Freshwater Ferromanganese Stromatolites from Lake Vermilion, Minnesota: Microbial Culturing and Environmental Scanning Electron Microscopy Investigations

Abstract

Lacustrine ferromanganese oxide nodules have been discovered in Lake Vermilion, northern Minnesota, USA. They occur as two morphotypes: laminated discs growing around or on cobbles ("reef-type"), and ovoid nodules on muddy gravel ("oncoidtype"). Nodules have only been found within a depth-range of »1 to 7 m, and no nodules were found on or in ne mud sediments. Oxide coatings on recent litter allowed estimates of growth rates between 2.3 to 3.5 ¹m/yr. X-ray diffraction, energy dispersive X-ray spectroscopy, and thin section and environmental scanning electron microscopy of the nodules showed microorganisms, chie y bacteria but also including cyanobacteria, diatoms, and other protozoans, mineralized by X-ray amorphous ferromanganese oxyhydroxide compounds and forming porous granular layers. ESEM examination also revealed solid-appearing layers, with no microorganism remains. Bacterial culturing experiments were carried out using lake water, sediment, and nodule swabs and pieces as the inocula. All resulted in the growth of bacteria that reduce and/or oxidize iron and manganese, showing that metal oxidizing and reducing bacteria are ubiquitous within the lake habitats. The culturing experiments also demonstrate that the bacteria can cause the formation of solid metal oxides. The combination of culturing and ESEM

Geomicrobiology of Iron Layers in the Sediment of Lake Superior

“…The distribution of all metabolic groups, such as chemotrophic, mixotrophic, and lithotrophic denitrifiers, as well as denitrifiers capable of aerobic iron oxidation throughout the upper sediment layers was relatively uniform (Hauck et al 2001), leading to the conclusion that no specific microbial metabolism could be linked to Fe-rich layers in Lake Constance. In oligotrophic Lake Vermilion (USA), ferromanganese nodules were found near the sediment surface, similar to nodules found in other lakes around the globe (see references in Sommers et al 2002). The nodules consisted of laminated layers enriched in Mn and Fe, and differed in size and morphology.…”

Accretion of ferromanganese nodules that form pavement in Second Connecticut Lake, New Hampshire

“…Lacustrine nodules differ in size (mm to cm) and morphology (mound, flat, and ovoid) (1,4). Elemental composition also varies between lake systems, within the same lake, and even within an individual nodule in the same lake, particularly with respect to Fe:Mn ratios (2,4,6).…”

“…However, direct evidence of microbial activity in and on their surface leads to names such as stromatolites, microbialites, or even oncoids (4, 7). Rod and coccoid bacteria are reported to catalyze the precipitation of Fe and Mn oxides (4,(8)(9)(10). This microbial precipitation occurs 60 times faster than abiotic processes under comparable environmental conditions (5,11).…”

“…Elemental composition also varies between lake systems, within the same lake, and even within an individual nodule in the same lake, particularly with respect to Fe:Mn ratios (2,4,6). Elemental concentration may control the nodule morphology (12).…”

“…Elemental concentration may control the nodule morphology (12). Barium (Ba), nickel (Ni), copper (Cu), zinc (Zn), and lead (Pb) elements present in freshwater nodules (4,13) are usable as catalysts in the oxidation and reduction of both major metals (e.g., Fe or Mn) (8,9). Moreover, ferromanganese nodules have been economically important to humans since ancient times as sources of Mn oxides and their coprecipitates (Cu, Ni, and Co) (5,14).…”