Unravelling the microbial role in ooid formation – results of an in situ experiment in modern freshwater Lake Geneva in Switzerland

Abstract

The microbial role in the formation of the cortex of low‐Mg calcite freshwater ooids in western part of Lake Geneva in Switzerland has been suggested previously, but not demonstrated conclusively. Early work mostly concentrated in hypersaline milieus, and hence little is known about their genesis in freshwater environments. We designed an in situ experiment to mimic the natural process of low‐Mg calcite precipitation. A special device was placed in the ooid‐rich bank of the lake. It contained frosted glass (SiO2) slides, while quartz (SiO2) is the most abundant mineral composition of ooid nuclei that acted as artificial substrates to favour microbial colonization. Microscopic inspection of the slides revealed a clear seasonal pattern of carbonate precipitates, which were always closely associated with biofilms that developed on the surface of the frosted slides containing extracellular polymeric substance, coccoid and filamentous cyanobacteria, diatoms and heterotrophic bacteria. Carbonate precipitation peaks during early spring and late summer, and low‐Mg calcite crystals mostly occur in close association with filamentous and coccoid cyanobacteria (e.g. Tolypothrix, Oscillatoria and Synechococcus, Anacystis, respectively). Further scanning electron microscope inspection of the samples revealed low‐Mg calcite with crystal forms varying from anhedral to euhedral rhombohedra, depending on the seasons. Liquid cultures corroborate the in situ observations and demonstrate that under the same physicochemical conditions the absence of biofilms prevents the precipitation of low‐Mg calcite crystals. These results illustrate that biofilms play a substantial role in low‐Mg calcite ooid cortex formation. It further demonstrates the involvement of microbes in the early stages of ooid development. Combined with ongoing microbial cultures under laboratory‐controlled conditions, the outcome of our investigation favoured the hypothesis of external microbial precipitation of low‐Mg calcite as the main mechanism involved in the early stage of ooid formation in freshwater Lake Geneva.

Reversed Crystal Growth of Calcite in Naturally Occurring Travertine Crust

“…These microorganisms are embedded in their self-produced matrix of EPS. The bioactivities of the biofilm were found to be crucial, as its absence has been known to prevent the precipitation of low Mg-calcite [13]. To help explain the CaCO 3 precipitation processes associated with freshwater microbial biofilms, Pedley set up at non-invasive flowing water experimental mesocosm, run under near-natural conditions for a period of 2.5 years [14].…”

Preliminary investigations on picoplankton-related precipitation of alkaline-earth metal carbonates in meso-oligotrophic lake Geneva (Switzerland)

“…This study is part of a series of geomicrobiological analyses conducted in lake Geneva (Jaquet et al, 1982;Plée et al, 2008;Glas-Haller, 2010).…”

“…Various strains of Synechococcus have been tested for their potential to sequestrate atmospheric CO 2 (Lee et al, 2006;Jansson and Northen, 2010). This genus has also been found to be active in calcite ooid formation in western lake Geneva (Plée et al, 2008), closely associated to biofilms.…”

Present and future of subsurface biosphere studies in lacustrine sediments through scientific drilling

“…DAPI (4′,6-diamidino-2-phenylindole) microphotograph depicting active microbes in the water column of Lake Grosse Fuchkuhle in Germany; 2. Active photosynthetic microbes under natural light in shallow areas of western Lake Geneva, Switzerland, and SEM microphotographs of carbonate precipitates in the same area of the lake (Plee et al 2008); 3. Active microbes (Beggiatoa) in the water/sediment interface of Lake Geneva, Switzerland; and 4.…”

“…2, 2). This process is recorded as calcified filaments embedded in extracellular polymeric substance or EPS (Plee et al 2008). The sources of energy necessary for microbial survival change while moving toward aphotic zones where chemical reactions become critical in their fight for survival (Fig.…”