The influence of extracellular superoxide on iron redox chemistry and bioavailability to aquatic microorganisms.

Andrew L Rose

doi:10.3389/fmicb.2012.00124

Abstract

Superoxide, the one-electron reduced form of dioxygen, is produced in the extracellular milieu of aquatic microbes through a range of abiotic chemical processes and also by microbes themselves. Due to its ability to promote both oxidative and reductive reactions, superoxide may have a profound impact on the redox state of iron, potentially influencing iron solubility, complex speciation, and bioavailability. The interplay between iron, superoxide, and oxygen may also produce a cascade of other highly reactive transients in oxygenated natural waters. For microbes, the overall effect of reactions between superoxide and iron may be deleterious or beneficial, depending on the organism and its chemical environment. Here I critically discuss recent advances in understanding: (i) sources of extracellular superoxide in natural waters, with a particular emphasis on microbial generation; (ii) the chemistry of reactions between superoxide and iron; and (iii) the influence of these processes on iron bioavailability and microbial iron nutrition.

Highlights

Superoxide (O−2 ), an anion resulting from the transfer of oneelectron to a molecule of oxygen, was first identified by EdwardNeuman, a postdoctoral researcher working with Linus Pauling, in 1934 (Neuman, 1934) as part of Pauling’s ongoing interest in the nature of the chemical bond (Pauling, 1979)
(Rose et al, 2008b, 2010; Hansard et al, 2010; Shaked et al, 2010). These lifetimes are sufficiently long to ensure that O−2 ∗ can diffuse well away from the site of its production, enabling it to influence local redox chemistry on a spatial scale that is biologically significant, while typical concentrations are sufficiently high to ensure that it can react at environmentally relevant rates
The primary purpose of this paper is to provide a detailed overview of the ways in which O−2 ∗ in the external milieu of microorganisms can modulate the chemical speciation of Fe, and thereby influence its biological availability

Summary

Introduction

Superoxide (O−2 ), an anion resulting from the transfer of oneelectron to a molecule of oxygen, was first identified by EdwardNeuman, a postdoctoral researcher working with Linus Pauling, in 1934 (Neuman, 1934) as part of Pauling’s ongoing interest in the nature of the chemical bond (Pauling, 1979). It is only since the 1980s that the potential role of O−2 ∗ in the aqueous extracellular environment has been examined in detail. Baxter and Carey (1983) established that O−2 ∗ was formed www.frontiersin.org

Objectives

Conclusion