Expression Analysis of Geobacter sulfurreducens During Growth on a Flow-through Potentiostat

G. sulfurreducens can generate electricity from the oxidation of organic compounds. This is because it can take electrons from organic compounds and ship them out to the outer surface of the cell where they can then be deposited on various insoluble electron acceptors including electrodes. Cells attatched to the surface of an electrode oxidize acetate and and deposit the electrons derived from acetate onto the surface of the electrode after which they can travel through an electrical circuit, producing a current. Microbial fuel cells powered by acetate oxidation by Geobacter species are called Geobatteries. In this experiment we compared gene expression in a biofilm of the wild type strain growing on the surface of an electrode within a current-producing Geobattery to gene expression in a wild type biofilm that is not producing current, but is growing on the surface of an electrode. In both cases, the cells were growing in a flow-through two chambered H-cell Geobattery setup. This consists of two glass chambers, an anoxic anode chamber containing G. sulfurreducens, a graphite electrode, a reference electrode and growth medium and an oxic chamber containing the counter electrode. The two chambers are connected by a cation selective membrane and a wire connected to a potentionstat. A potentiostat is an instrument which maintains the redox potential of the anode at a fixed value relative to a reference electrode. Media continuously flowed through the anoxic anode chamber at a dilution rate of 0.15. In the experimental condition, the Geobattery was operational. The circuit was closed and G. sulfurreducens attached to the electrode generated current as it oxidized acetate. The redox potential at the anode was poised at 300 mV by the potentiostat. In the control condition, everything was the same, except that the medium in the anode chamber contained fumarate as electron acceptor, and the anode was not hooked up to the potentiostat i.e. the circuit was open. This prevented the anode from serving as an electron acceptor. Nevertheless a thick G. sulfurreducens biofilm grew on the surface of the electrode. The control and experimental geobatteries were harvested when current in the operational/experimental Geobatteries reached 10 mA. Keywords: two condition comparison Three biological replicates were hybridized in duplicate on 12K Combimatrix sense-detecting arrays, the experiment (10 mA potentiostat) was labeled Cy5, and the control (fumarate biofilm) was labeled with Cy3.