30th Annual SSRL Users' Meeting — October 9-10, 2003

Microbial Polymer Templation of Iron Oxyhydroxides

C. S. Chan,1 S. Fakra,2 G. De Stasio,3 S. A. Welch,4 and J. F. Banfield1

1Department of Earth and Planetary Science, University of California at Berkeley, Berkeley, CA 94720 USA
2Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA
3Department of Physics, University of Wisconsin, Madison, WI 53706 USA
4CRC-LEME, The Australian National University, Canberra ACT 0200 Australia

Biopolymers have been shown to control the nucleation, orientation, and growth of crystals. Microbial mineralization can have a significant effect on environmental chemistry by producing minerals with phases, morphologies, and reactivities that differ from inorganically precipitated minerals.

We have found evidence of a novel form of polymer-assisted biomineralization: extremely thin (few-unit cell wide), microns-long akaganeite (-FeOOH) filaments that are templated on natural microbial polymer fibrils. These filaments were identified in iron oxide-encrusted biofilm samples in the flooded Piquette Mine, WI, USA using high resolution transmission electron microscopy. These pseudo-single crystals are composed of assembled elongate nanocrystals oriented end-to-end in the [010] direction. The presence of akaganeite is unusual, since it is generally considered to form in high salinity environments, suggesting that polymer templation has altered iron oxide phase stability.

In order to verify the presence of the polymer, filaments in biofilm samples were imaged by synchrotron X-ray photoelectron emission microscopy (PEEM; performed at the Synchrotron Radiation Center, University of Wisconsin) and scanning transmission X-ray microscopy (STXM; performed at the Advanced Light Source, Lawrence Berkeley National Laboratory). The carbon 1s X-ray absorption near edge spectra of the filaments confirm the presence of organic polymer, including polysaccharide and possibly protein. To test the hypothesis that polymer fibrils can template akaganeite filament formation, we have been performing experiments to simulate the postulated mineralization pathway. Initial analyses of these samples by STXM has yielded preliminary information about the molecular interactions between polysaccharides and iron.

These experiments show the utility of synchrotron-based X-ray spectromicroscopy in biomineralization studies.