Iron-Oxidizing Bacteria Requiring No Oxygen

One of the bacteria classified into the purple bacteria group has been known to oxidize photosynthetically ferrous carbonate and ferrous sulfide to ferric hydroxide, resulting in the production of organic compounds [reactions (5.10) and (5.11)] (Ehrenreich and Widdel, 1994). Then ferric hydroxide is changed to iron (III) oxide. 

Chlorobium ferrooxidans, a green sulfur phototrophic bacterium, also oxidizes ferrous carbonate anaerobically to ferric hydroxide utilizing light energy, and produces organic compounds and carbon dioxide if a Geospirillum-like, bacterium co-resides [reaction (5.12)] (Heising et al., 1999). 

Furthermore, a bacterium has been found that oxidizes ferrous compounds to ferric hydroxide with nitrate and produces nitrite, hydrogen carbonate ion, and proton [reaction (5.13)]. The bacterium is called Ferroglobus placidus, an archaeon growing at 65-95°C (Hafenbradl et al., 1996). This bacterium thus produces ferric hydroxide without molecular oxygen or light. 

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