Microbial Ion Accumulation and Mineral Formation in the Weathering Environment

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Bacteria are the earlist life of the Earth, appearing within the first billion years of the Earth's history. Scince then, bacteria have been widely distributed on the Earth's surface including soils, weathered rocks and sediments, lakes, rivers, and oceans. Geobiological studies have shown that bacteria play an important role in elemental circulation over the Earth's surface, especially through the interactions of cell wall surfaces with dissolved ions in the external environments producing various secondary minerals such asoxides, sulfides, carbonates, and silicates. This study focused on such bacteria - mineral interaction in various weathered sediments (Ito pyroclastic fllow deposit, Akahoya volcanic ash deposit, Kaimondake volcanic ash deposit, Sakurajima volcanic ash deposit) distributed in Kagoshima prefecture, Southern Kyushu, Japan, using XRD, SEM, TEM, and EDX. Results of this study indicated that these weathered sediments contain great amounts of spherical to rod-shaped bacteria (10^7〜10^8 cells/g) covered or decorated with poorly ordered secondary minerals exhibiting aggregates of fine fibrous materials. EDX confirmed that the secondary minerals consisted mainly of Al, Si, and Fe, corresponding to chemical compositions among allophane, nontronite, and chamosite. These chemical characteristics are apparently different from those of abiogenie secondary products such as allophane and halloysite co-existing with the products on the bacterial surfaces. This strongly indicates that the most of bacteria in the weathered sediments acculucate Al, Si, and Fe ions and produce silicate minerals on their cell surfaces.