Mechanisms of magnetic sensing and regulating extracellular electron transfer of electroactive bacteria under magnetic fields

First and Second Reductions in an Aprotic Solvent: Comparing Computational and Experimental One-Electron Reduction Potentials for 345 Quinones

Using reference reduction potentials of quinones recently measured relative to the saturated calomel electrode (SCE) in N,N-dimethylformamide (DMF), we benchmark absolute one-electron reduction potentials computed for 345 Q/Q•- and 265 Q•-/Q2- half-reactions using adiabatic electron affinities computed with density functional theory and solvation energies computed with four continuum solvation models: IEF-PCM, C-PCM, COSMO, and SM12. Regression analyses indicate a strong linear correlation between experimental and absolute computed Q/Q•- reduction potentials with Pearson's correlation coefficient (r) between 0.95 and 0.96 and the mean absolute error (MAE) relative to the linear fit between 83.29 and 89.51 mV for different solvation methods when the slope of the regression is constrained to 1. The same analysis for Q•-/Q2- gave a linear regression with r between 0.74 and 0.90 and MAE between 95.87 and 144.53 mV, respectively. The y-intercept values obtained from the linear regressions are in good agreement with the range of absolute reduction potentials reported in the literature for the SCE but reveal several sources of systematic error. The y-intercepts from Q•-/Q2- calculations are lower than those from Q/Q•- by around 320-410 mV for IEF-PCM, C-PCM, and SM12 compared to 210 mV for COSMO. Systematic errors also arise between molecules having different ring sizes (benzoquinones, naphthoquinones, and anthraquinones) and different substituents (titratable vs nontitratable). SCF convergence issues were found to be a source of random error that was slightly reduced by directly optimizing the solute structure in the continuum solvent reaction field. While SM12 MAEs were lower than those of the other solvation models for Q/Q•-, SM12 had larger MAEs for Q•-/Q2- pointing to a larger error when describing multiply charged anions in DMF. Altogether, the results highlight the advantages of, and further need for, testing computational methods using a large experimental data set that is not skewed (e.g., having more titratable than nontitratable substituents on different parent groups or vice versa) to help further distinguish between sources of random and systematic errors in the calculations.

Dynamic membrane filtration accelerates electroactive biofilms in bioelectrochemical systems

Bioelectrochemical systems (BES) have emerged as a dual-function technology for treating wastewater and recovering energy. A vital element of BES is the rapid formation and maintenance of electroactive biofilms (EABs). Previous attempts to accelerate EAB formation and improve electroactivities focused on enhancing the bacterial adhesion process while neglecting the rate-limiting step of the bacterial transport process. Here, we introduce membrane filtration into BES, establishing a dynamic membrane filtration system that enhances overall performance. We observed that optimal membrane flux considerably reduced the startup time for EAB formation. Specifically, EABs established under a 25 L m-2 h-1 flux (EAB25 LMH) had a formation time of 43.8 ± 1.3 h, notably faster than the 51.4 ± 1.6 h in the static state (EAB0 LMH). Additionally, EAB25 LMH exhibited a significant increase in maximum current density, approximately 2.2 times higher than EAB0 LMH. Pearson correlation analysis indicated a positive relationship between current densities and biomass quantities and an inverse correlation with startup time. Microbial analysis revealed two critical findings: (i) variations in maximum current densities across different filtration conditions were associated with redox-active substances and biomass accumulation, and (ii) the incorporation of a filtration process in EAB formation enhanced the proportion of viable cells and encouraged a more diverse range of electroactive bacteria. Moreover, the novel electroactive membrane demonstrated sustained current production and effective solid-liquid separation during prolonged operation, indicating its potential as a viable alternative in membrane-based systems. This approach not only provides a new operational model for BES but also holds promise for expanding its application in future wastewater treatment solutions.

Review of cathodic electroactive bacteria: Species, properties, applications and electron transfer mechanisms

Cathodic electroactive bacteria (C-EAB) which are capable of accepting electrons from solid electrodes provide fresh avenues for pollutant removal, biosensor design, and electrosynthesis. This review systematically summarized the burgeoning applications of the C-EAB over the past decade, including 1) removal of nitrate, aromatic derivatives, and metal ions; 2) biosensing based on biocathode; 3) electrosynthesis of CH4, H2, organic carbon, NH3, and protein. In addition, the mechanisms of electron transfer by the C-EAB are also classified and summarized. Extracellular electron transfer and interspecies electron transfer have been introduced, and the electron transport mechanism of typical C-EAB, such as Shewanella oneidensis MR-1, has been combed in detail. By bringing to light this cutting-edge area of the C-EAB, this review aims to stimulate more interest and research on not only exploring great potential applications of these electron-accepting bacteria, but also developing steady and scalable processes harnessing biocathodes.