Microbial Oxidation of Fe(II) and Mn(II) at Circumneutral pH

David Emerson

doi:10.1128/9781555818098.ch2

Chapter 2 : Microbial Oxidation of Fe(II) and Mn(II) at Circumneutral pH

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Affiliations: 1: American Type Culture Collection, 10801 University Blvd., and Institute for Biosciences, Bioinformatics, and Biotechnology, George Mason University, Manassas, VA 20110

Content Type: Monograph

Publication Year: 2000

Category: Environmental Microbiology

Book DOI: 10.1128/9781555818098

Chapter DOI: 10.1128/9781555818098.ch2

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Abstract:

Over the past decade it has become clear that iron and manganese can be important electron acceptors for anaerobic respiration carried out by a diverse array of prokaryotes. This chapter is biased toward iron, in part because a number of recent findings concerning the role of microbes in iron (Fe) oxidation make this area of particular interest at the organismal level and in part because an excellent review on manganese (Mn) oxidation was recently published. It is also biased toward organisms rather than molecules, since virtually nothing is know about the molecules, involved in Fe oxidation at neutral pH, although there is an emerging story in this regard concerning Mn. In terms of biological reactivity, the two most relevant oxidation states of iron are Fe(II), the reduced ferrous form, and Fe(III), the oxidized ferric form. To illustrate the commonalities and differences that are manifested by the sites, four quite different examples are discussed. The examples are Marselisborg, Loihi, Plant Rhizosphere, and Anaerobic Environments. Representatives of some of the Fe oxidizers that are known to occur in the habitats are discussed in detail in this chapter. The oxidation of the manganous ion, Mn(II), to the manganic form, Mn(IV), is a two-electron transfer, which can proceed via one-electron steps through an unstable intermediate, Mn(III). Examples of three quite different Mn-oxidizing organisms are discussed in detail. The three Mn-oxidizing organisms are L. discophora, Marine Bacillus sp. strain SG-1, and Metallogenium.

Citation: Emerson D. 2000. Microbial Oxidation of Fe(II) and Mn(II) at Circumneutral pH, p 31-52. In Lovley D (ed), Environmental Microbe-Metal Interactions. ASM Press, Washington, DC. doi: 10.1128/9781555818098.ch2

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Microbial Oxidation of Fe(II) and Mn(II) at Circumneutral pH

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Figure 1

Phase contrast light micrographs of iron oxides from environmental samples. (A) Sample from a circumneutral iron spring in Northern Virginia. The arrows denote L. ochracea-like sheaths. Note also the presence of finer filaments of Fe oxides that are of unknown origin, as well as the larger amorphous particles of Fe oxides. Bar, 10 μm. (B) Sample collected from an iron-rich hydrothermal vent site on the North Gorda Ridge in the Pacific Ocean. The arrows again denote the remains of L. ochracea-like sheath structures. Bar, 20 μm.

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Figure 2

Transmission electron micrographs of Fe-oxidizing bacteria from the Marselisborg iron seep. (A) L. ochracea ensheathed cell and empty sheath in cross-section. Note the thick Fe oxide crust on the sheath. Bar, 0.5 μm. (A) G. ferruginea. The arrow points to a portion of the stalk that is attached to the cell. Bar, 0.5 μm.

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Figure 3

Anaerobic growth of F. placidus on iron and nitrate under chemolithoau-totrophic conditions. Symbols: ■, ferric iron in growing culture, ○, autoxidation in uninoculated culture medium at 85°C, ●, nitrate in growing culture, ▲, number of cells per milliliter. Reprinted from reference 36 with permission of the publisher.

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