Expression Analysis of Geobacter sulfurreducens Current-Consuming Biofilm versus Current-Producing Biofilm

There is a wide diversity of potential applications for direct electron transfer from electrodes to microorganisms, which might be better optimized if the mechanisms for this novel electrode-biofilm interaction were better understood. Geobacter sulfurreducens is one of the few microorganisms available in pure culture that is known to be capable of directly accepting electrons from a negatively poised electrode. A microarray comparison of cells accepting electrons from the electrode versus cells donating electrons to the electrode reveals that the genes previously observed to be upregulated in current-producing biofilms are not highly expressed in current-consuming biofilms. Current-consuming biofilms were grown under anoxic conditions in freshwater medium in a potentiostat-poised (-500 mV vs. Ag/AgCl), dual-chambered electrode system where the electrode served as the electron donor and fumarate as the electron acceptor. Current-producing biofilms were grown under identical condition, except the electrode served as the electron acceptor (+300 mV vs. Ag/AgCl) and acetate as the electron donor. Triplicate electrode systems of either current-consuming biofilms or current-producing biofilms were harvested for total RNA.