In situ electrophysiological profiling of Shewanella oneidensis MR-1 in a novel single-chamber microfluidic BES featuring a transparent gas diffusion anode

Oxygen plays a crucial role in the operation of bioelectrochemical systems (BESs). Not all microorganisms and bioprocesses thrive in oxygen-rich environments; however, it is crucial for many in supporting their growth and metabolism. Oxygen also competes with an anode as an electron acceptor in certain systems¹. In conventional BES setups, spatial segregation of planktonic and biofilm forming communities occur when oxygen is supplied via headspace or sparging, complicating the physiological investigations. Moreover, visualizing electroactive biofilms in BES in vivo is challenging, as microbial characterization typically occurs post-experiment.

This study aimed at development of a microfluidic BES offering the unique advantage of real time biofilm growth visualization, even while dynamically switching between oxygen concentration (composition ranging from 0.1% to 21% v/v) and an anode as electron acceptors. This was achieved by a channel-type microfluidic gas diffusion layer, separated from the BES anode by a transparent Polydimethylsiloxane (PDMS) membrane, enabling controlled aeration (or anaerobic) conditions at the BES anode. To verify the accurate gas dosing function of the PDMS membrane and validate the overall infrastructure in the Micro-BES, we investigated the aerobic and anodic metabolism of the model electroactive microorganism Shewanella oneidensis MR-1 in the Micro-BES. An electrochemical, secondary metabolite and mediator analysis was performed. Additionally, a fluorescently labelled ATP reporter² strain of S. oneidensis was used to record different growth phases of the electroactive biofilm.

The successful construction of a 0.3 ml BES was presented, allowing for online imaging under diverse operational conditions, including variations in oxygen concentration, working electrode potentials, electrode configurations and mediator concentrations. This comprehensive approach facilitated a thorough functional validation of the system and gave new options for physiological insight into the model electroactive bacterium S. oneidensis.

Lu, M., et al. (2017). Biotechnology and bioengineering 114(1): 96-105Deng, Y., et al. (2021). BMC biology 19(1): 101