View source for Mechanisms of Microbial Iron Reduction in Sediments

== Introduction ==

Microbial iron reduction is a critical [[Geochemical|geochemical]] process that occurs in a variety of [[Sediment|sedimentary]] environments. This process, carried out by iron-reducing bacteria, plays a significant role in the global iron cycle and has implications for other biogeochemical cycles, including those of carbon and sulfur. 

[[Image:Detail-38731.jpg|thumb|center|A close-up view of sediment layers, showing the different colors and textures that indicate various levels of iron content.|class=only_on_mobile]]
[[Image:Detail-38732.jpg|thumb|center|A close-up view of sediment layers, showing the different colors and textures that indicate various levels of iron content.|class=only_on_desktop]]

== Iron-Reducing Bacteria ==

Iron-reducing bacteria are a diverse group of microorganisms capable of using ferric iron (Fe(III)) as an electron acceptor in their metabolic processes. These bacteria, which include species from the genera [[Geobacter|Geobacter]], [[Shewanella|Shewanella]], and [[Desulfuromonas|Desulfuromonas]], can thrive in environments where oxygen, a more favorable electron acceptor, is limited or absent. 

== Mechanisms of Iron Reduction ==

Iron-reducing bacteria employ several mechanisms to reduce Fe(III) to ferrous iron (Fe(II)). These mechanisms can be broadly classified into direct and indirect reduction processes.

=== Direct Reduction ===

In direct reduction, the bacteria reduce Fe(III) through physical contact with iron minerals. This process involves the transfer of electrons from the bacterial cell to the iron mineral via c-type cytochromes, proteins that are located on the cell membrane and have the ability to bind and reduce Fe(III).

=== Indirect Reduction ===

Indirect reduction, on the other hand, involves the production of soluble electron shuttles or iron chelators that can reduce Fe(III) without the need for physical contact between the bacteria and the iron mineral. These compounds, which include flavins and phenazines, can diffuse through the sediment and reduce Fe(III) at a distance from the bacterial cell.

== Role in Biogeochemical Cycles ==

Microbial iron reduction has significant implications for several biogeochemical cycles. 

=== Carbon Cycle ===

In the carbon cycle, iron-reducing bacteria contribute to the decomposition of organic matter in sediments by using the organic compounds as electron donors in their metabolic processes. This results in the production of carbon dioxide, a key component of the carbon cycle.

=== Sulfur Cycle ===

In the sulfur cycle, the reduction of Fe(III) can influence the availability of sulfate, a compound that is used by sulfate-reducing bacteria as an electron acceptor. By competing with these bacteria for organic electron donors, iron-reducing bacteria can limit the extent of sulfate reduction and thus influence the cycling of sulfur in sediments.

== Environmental Implications ==

Microbial iron reduction has several environmental implications. For instance, the process can influence the mobility of trace metals and nutrients in sediments, as these compounds can be adsorbed onto iron minerals and released upon reduction. Furthermore, the production of Fe(II) through microbial iron reduction can lead to the formation of magnetite, a magnetic mineral that can influence the magnetic properties of sediments.

== See Also ==

* [[Geomicrobiology]]
* [[Redox]]
* [[Biogeochemistry]]

[[Category:Geomicrobiology]]
[[Category:Geochemistry]]
[[Category:Microbiology]]
[[Category:random]]