Interfacial Energetics of Bacterial Silicification

Abstract

Silica nanoparticle size distributions were measured from transmission electron micrographs of bacterial cells in thin-sectioned hot spring sediment samples, as well as specimens from laboratory experiments on bacterial silicification. Diameters of silica nanoparticles on bacterial cells were smaller than corresponding values of those occurring away from bacteria in the same fields of view. Regression analysis of the particle size data and application of the Lifshitz-van der Waals Acid-Base approach to evaluations of solid surface energy established that the size difference extends from a nearly 40% decrease in the mean interfacial energy of silica nanoparticles on bacteria (0.9 mJ/m ² ) as opposed to free in aqueous suspension (1.2 mJ/m ² ). In thermodynamic terms, the lower interfacial energy serves to reduce equilibrium solubility values, and enhance nucleation rates, of silica nanoparticles on bacteria cells. The well documented culmination of these events in hot spring sediments and experimental studies is rapid preferential silicification and structural preservation of bacterial cells.

Keywords:

• silicification
• silica
• bacteria
• microfossils
• nucleation

Acknowledgments

This work was supported by the Natural Science and Engineering Council (NSERC) of Canada.

Notes

*Cyanidium Creek and Porkchop Pool are in Yellowstone National Park, Wyoming, U.S.A (Ferris et al. 1986); Geysir, Iceland (SchultzeLam et al. 1995); El Taito, Chile (Phoenix et al. 2006); Silica 30, 60, and 150 are from laboratory experiments (Ferris et al. 1988)