Iron–silica-rich low-temperature hydrothermal precipitates were collected from the CDE hydrothermal field located at the East Lau Spreading Center. Phylogenetic analysis showed that the precipitates were dominated by the members of α-proteobacteria and marine group I archaea. Ultrastructural analysis suggested the bacteriogenic origin of the iron–silica-rich deposits. Distinctive biosignatures detected included straight filaments, helical stalks and curved irregular filaments, which were similar in appearance to those structures excreted by the known iron-oxidizing genera Leptothrix spp., Gallionella spp. and Mariprofundus spp. 16S rRNA gene analysis confirmed the presence of neutrophilic iron-oxidizing bacteria with the detection of phylotypes clustering with Gallionella spp. and the proposed ζ-proteobacteria class. Mineralogy and bulk geochemical analyses showed that the precipitates were dominated by amorphous silica with low amounts of iron. Based on microbiological, geochemical and mineralogical analyses, we conclude that silicification was a common process and microbial cells and related ultrastructures likely acted as nucleation templates for silica precipitation in the CDE hydrothermal field.
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