Investigating ethanol production using the Zymomonas mobilis crude extract

Abstract

Cell-free systems have become valuable investigating tools for metabolic engineering research due to their easy access to metabolism without the interference of the membrane. Therefore, we applied Zymomonas mobilis cell-free system to investigate whether ethanol production is controlled by the genes of the metabolic pathway or is limited by cofactors. Initially, different glucose concentrations were added to the extract to determine the crude extract's capability to produce ethanol. Then, we investigated the genes of the metabolic pathway to find the limiting step in the ethanol production pathway. Next, to identify the bottleneck gene, a systemic approach was applied based on the integration of gene expression data on a cell-free metabolic model. ZMO1696 was determined as the bottleneck gene and an activator for its enzyme was added to the extract to experimentally assess its effect on ethanol production. Then the effect of NAD+ addition at the high concentration of glucose (1 M) was evaluated, which indicates no improvement in efficiency. Finally, the imbalance ratio of ADP/ATP was found as the controlling factor by measuring ATP levels in the extract. Furthermore, sodium gluconate as a carbon source was utilized to investigate the expansion of substrate consumption by the extract. 100% of the maximum theoretical yield was obtained at 0.01 M of sodium gluconate while it cannot be consumed by Z. mobilis. This research demonstrated the challenges and advantages of using Z. mobilis crude extract for overproduction.

Cutting off the upstream and downstream costs for CO2 electroreduction by upcycling fermentation emissions into ethanol

“…We used 0.1 M glucose solution, as is commonly used in literature, as the fermentation feedstock for yeast to generate ethanol. 34,35 Despite the fact that liquids such as glycerol and organic acids may exist as side products, CO 2 was the only gas product from anaerobic bio-ethanol fermentation, as analyzed by gas chromatography (GC)-that is, almost 100% CO 2 purity (Fig. 2a).…”