Geomicrobiology of manganese

It is difcult to discuss the manganese (Mn) cycle in isolation. Manganese is inherently and indiscriminately interactive due to the unique geochemical characteristics of the various Mn species. The redox cycling of Mn involves a Mn(II) antioxidant and both a Mn(III) reactive intermediate and Mn(III, IV) oxide mineral, two of the strongest oxidants on our planet. Further, the immense reactivity of Mn oxides is responsible for their role and utility as environmental sponges (Figure 18.1). Indeed, the cycling of Mn comes to bear on nearly all other elemental cycles (spanning nutrients to radionuclides), touches every possible ecological niche (from the soils to the deep ocean and even below), and involves all domains of life (from bacteria to fungi). It must be inferred from the widespread occurrence of manganese-oxidizing and manganese-reducing microorganisms in terrestrial, freshwater, and marine systems that they play an essential role in the cycling of manganese, and therefore, by extension, environmental biogeochemistry in general. Though in no way comprehensive (we refer the reader to many informative reviewse.g., Nealson and Saffarini, 1994; Tebo et al., 1997; Post, 1999; Morgan, 2000; Tebo et al., 2004; Caneld et al., 2005; Lovley, 2006; Gadd, 2007; Spiro et al., 2010), this chapter attempts to tell the story of Mn, a story that spans the biological, chemical, and geological sciences.