Clostridium Acetobutylicum’s Connecting World: Cell Appendage Formation in Bioelectrochemical Systems

Bacterial cell appendix formation supports cell‐cell interaction, cell adhesion and cell movement. Additionally, in bioelectrochemical systems (BES), cell appendages have been shown to participate in extracellular electron transfer. In this work, the cell appendix formation of Clostridium acetobutylicum in biofilms of a BES are imaged and compared with conventional biofilms. Under all observed conditions, the cells possess filamentous appendages with a higher number and density in the BES. Differences in the amount of extracellular polymeric substance in the biofilms of the electrodes lead to the conclusion that the cathode can be used as electron donor and the anode as electron acceptor by C. acetobutylicum. When using conductive atomic force microscopy, a current response of about 15 nA is found for the cell appendages from the BES. This is the first report of conductivity for clostridial cell appendices and represents the basis for further studies on their role for biofilm formation and electron transfer. Out of the cell: This study illustrates that Clostridium acetobutylicum forms cell appendages under all studied conditions with a denser network in biofilms of bioelectrochemical systems compared to conventional cultivations. A current response of about 15 nA of the cell appendices is measured with conductive atomic force microscopy. Moreover, an increased extracellular polymeric substance (EPS) formation in the biofilm of the cathode is observed compared to the anode, which encourages further studies about the electron transfer between C. acetobutylicum and electrodes acting as electron acceptors and donors.