Iron Oxidizing Bacteria

• Iron Oxidizing Bacteria (IOB). These bacteria are known for producing mineral deposits that cover metal surfaces and provide better growth conditions for more corrosive bacteria like SRB. (Skovhus et al. 2017) Most of the members of this group catalyze the reaction of oxidizing ferrous iron (Fe²⁺) into ferric iron (Fe³⁺) in order to obtain energy. However, there are many subgroups of iron oxidizing bacteria based on oxygen availability and pH levels (how acidic their environment is).  The most relevant to the oil and gas industry are:

• Neutrophilic, micro-aerobic iron-oxidizers. This group often colonizes the interface between aerobic and anaerobic zones in sediments, and ground waters, which gives them the name of “gradient” organisms. Example of these organisms can be Gallionella spp. and Leptothrix spp. It had been recorded, that some iron-oxidizers can also “breathe” nitrate if oxygen is depleted from their environment.

• Acidophilic, aerobic iron-oxidizers. This group thrives in aerobic acidic environments and plays a significant role in catalyzing the production of acid mine drainage from metal and coal mines. New technologies have facilitated the use of some of these microorganisms into a new form of mining called biomining. (Hedrich et al. 2011) One of the most representative organisms from this group is Acidithiobacillus ferroxidans.