Electrostatic ethanol fermentation: Experimental study and kinetic-based metabolic modeling

Due to the electrical nature of the cell, it is possible to modulate its behavior through the application of non-lethal external electric fields to improve fermentation processes. In this work, a microbial cell system with a chamber and two electrodes inside and connected to a voltage source was used. One of the electrodes was kept isolated to create an electric field without the flow of current. Cultures with two ethanol-producing microbial strains (<i>Saccharomyces cerevisiae</i> and <i>Zymomonas</i> mobilis) were conducted in this device. The application of voltages between 0 and 18 V was evaluated to determine the impact of the generated electric field on ethanol production. To analyze the possible effect of the field on the central carbon metabolism in each strain, biochemical-based kinetic models were formulated to describe the experimental fermentation kinetics obtained. It was found that low applied voltages did not have significant effects on growth rate in either strain, but all voltages evaluated increased substrate consumption and ethanol production rate in <i>Z</i>. <i>mobilis</i>, while only 18 V affected these rates in <i>S</i>. <i>cerevisiae</i>, indicating that <i>Z</i>. <i>mobilis</i> was the most sensitive to the electric field. At the end of the fermentation, significant increases in ethanol yields of 10.7% and 19.5% were detected for <i>S</i>. <i>cerevisiae</i> and <i>Z</i>. <i>mobilis</i>, respectively. The proposed mathematical models showed that substrate transport through the membrane catalyzed by the phosphotransferase system (PTS) for <i>Z</i>. <i>mobilis</i> and hexose transport proteins mechanism and hexokinase (HK) activity for <i>S</i>. <i>cerevisiae</i> and the transformation of pyruvate to ethanol, catalyzed by the decarboxylase (PDC) and alcohol dehydrogenase (ADH) enzymes, were the reactions most affected by the application of the external field.