Cell appendix formation is a common phenomenon throughout a variety of bacterial species for cell-cell interaction, cell adhesion as well as for cell movement. Moreover, in bioelectrochemical systems (BES) cell appendages have been shown to participate in electron transfer between the cells and the electrode surface. In this work, the cell appendix formation of Clostridium acetobutylicum in biofilms on the working (WE) and counter electrodes (CE) of a bioelectrochemical systems (BES) are imaged and compared to biofilms of a conventional fermentation using scanning elect ron microscopy. It is found that under all observed conditions the cells possess filamentous appendages with a higher number and a denser network observed in the BES. Additionally, when using conductive atomic force microscopy, a current response of about 15 nA was found for the cell appendages of C. acetobutylicum after cultivation in a BES. This study is the first report of a conductivity of cell appendices of Clostridia and represents therefore the basis for further studies on the role of appendices for biofilm formation and electron transfer of Clostridia in BESs.

ChemElectroChem; accepted paper http://dx.doi.org/10.1002/celc.201901656