Electrochemical communication between electrodes and rhodobacter capsulatus grown in different metabolic modes

The majority of efforts on microbial and photosynthetic microbial fuel cells are both curiosity driven and made to possibly meet the future growing demand for sustainable energy. The most metabolically versatile purple bacteria Rhodobacter capsulatus is a potential candidate for this purpose. However, utilizing bacteria in such systems requires efficient electronic transfer communication between the microbial cells and the electrodes, which is one of the greatest challenges. Previous studies demonstrated that osmium redox polymers (ORPs) could be used for extracellular electron transfer between the cells and electrodes. Recently, heterotrophically grown R. capsulatus has been wired with ORP modified electrodes. Here in this communication, we report electron transfer from R. capsulatus grown under heterotrophic as well as under photoheterotrophic conditions to electrodes. The cells, immobilized on bare graphite and ORP modified graphite electrodes, were excited with visible light and subsequent photosynthetic electron transfer was recorded using cyclic voltammetric and chronoamperometric measurements. Photoheterotrophically grown R. capsulatus cells on bare graphite generate a significant photocurrent density of 3.46μAcm^-2, whereas on an ORP modified electrode the current density increases to 8.46μAcm^-2. Furthermore, when 1mM p-benzoquinone is added to the electrolyte the photocurrent density reaches 12.25μAcm^-2. Our results could have significant implications in photosynthetic energy conversion and in development of photobioelectrochemical devices.