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Iron

Iron

Certain bacteria oxidize ferrous iron to ferric state which precipitate as ferric hydroxide around cells. These bacteria commonly known as iron bacteria B, C, D) are usually non-filamentous and spherical or rod-shaped (Gal­lionella, Siderophacus, Siderocapsa, Siderosphaera, Ferribacterium, Naumanniela, Ochrobium, Sideromonas, Sideronema, Ferrobacillus, Siderobacter and Siderococ­cus).

Filamentous forms resembling algae are also encountered (Leptothrix, Sphaerotilus, Toxothrix, Crenothrix and Colnothrix). In addition to these bacteria, certain algae belonging to Cyanophycea, Volvocales, Chlorococcales, Euglenineae, Conjugales and Ulotrichales also transform ferrous salts to ferric state and deposit the precipitation around the filaments. The ferric hydroxide deposits give a brown or rust-red colour to these organisms.

The iron bacteria can be grouped into: (1) obligate chemoautotrophs, capable of utilizing energy released in the process of ferric hydroxide for­mation (Gallionella ferruginea, Thiobacillus ferroxidans and Ferrobacillus fer­roxidans), (2) facultative chemoautotrophs, utilizing energy derived in the process of ferric hydroxide formation or alternatively, from organic matter (Leptothrix ochraceae) and

(3) heterotrophs represented by most other iron bacteria which do not derive energy from iron oxidation but depend on organic matter for their nutrition. The iron bacteria play no significant role in cultivable soils and hence their importance in plant-microorganisms in­teraction, barring indirect effects, is less noteworthy.
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