## 3 Results and Discussion  
### C. pasteurianu Electroactivity in MFCDSM  
Figures 1A and 1B, respectively, show the power/polarization and EIS curves recorded for _C. pasteurianum_ DSM 525 operating in an MFC with 1 g.L\({}^{-1}\) glycerol added (MFCDSM).  
The maximum power achieved with MFCDSM and the abiotic control was 0.39 and 0.22 \(\upmu\)W\(\cdot\)cm\({}^{-2}\), respectively. The maximum current density achieved with MFCDSM and the abiotic control was 3.02 and 1.72 \(\upmu\)A\(\cdot\)cm\({}^{-2}\), respectively. In other words, the current density almost doubled in the presence of _C. pasteurianum_ DSM 525, indicating that this biocatalyst can perform direct EET to the electrode, effectively transferring electrons through the external circuit.  
Although the genus _Clostridium_ is typically known for its fermentative ability, it has also been demonstrated to transfer electrons to electrodes through ferredoxin-mediated processes [18]. However, the electroactive activity of _C. pasteurianum_ remains considerably limited and poorly understood. Only in 2014 did [PERSON] et al. suggest that _C. pasteurianum_ is electroactive. These authors showed that _C. pasteurianum_ DSM 525 can use both the electrode and substrate (glycerol and glucose) as electron donors through DET in a BES. By employing CV, the authors observed well-defined but asymmetric redox peaks for _C. pasteurianum_ DSM 525, which indicates a quasi-reversible reaction. The authors highlighted similarities between these asymmetric peaks and the peaks observed for other electroactive microorganisms that can reduce Fe (III) and produce current [8].  
Furthermore, the polarization curves obtained for \(\mathrm{MFC_{DSM}}\) and the abiotic control showed an about 1.7-fold lower MFC internal resistance in the former case (9933 and 17,022 \(\Omega\), respectively). Polarization curves are a valuable tool to understand how an MFC behaves because they allow the main domains of potential losses limiting performance to be identified [19; 20].  
Also, we used EIS to describe how \(\mathrm{MFC_{DSM}}\) and the abiotic control behave. We conducted the EIS tests at OCP (\(\mathrm{MFC_{DSM}}=-0.265\) V; abiotic control = \(-0.331\) V vs. Ag/AgCl(\(\mathrm{Sat}\)). From these values, we generated a Nyquist plot (Figure 1B), which provided information about the resistance of the solution (R\({}_{\mathrm{g}}\)), namely 96.30 and 16.10 \(\Omega\) for \(\mathrm{MFC_{DSM}}\) and the abiotic control, respectively. We attributed the higher Rs obtained for \(\mathrm{MFC_{DSM}}\) to the presence of microorganisms in the solution [21].  
Additionally, total impedance (R\({}_{\mathrm{ct}}\)), which is associated with the charge transfer process, was 17-fold lower for \(\mathrm{MFC_{DSM}}\) compared to the abiotic control (65 and 1128 \(\Omega\), respectively). This indicated that _C. pasteurianum_ DSM 525 enhanced the efficiency of the overall electron transfer process. At low frequencies, a straight line characteristic of limited diffusion processes arose [21]. Moreover, the double layer capacitance (C\({}_{\mathrm{dl}}\)) of \(\mathrm{MFC_{DSM}}\) was 2.2-fold higher (C\({}_{\mathrm{dl}}\) = 3.8 \(\upmu\)F\(\cdot\)cm\({}^{-2}\)) compared to the abiotic control (C\({}_{\mathrm{dl}}\) = 1.7 \(\upmu\)F\(\cdot\)cm\({}^{-2}\)). The _C. pasteurianum_ DSM 525 present on the electrode probably helped to increase C\({}_{\mathrm{dl}}\).