Microbial participation in the formation of siliceous scale from geothermal waters and scale control

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1.Experiments of siliceous scale formation : Studies on siliceous deposits were carried out at the Otake geothermal power plant, Oita prefecture, Kyushu, Japan. Thin copper plates were immersed in the geothermal water of the aging tank, from June to December, 1994 and from September to December, 1995. Temperatures, pH and SiO2 content of the geothermal water were measured. The siliceous deposits grew cylindrically on the plate. The siliceous deposit on the plate was gently removed from the geothermal water and placed immediately in liquid nitrogen and stored at -20ﾟC until use.2.Mineralogical studies : The siliceous deposits were examined under the microscope and by X-ray diffraction analysis. The chemical composition was determined by X-ray fluorescence. Scale consists of namy mineral phases, which formed in situ, in the well head and in depth.3.Investigation of microbial participation : Numerousrod-shaped bacterial cells were observed in amorphous silica formed on the copper plate pl … More aced in geothermal hot water, under conditions of pH 7.2 and 85(]SY.+-。[)2ﾟC.(1) Bulk genomic DNA in the siliceous deposit could be stably extracted using the lysozyme and freeze-thaw method. The volume of siliceous deposit formed on one copper plate and the amount of genomic DNA extracted from siliceous deposits was exponentially increased with the time of incubation.(2) The phylogenetic diversity in these DNA extracts was investigated by cloning and sequencing of partial 16S rRNA genes obtained by PCR.The bacterial community was composed mainly of three phylogenetic types in domain Bacteria. Cluster I (8 clones) was affiliated with the Aquificales and Cluster II (15 clones) was closely related to genus Thermus. Cluster III (2 clones), the sequences of which were homologous with Gram positive anaerobic thermophilic bacteria, was also detected.4.These extremely thermophilic bacteria may contribute to the rapid aggregation of amorphous silica and can probably serve as a parameter to determine the rate formation of siliceous deposit in the process of biomineralization. Less