Finding the comfort zone: Online-monitoring of electroactive bacteria colonising electrode surfaces with different chemical properties

Mechanisms of electron transfer vary greatly within the diverse group of electroactive microorganisms and so does the need to attach to the electrode surface, e.g. by forming a biofilm.

Electrochemical impedance spectroscopy (EIS) and confocal laser scanning microscopy (CLSM) are well established methods to monitor cell attachment to an electrode surface and have therefore been combined in a flow cell as a screening system. The flow cell, equipped with a transparent indium tin oxide working electrode (ITO WE), allows monitoring of attachment processes in real time with minimal needs for additional biofilm preparation. In preliminary experiments the flow cell was successfully used as microbial fuel cell (MFC) with a potential of +0.4 V vs. Ag/AgCl using Shewanella oneidensis as electroactive model organism. [1]

Commonly, graphite-based electrode materials are used in bioelectrochemical systems due to their low costs and high conductivity. However, the hydrophobic and negatively charged surface is not yet optimal for microbial attachment. There are numerous attempts on electrode surface engineering in order to overcome this problem. In the majority of studies the biofilm analysis and evaluation of the attachment takes place at the end of the experiment, neglecting the impacts of the chemical surface properties and initial electrode conditioning during the very beginning of biofilm formation.

To investigate initial attachment and biofilm formation in real-time, the transparent ITO-electrode is coated with polyelectrolytes differing in hydrophobicity and polarity to evaluate their effects on the initial surface colonisation by different electroactive microorganisms. Combining CLSM and EIS, both, surface coverage and electrochemical interaction of electrode-associated bacteria can be assessed.

With this we aim to understand and ease initial steps of biofilm formation to improve efficiency of bioelectrochemical applications, e.g. with regards to start-up time.

 

[1] Stöckl, M., Schlegel, C., Sydow, A., Holtmann, D., Ulber, R., & Mangold, K. M. (2016). Membrane separated flow cell for parallelized electrochemical impedance spectroscopy and confocal laser scanning microscopy to characterize electro-active microorganisms. Electrochimica Acta, 220, 444-452.