CALCITE SURFACE RECOGNITION BY SHEWANELLA ONEIDENSIS MR-1: INSIGHT INTO CARBONATE DISSOLUTION RATES IN BIOLOGICAL ENVIRONMENTS

Determining and quantifying the factors that control calcite dissolution rates in natural environments are central to understanding carbon sequestration and many biogeochemical cycles. While most laboratory work has focused on measuring calcite dissolution rates under abiotic conditions, it is likely that natural calcite weathering rates are significantly influenced by biological activity. Unfortunately, direct quantification of microbially-mediated dissolution rates are often complicated by an inability to discern relative contributions from direct microbe-mineral surface interactions (biofilm formation) and changes in the solution environment resulting from biological activity. Such determinations require a noninvasive imaging technique that can both detect the microbe at the mineral surface and quantify any resulting changes in surface topography. Vertical scanning interferometry (VSI) meets these requirements and enables the measurement of both local dissolution (etch pits) and global dissolution rates (surface normal retreat). We have previously demonstrated that Shewanella oneidensis MR-1 is capable of altering calcite dissolution rates by detecting and attaching to sites on the mineral surface where etch pits are energetically likely to form. Recognition of these high-energy sites occurs rapidly enough so that occlusion, coupled with biofilm formation, prevents the development of any further pitting. This study expands these exciting preliminary results to include the interactions of MR-1 with calcite under more environmentally-relevant conditions. A modified marine environment (seawater) was used to determine the manner by which the nutrient and physical environment influences the ability of MR-1 to recognize and attach to calcite surfaces, thereby demonstrating its role in modifying calcite dissolution rates. These results will provide an understanding of calcite dissolution rates that is relevant to many biological environments.