Whole cell electrochemistry of electricity-producing microorganisms evidences an adaptation for optimal exo-cellular electron transport

BUSALMEN, JUAN PABLO; ESTEVE NUÑEZ, ABRAHAM; MIGUEL FELIU, JUAN

ENVIRONMENTAL SCIENCE & TECHNOLOGY

American Chemical Society

Año: 2008 vol. 42 p. 2445 - 2450

0013-936X

The mechanism(s) by which electricity-producing microorganisms interact with an electrode is poorly understood. Outer membranecytochromes and conductive pili are being consideredas possible players, but the available information does not concur to a consensus mechanism yet. In this work we demonstrate that Geobacter sulfurreducens cells are able to change the way in which they exchange electrons with an electrode as a response to changes in the applied electrode potential. After several hours of polarization at 0.1VAg/AgClsKCl (saturated), the voltammetric signature of the attached cells showed a single redox pair with a formal redox potential of about -0.08 V as calculated from chronopotentiometric analysis. A similar signal was obtained from cells adapted to 0.4 V. However, new redox couples were detected after conditioning at 0.6 V. A large oxidation process beyond 0.5 V transferring a higher current than that obtained at 0.1 V was found to be associated with two reduction waves at 0.23 and 0.50 V. The apparent equilibrium potential of these new processes was estimated to be at about 0.48 V from programmed current potentiometric results. Importantly, when polarization was lowered again to 0.1 V for 18 additional hours, the signals obtained at 0.6 V were found to greatly diminish in amplitude, whereas those previously found at the lower conditioning potential were recovered. Results clearly show the reversibility of cell adaptation to the electrode potential and point to the polarization potential as a key variable to optimize energy production from an electricity producing population.