Electrogenic bacteria (EB) are able to displace respiratory electrons to solid phase terminal electron acceptors. These can be an electrode in a bioelectrochemical system where the electrons are captured as current or, in natural environments, metal oxides. Electrogenic bacteria have been studied as means to generate renewable energy and they are thought to mediate corrosion processes occurring at deep-sea applications. Despite many EB being of marine origin, little is known about their electrogenic mechanisms under high pressure. Particularly, it remains unclear how high hydrostatic pressure affects the respiration process via extracellular electron transfer (EET) in electrogenic bacteria. Shewanella oneidensis is a model electrogenic organism whose genome has revealed redundant respiration pathways that are inactive at atmospheric pressure. We designed a novel high-pressure bioelectrochemical reactor to test the electroactivity change of S. oneidensis in real time (n =3) at pressures of 0.1, 10, 20, and 30 MPa, the latter equivalent to a depth of 3,000 m under the sea level. Chronoaperometry was used to track the current for 2.5 days. A volume of 300 uL of bacterial culture was enclosed with the working electrode in a semipermeable membrane bag placed into a 50 mL inner compressible reactor filled with M1 modified medium. We observed a positive, statistically significant, correlation between pressure and current production (Fig. 1). The higher the pressure, the higher the current harvested, which suggests that EET processes are enhanced by increased pressure. Metatranscriptomic analysis of bacterial RNA is currently ongoing, which would allow identification of relevant microbial respiration genes transcribed at different pressures. Understanding the respiration pathway of electrogenic bacteria under high pressure can enable strategies to prevent biocorrosion, with implications for deep-sea applications. The custom-made bioreactor system employed in this study can be used for further research into high-pressure EET bacterial mechanisms.
