Compared to the cell size the external/extracellular electron transfer (EET) can occur over relatively long distances, and its kinetics are controlled by the potential at the electrode (Chong et al. 2021).ĭonating or accepting electrons allows microorganisms to sustain their metabolism, because the electrons flow through the respiratory chains countered by proton flow, which in turn allow e.g., ATP synthesis. 2022) or reduction of CO 2/organics into (larger) organic energy storage molecules and/or biomass, i.e., litho- or electroautotrophic metabolism (Vassilev et al. These living cells, microscopic in size but colossal in terms of their biotechnological potential, are employed for either electricity production from organic compounds, i.e., electrogenesis from organoheterotrophic metabolism transferring electrons from the cell to an electrode (Fricke et al. Graphical Abstractīioelectrochemical systems (BES) or microbial electrochemical technologies utilize microorganisms as biocatalysts (Kracke et al. Secondly, S2-BES and S3-BES showed a preference for acetate as electron donor and c-source, as long as this was available, switching to CO 2 reduction, when acetate was depleted. In conclusion the three triplicates fed with organic and/or inorganic carbon sources demonstrated two forms of diauxie: Firstly, S1-BES showed a preference for the electrode as the electron donor via mediated EET. There was only minor evidence of fully reversible bidirectional EET. S2 and S3 biofilms remained attached to the electrodes. The EAB mixed cultures developed accordingly, with S1 represented by mostly aerobes (84.8%) and being very different in composition to S2 and S3, dominated by anaerobes (96.9 and 96.5%, respectively). More frequent periodic polarization reversal resulted in the increase of maximum oxidative current densities by about 50% for S2-BES and 80% for S3-BES, in comparison to half-batch polarization. Using acetate (S2) as well as a mixture of acetate and carbonate (S3) as the main carbon sources yielded primarily alternating electrogenic organoheterotropic metabolism with the higher maximum oxidation current densities recorded for mixed carbon media, exceeding on average 1 mA cm −2. This yielded biofilm detachment and mediated electroautotrophic EET in combination with carbonate, i.e., dissolved CO 2, as the sole carbon source, whereby the emerged mixed culture (S1) contained previously unknown EAB. To this end, a periodic potential reversal regime between − 0.5 and 0.2 V vs. This study investigated, if a mixed electroactive bacterial (EAB) culture cultivated heterotrophically at a positive applied potential could be adapted from oxidative to reductive or bidirectional extracellular electron transfer (EET).
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