Insoluble
form- Assimilatory sulfate reduction
• Sulfate-reducing bacteria are responsible - hydrogen
sulfide will react with metal ions to produce metal
sulphides. These metal sulphides- insoluble