Engineering ethanologenic bacterium Zymomonas mobilis for economic cellulosic bioethanol production using agro-industrial waste corncob residue

Cellulosic ethanol is an important biofuel derived from lignocellulosic biomass, which has the potential to mitigate environmental pollution and contribute to achieving carbon neutralization for a sustainable circular economy. However, the economic production of cellulosic ethanol is hindered by lack of robust microbial cell factories capable of overcoming the challenges of efficient utilization of C5/C6 sugar mixture and inhibitors in the cellulosic hydrolysate. The ethanologenic bacterium Zymomonas mobilis with excellent industrial characteristics was engineered in this study, which was then applied for bioethanol production at different scales of 5 L, 50 L, and 30 m³ fermentors using the hydrolysate of the agro-industrial waste of corncob residues. The results demonstrated that the recombinant Z. mobilis had a consistent fermentation performance from lab-scale flasks to pilot-scale fermentors up to 30 m³ with the ethanol titer, yield, and productivity above 60 gꞏL⁻¹, 0.47 gꞏg⁻¹, and 3.0 gꞏL⁻¹ꞏh⁻¹, respectively. Techno-economic analysis (TEA) and life cycle assessment (LCA) were performed to evaluate the commercialization potential and environmental impacts of this process. The TEA indicated that the minimum selling price of ethanol with an annual capacity of 16,000 tons ranged from $0.58 kg⁻¹ to $0.79 kg⁻¹ with a 10 % internal rate of return. The LCA suggested that this process could reduce greenhouse gas emissions by 57 % compared to fossil fuels. The consistent performance of recombinant strain of Z. mobilis at different scales and the economic feasibility for cellulosic bioethanol production highlight the potential of Z. mobilis as a suitable cell factory for commercial biomanufacturing of lignocellulosic biochemicals using sustainable agro-industrial feedstocks.