HR: 0800h
AN: B21B-0881    [Abstracts]
TI: Iron oxyhydroxide mineralization by microbes in terrestrial environments
AU: * Chan, C S
EM: chan@eps.berkeley.edu
AF: Dept. of Earth and Planetary Sci., 307 McCone Hall, Berkeley, CA 94618 United States
AU: Fakra, S
EM: sfakra@lbl.gov
AF: Advanced Light Source, Lawrence Berkeley Natl. Lab, 1 Cyclotron Rd. MS 2-400, Berkeley, CA 94720 United States
AU: Banfield, J F
EM: jill@eps.berkeley.edu
AF: Depts. of Earth and Planetary Sci. and Env. Sci. Policy and Management, 307 McCone Hall, Berkeley, CA 94618 United States
AB: Many microorganisms produce extracellular organic structures that become mineralized and thus preserved. As in higher organism mineralization (e.g. shells and bones), organics template mineral nucleation and control growth. However, polymer-mediated crystal growth is a more general phenomenon that can occur in extracellular, geochemically open systems. We have been studying microbial polymers mineralized by iron oxyhydroxides in a variety of natural environments, including a flooded mine in Wisconsin, creeks in Virginia and California, and cold springs in Oregon. Enrichment culturing showed that these environments are all populated by neutrophilic iron-oxidizers. We used scanning and transmission electron microscopy (SEM and TEM), Fourier transform infrared spectroscopy (FTIR), and synchrotron-based scanning transmission X-ray microscopy (STXM) to investigate the mineralogy and organic polymer functional groups. Microscopic observations revealed that these samples, while often dominated by the sheaths and stalks generally attributed to Leptothrix spp. and Gallionella, actually contain mineralized structures with a wide range of morphologies. The extent of mineralization is variable, with some environments characterized by heavy encrustations that likely formed via abiotic precipitation. We focused on the lightly mineralized polymers as this allows us to more closely examine the organic-mineral interactions. STXM work shows that the organics in the flooded mine and Virginia creek have common functional groups, including carboxyls. However, the exact ratio of functional groups may be more dependent on environmental factors than species. Our previous work showed that organic polymer fibrils template unusually long akaganeite (beta FeOOH) crystals in biofilm samples from the flooded mine. Subsequent work has shown that polymers in other environments, including polymers contained in organized structures, also template iron oxyhydroxide mineralization. Thus, microbial polymer templation of iron oxide minerals appears to be a general phenomenon. We also examined polymer mineralization in culture and abiotic synthesis experiments. We combined alginate, a well-characterized microbial polymer with carboxylic functional groups, and Fe(III) in various forms and reproduced some of the simple structures found in nature. We used STXM (with C, N, O, and Fe NEXAFS) and Fe EXAFS to follow the influence of polymers during mineral formation. NEXAFS data collected to date clearly show an evolution in interactions between polymer functional groups as iron is bound and mineralization proceeds. An understanding of polymer-mediated formation of unique minerals will allow us to better establish these minerals as biosignatures.
DE: 3665 Mineral occurrences and deposits
DE: 1045 Low-temperature geochemistry
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting