Shewanella oneidensis is an electroactive bacterium that has the ability to harvest electrons from insoluble metals in its environment for biological processes via dissimilatory metal reduction (DMR). There are 4 mechanisms by which S. oneidensis accomplishes these reductions: direct contact of the outer cell membrane to the metals, protein “nanowires” that extend from the cell surface, metal chelators that solubilize the metals, and small molecule electron shuttles. While evidence suggests S. oneidensis predominately utilizes soluble electron shuttles for DMR, it has yet to be directly proven. If the exact mechanism or mechanisms could be elucidated, S. oneidensis could be employed in a fuel cell that rids polluted water of metal contaminants in the process of generating electricity.

For this research, scanning electrochemical microscopy (SECM) was used to investigate the DMR processes of S. oneidensis. By coupling SECM to an inverted microscope, we optically imaged the bacteria during two-dimensional electrochemical measurements. Combined with advances in carbon ultra-micro electrode fabrication, this optical-SECM was used for high resolution scans of S. oneidensis biofilms, as well as planktonic bacteria.