2001 Volume 16 Issue 2 Pages 125-130
At Steep Cone hot spring, Lower Geyser Basin, Yellowstone National Park, a mound of siliceous deposits called "siliceous sinter" forms from discharged boiling geothermal water that is supersaturated with amorphous silica. Electron-probe microanalyzer (EPMA) observations suggested that silica is deposited on the surface of the cells and that microorganisms affect the formation of the siliceous sinter. EPMA signals and backscattered electron images of sinter samples taken at the inner wall of the boiling pool revealed framboidal pyrite structures associated with a network of silicified microbial structures. The structure of bacterial community in a beige-colored sinter sediment (75.8°C, pH 8.6) was studied by molecular clone type phylogenetic analysis of PCR-mediated 16S rDNA fragments. The bacterial rDNA clones found indicated the presence of a complex community in the sinter sediment. Sequences closely related to the genera Thermus and Saccharomonospora were dominated; evidence of indigenous microbial components.