MICROBIAL RECOGNITION OF MAGNESITE AND DOLOMITE SURFACES: IMPLICATIONS FOR CARBONATE DISSOLUTION RATES

One of the major challenges of biogeochemistry is to resolve the precise manner by which microbial activity influences mineral-surface reactions. While a prerequisite for biological activity at a surface is substrate recognition and attachment, probing the nature of this biological-geological interface is inherently difficult. A noninvasive imaging technique is needed that can detect the microbe at the surface and quantify any resulting changes in mineral-surface topography, while maintaining both a high spatial resolution and a large field of view. Vertical scanning interferometry (VSI) meets these requirements and enables the measurement of both local dissolution (etch pits) and global dissolution rates (surface normal retreat). Recent VSI work by our group has focused on the effects of the surface-active microbe Shewanella oneidensis MR-1 on the dissolution of calcite. While previous investigators have focused on the interactions of MR-1 with metal oxide surfaces, many important geological processes, such as those governing the global carbon cycle, are principally influenced by carbonate and silicate weathering (dissolution). Our previous findings have indicated that MR-1 is capable of altering calcite and dolomite 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 extends our understanding of the effects of MR-1 on carbonate dissolution rates by 1) studying the interactions of MR-1 with magnesite and 2) determining the interactions of MR-1 with dolomite and magnesite under more environmentally-relevant conditions (seawater) than previous experiments. These results will provide greater insight into the chemical and physical factors that control microbial recognition and modification of geological surfaces.