Induced transformation of amorphous silica to cristobalite on bacterial surfaces

Extreme conditions such as high temperature and/or pressure are usually required for the transformation of amorphous silica to crystalline polymorphs. In this article, we present our results that amorphous silica can be deposited on a bacterial surface and transformed to cristobalite at a relatively low temperature and ambient pressure. The phase transformation of amorphous silica to cristobalite under thermal treatment was investigated by a variety of methods including X-ray diffraction, electron microscopy, and Fourier transform infrared spectroscopy. Results show that amorphous silica on a bacterial cell surface exhibits a direct phase transformation to cristobalite structure at a relatively low temperature (800°C). The surface charge of the bacterial cells does not affect the phase transformation. Three Gram-negative bacteria and three Gram-positive bacteria have been tested in the present study. All these bacteria have been found to facilitate the phase transition of amorphous silica into cristobalite. The observation of amorphous silica transformation on bacterial surfaces to cristobalite highlights the use of bacteria in the synthesis and structure control of silica minerals.