Insights from voltammetry of electrode-reducing bacteria under nonturnover conditions

Voltammetry in the presence and absence of substrates shows that bacteria such as Geobacter sulfurreducens and Shewanella oneidensis appear have natural mechanisms that solve many key issues common to enzymatic fuel cells. For example, by analyzing films containing only the first cells to colonize surfaces (sub-monlayers), it appears that Geobacter quickly brings key redox proteins in contact with electrodes, allowing cellular oxidative machinery to operate near its maximum rate, while Shewanella still demonstrates a bottleneck at the cell-electrode interface, requiring mediators to facilitate rapid electron transfer. As cells stack on top of one another, akin to loading enzymes in a matrix, these species also demonstrate significant differences in terms of their ability to relay electrons between cells, and to the cell-electrode interface. Voltammetry in the absence of substrates has provided new insights into the nature of electron transfer within these films as they transition from sub-monolayer to multicellular thickness.