Mediated electrocatalysis at a biocatalyst electrode based on a bacterium, Gluconobacter industrius

Abstract

Mediated amperometr ic enzyme electrodes use oxidoreductases as catalysts to oxidize or reduce the substrates bioelectrocatalytically in the presence of redox molecules serving as mediators [1-3]. We are interested in the use of microorganisms in place of enzymes. It was reported in early 1966 [4] that Fe(CN)63acted as an electron acceptor for the metabolic oxidation of o-glucose by Escherichia coli (E. coli). This means that in principle, Fe(CN) 3can be used as a mediator to couple the oxidation reaction of o-glucose by E. coli to the electrode reaction of Fe(CN)63-. At tempts to use mediators to shuttle electrons from a bacterial respiratory chain to an electrode were made in biofuel cell configurations [5,6]. In a few whole cell-based biosensors, mediators have been employed to divert electrons from the micro-organisms to the electrode for monitoring photosynthetic activity [7] or eubacterial respiration [8]. However, the details of the electrocatalytic reaction have not been investigated, and the redox compounds taking part in the catalytic reaction are not clear. There is no report on studies of whole cell-based electrodes from a bioelectrocatalysis point of view. A number of micro-organisms have oxidoreductases in their cytoplasmic membranes. The oxidoreductase reaction may be linked to an electrode reaction by the use of an appropriate mediator as illustrated schematically in Fig. 1. We have tested several kinds of bacteria as catalysts and observed small currents resulting