Final Activity Report Summary - INTERBAC (Interfacial Electrochemical Bacterial Recognition) The INTERBAC project studied the fundamental physical chemistry of cell-substrate interactions between electrodes and bacteria, with particular emphasis on the electrochemical ones. It aimed to understand the role of applied currents or voltages in bacterial adhesion and growth, as well as in the production of electric current from bacteria. The main outputs of the incoming phase, originating from the use of electrochemical techniques, such as cyclic voltammetry, chronopotentiometry and chronocoulometry, in combination with spectroscopic infrared adsorption techniques, allowed for the study of electrochemical processes of both aerobic and anaerobic whole live cells and the determination of the cell surface interaction at the molecular level. The obtained principal results indicated that interfacial water was displaced during bacterial adhesion enabling the direct contact between molecules in the bacterial outermost layer and the electrode surface. Cell surface proteins played a major role in this contact, determining bacterial adhesion. Adhesion was found to be dependent on the electrode electrochemical potential, increasing as the positive charge of the surface increased. When working with aerobic bacteria such as p. fluorescens, a transient current was obtained upon positive polarisation. When related to the amount of cells adhered to the electrode, the current was determined to occur because of the oxidation of cell surface proteins and lipopolysaccharides. The oxidation of these molecules was proposed to interfere with growth of individual cells and biofilms. Through working with anaerobic bacteria such as g. sulfurreducens the production of current from cells attached to the electrode was studied. It was found to be mediated by the oxidation of external redox molecules participating in cell's respiration, thus allowing for a direct connection of electrodes to the cell's metabolism. Participating molecules were found to be distinct, depending on the polarisation potential. The formal potential of the various cell redox processes was determined, providing very important information for the implementation of Microbial fuel cells (MFCs). In the next step, molecules involved in the direct electron transport to electrodes were found to be c-type cytochromes. The results showed that charge was transferred upon the conformational redox transition of cytochromes, which constituted the elucidation of the intimate molecular mechanism of current production from electrogenic bacteria. Active work continued during the return phase through the collaboration with European Institutions, such as the University of Alicante, Centre for Astrobiology (CAB), in Madrid. Within other research works described below, the spectroelectrochemical work was extended to prove that a redox couple at higher potential in g. sulfurreducens was also a c-type cytochrome. Indeed, a first insight was gained into the structure of the respiratory chain of attached cells through a voltammetric analysis. In addition, using voltammetry on single crystal electrodes, a possible structure sensitive bacterial response was detected that was under study by the time of the project completion. Based on the strong support received from the European Community and the valuable collaboration with European laboratories, a new line of research in bioelectrochemistry of microorganisms started at the Argentinean Institution. New students at both graduate and under graduate levels were incorporated and specific funds were requested. The group would explore the fundamentals of the electrochemical interaction between bacterial cells and electrodes, aiming to develop relevant applications such as, among others, microbial fuel cells, biosensors, microbial bioremediation processes and microbial corrosion. The initiative appealed great interest to the local scientific community and the public, as demonstrated by the presentations in invited conferences, the publication of invited papers and the diffusion through the press. The platform for this enterprise was a 70 m2 laboratory provided by the 'Instituto de Investigaciones en Ciencia y Tecnologia de Materiales' (INTEMA). Financial support to warrant the continuity of the work was requested to the European Community via the Seventh Framework Programme. The proposal was identified as 'Bacwire' (229337) and included the participation of researchers from the University of Liverpool in the United Kingdom, the University of Bern in Switzerland, the University of Alicante and the University of Alcalá de Henares in Spain, the University of Mar del Plata in Argentina and a Small and medium-sized enterprise (SME), Electrocell from Denmark. The consortium had been called into negotiation by the completion of the INTERBAC project reporting period.
