Quantification of Electron Transfer Rates to a Solid Phase Electron Acceptor through the Stages of Biofilm Formation from Single Cells to Multicellular Communities

Microbial fuel cell (MFC) technology has enabled new insights into the mechanisms of electron transfer from dissimilatory metal reducing bacteria to a solid phase electron acceptor. Using solid electrodes as electron acceptors enables quantitative real-time measurements of electron transfer rates to these surfaces. We describe here an optically accessible, dual anode, continuous flow MFC that enables real-time microscopic imaging of anode populations as they develop from single attached cells to a mature biofilms. We used this system to characterize how differences in external resistance affect cellular electron transfer rates on a per cell basis and overall biofilm development in Shewanella oneidensis strain MR-1. When a low external resistance (100 Q) was used, estimates of current per cell reached a maximum of 204 fA/cell (1.3 x 10(6) e(-) cell(-1) sec(-1)), while when a higher (1 M Omega) resistance was used, only 75 fA/cell (0.4 x 10(6) e(-) cell(-1) sec(-1)) was produced. The 1 M Omega anode biomass consistently developed into a mature thick biofilm with tower morphology (> 50 mu m thick), whereas only a thin biofilm (<5 mu m thick) was observed on the 100 Q anode. These data suggest a link between the ability of a surface to accept electrons and biofilm structure development.