Physiological stratification in electricity-producing biofilms of Geobacter sulfurreducens.

The elucidation of mechanisms and limitations in electrode respiration by electroactive biofilms is significant for the development of rapidly emerging clean energy production and wastewater treatment technologies. In Geobacter sulfurreducens biofilms, the controlling steps in current production are thought to be the metabolic activity of cells, but still remain to be determined. By quantifying the DNA, RNA, and protein content during the long-term growth of biofilms on polarized graphite electrodes, we show in this work that current production becomes independent of DNA accumulation immediately after a maximal current is achieved. Indeed, the mean respiratory rate of biofilms rapidly decreases after this point, which indicates the progressive accumulation of cells that do not contribute to current production or contribute to a negligible extent. These results support the occurrence of physiological stratification within biofilms as a consequence of respiratory limitations imposed by limited biofilm conductivity.