Rapid in situ silicification of microbes at Loburu hot springs, Lake Bogoria, Kenya Rift Valley

Abstract

Microbial mats, located along the margins of hot-spring pools and out¯ow channels at Lake Bogoria, Kenya, are commonly silici®ed forming friable laminated crusts. Columnar microstromatolites composed of silica and calcite are also forming at several springs in sites of oscillating water level or spray. Silici®cation of the microbes involves impregnation of organic tissue by very ®ne amorphous silica particles and encrustation by small (< 2 lm) silica spheroids. Rapid silici®cation of the microbes, which may begin while some are still alive, can preserve sheaths and in some examples, the ®laments, capsules and cells. Although this provides evidence of their general morphology, the biological features that are required for taxonomic identi®cations are commonly poorly preserved.The silica precipitation results mainly from evaporative concentration and rapid cooling of spring waters that have been drawn upward through the mats and microstromatolites by capillary processes. Almost all the silica at the Loburu springs nucleates on microbial substrates. This af®nity of silica for functional groups on microbial surfaces contributes to the rapid silici®cation of the microbes and their preservation in modern and ancient cherts.

Evidence of microbiologic activity in modern travertines: Sicakcermik geothermal field, central Turkey

“…Thereare severaltypesof organic deposits in the geothermal field of Sicakeermik as described by Risacher and Eugster (1979), Chafetz and Butler (1980), Meredith (1980), Schreiber et al (1981), Chafetz and Meredith(1983), Chafetz and Folk (1984), Love and Chafetz (1988), Guo and Riding (1992, 1994, 1998, Renaut et al (1998), and Chafetz and Iron -and manganese -rich shrubfabrics form on low -angle slopesin microfalls/microcascades as wellas at the edgesof microterraces. Shrub fabrics can be considered somewhat equivalent to "fossil bacteria stromatolithes" described by Walter (1976).…”

Silica Biomineralization of Unicellular Microbes Under Strongly Acidic Conditions

“…The cell walls of microbes generally include, more or less, polysaccharides and proteins, and have an affinity for silica (e.g., Renaut et al 1998). Mizutani et al (1998) also reported that amines, notably polyamine, catalyze the polycondensation of silicic acid in water.…”

“…In order to understand silica control by the microbes, it is important to investigate silicification of unicellular cells. It is also necessary to look for a modern-day aqueous surface-environment where unicellular microbes undergo silicification (Renaut et al 1998, Asada & Tazaki 1999. In some examples of hydrothermal systems, such as terrestrial hot-springs and hydrothermal vents on the seafloor, silica precipitation occurs (Tazaki et al 1996, Tazaki 1999b, Shikaura et al 1999, Yamamura et al 1997.…”

“…Almost all the silica at Loburu Springs, Kenya, nucleated on microbial substrates; nucleation was facilitated by the affinity of silica for functional groups on microbial surfaces (Renaut et al 1998). These processes of biomineralization contributed to the rapid silicification of the microbes and to their preservation in modern and ancient cherts.…”

Calcification and Silicification: Fossilization Potential of Cyanobacteria from Stromatolites of Niuafo‘ou's Caldera Lakes (Tonga) and Implications for the Early Fossil Record

“…Similar spectacularly preserved silicified microbes, including cyanobacteria, are known from modern hot spring environments. In this case, the rapidly silicified microorganisms are preserved with their morphology, diameter, length, and some inner structures, such as remains of cytoplasm and intercellular septation (e.g., Cady and Farmer, 1996;Renaut et al, 1998;Jones et al, 2004). Also, fossil analogues of modern siliceous thermal spring sinters, like the Devonian Rhynie chert (Scotland), enclose cellularly preserved microorganisms (Trewin, 1994(Trewin, , 1996Cady and Farmer, 1996;Preston and Genge, 2010).…”