Effect of thermophilic bacteria on the siliceous deposition and phylogenetic analysis of the bacterial diversity in silica scale

Silica scale, one of the major problems for geothermal power development, w as formed on the copper test plates in geothermal hot water (85+/-2 degrees C, pH 7.2). Numerous bacterial shaped structures were observed and mixed b acterial population of genomic DNA was stably extracted from the silica sca le. The amount of silica scale and extracted DNA increased exponentially wi th the time of incubation in the geothermal hot water. The molecular phyoge netic survey of extremely thermophilic bacterial diversities in silica scal e was carried out by using the PCR-mediated small subunit rRNA gene (rDNA) sequencing. The community was composed mainly of three phylogenetic types i n domain Bacteria. Cluster I was affiliated with the Aquificales and cluste r II was closely related to the genus Thermus. Cluster III was homologus wi th Gram-positive anaerobic thermophilic bacteria. These bacterial communiti es may possibly contribute to the rapid aggregation of silica.