CONICET | Buscador de Institutos y Recursos Humanos

Exocellular electron conduction is one of the most fascinating discoveries of microbiology in the last decade. In natural and man-made environments it is thought to play a fundamental role, allowing the exchange of electrons between bacterial cells and between these and external electronic acceptors. Moreover, it is one of the fundamental processes behind the production of electricity by electroactive biofilms grown on electrodes, which are of paramount importance in emerging technologies as microbial fuel cells, microbial electrolysis cells, the microbial electrosynthesis process, and whole cell biosensors. Aiming at gaining information on structural and physiological features of electricity-producing biofilms, we have constructed an electrochemical cell that can be mounted on the stage of a microscope. The cell is designed to use thin film transparent electrodes, thus allowing the observation of biofilms in situ and in vivo through the electrode. By this cell in conjunction with a confocal Raman microscope (CRM), the redox state of molecules at different focal planes of Geobacter sulfurreducens biofilms was explored. Obtained results showed a redox gradient across electricity-producing biofilms which was dependent on the potential applied to the electron acceptor, with the fraction of reduced species being higher in upper layers of the biofilm. Therefore, respiration in these layers is expected to be limited. The approach provided new information about internal biofilm physiology, relevant for the understanding energy production constrains and electron conduction mechanisms in these systems.