Increasing the atom economy of glucose fermentation for bioethanol production in Rubisco-based engineered Escherichia coli

Abstract

Feedstock accounts for a major portion of bio-based chemical production. While tremendous progress has been made in cellulosic ethanol production over the last few decades, direct conversion of CO2 to biofuels has been under-investigated. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is an enzyme that can fix CO2 by catalyzing the carboxylation. A Rubisco-based Escherichia coli has been constructed that is capable of simultaneously converting glucose and CO2 to bioethanol. Practically homo-fermentative ethanol production can be achieved by FB295A (E. coli BL21(DE3) Δzwf ΔldhA Δfrd ΔpflB harboring pdc, adhB, rbcLS, and prk) in 60 h where the bioethanol yield, concentration, percentage/fermentation product, and CO2 emission/ethanol production were 2.3 ± 0.2 mol/molglucose, 256 ± 19 mM, 100 %, and 0.13 ± 0.02 molCO2/molEtOH, respectively. By a subculture to the second generation, the overall fermentation time was shortened within 30 h and therefore, the bioethanol productivity was improved to 7.1 ± 0.5 mmol⋅L−1⋅h−1 while maintaining an apparent ethanol yield of 2.4 ± 0.1 mol/molglucose. The performance of FB295A reached 100 % theoretical for in situ CO2 recycling. This study presents a new bioethanol production pathway based on in situ CO2 recycling.