Biogenic Silica Deposition in Geothermal Hot Water

Abstract

Current observations of geothermal and hydrothermal deposits have suggested that a variety of thermophilic or hyperthermophilic microorganisms living under such extreme conditions are likely to be associated with the rapid formation of siliceous deposits from hot waters. Cultureindependent molecular ecological studies revealed that the extremely thermophilic microbial population was consistently present in silica scales formed in the aging tank at the Japanese geothermal power plant and the genera Thermus and Hydrogenobacter were predominant microbial components in the siliceous deposits. Culture-dependent in vitro analyses using the Thermus cells indicated that the cell growth caused the rapid precipitation of supersaturated amorphous silica and concomitantly produced a specific cell envelope protein, we called 'Sip (silica induced protein)'. Our study implicates that microorganisms may utilize the dissolved supersaturated amorphous silica for the maintenance of position and survival in limited niches in geothermal hot water environments.