Formation of Fe-silicates and Fe-oxides on bacterial surfaces in samples collected near hydrothermal vents on the Southern Explorer Ridge in the northeast Pacific Ocean

Samples collected in low-temperature (2-50 degrees C) waters near hydrother mal vents of the Southern Explorer Ridge, in the northeast Pacific Ocean, c ontained fine (<500 nm) Fe- and Mn-oxide and Fe-silicate particles coating bacterial surfaces. Partially to totally mineralized bacteria, along with b acterial exopolymers, were covered with a mixture of poorly ordered Si-rich Fe-oxides (possibly ferrihydrite), Mn-oxides, and Fe-silicates (possibly n ontronite). Minerals occur as very fine (2-20 nm) granular material, fine ( 20-100 nm) needles and sheets, small (200-500 nm) nodules and filaments (i. e., mineralized exopolymers). Under saturation conditions, we infer that ba cterial surfaces provided nucleation sites for poorly ordered oxides and si licates. The formation of Fe- and Mn-oxides was likely initiated by the dir ect binding of soluble Fe and Mn species to reactive sites (like carboxyl, phosphate, and hydroxyl groups) present within the bacterial cell wall and the exopolymers. Fe-silicate formation involved a more complex binding mech anism, whereas metal ions, such as Fe, possibly bridged reactive sites with in the cell walls to silicate anions to initiate silicate nucleation.