Microbe-related precipitation of iron and silica in the Edmond deep-sea hydrothermal vent field on the Central Indian Ridge

Abstract

Microbial mats, several millimeters thick and brown-yellow to white in color, were collected in hollow inside of chimney structure from Edmond hydrothermal field on the Central Indian Ridge. Microbes with shapes of rod and helical stalk-like filaments were observed in the microbial mats, and are commonly characterized by their cells completely encrusted by thick mineralized layers, made up of large amounts of amorphous silica and minor amounts of iron oxides. Transmission Electron Microscope observation has demonstrated that the acicular Fe-bearing matter was not only heterogenously distributed on the surface of the cell wall, but also deposited in the inside of cell, suggesting that bio-precipitation of Fe had occurred both on the surface and in the interior of cell. Microbial silicification was also commonly found in the mats. Silica usually precipitated homogeneously on the surface of the microbes and forms micro-laminated layers, which might be controlled by the inorganic process of precipitation in hydrothermal environment. The biomineralization phenomenon in the microbial mats showed that the precipitation of Fe and Si was closely related to microbes in hydrothermal environment. Considering that hydrothermal activities provided required chemical elements for mineralization, it is suggested that this biomineralization process also might be driven by hydrothermal activities at the sea floor to some extent.