Lactic Acid from CO2: A Carbon Capture and Utilization Strategy Based on a Biocatalytic Approach.

The EU low-carbon economy aims to reduce the level of CO2 emission in the EU to 80% by 2050. High efforts are required to achieve this goal, where successful CCU (Carbon Capture and Utilization) technologies will have a high impact. Biocatalysts offer a greener alternative to chemical catalysts for the development of CCU strategies since biocatalysis conforms 10 of the 12 principles of green chemistry. In this study, a multienzymatic system, based on alcohol dehydrogenase (ADH), pyruvate decarboxylase (PDC), and lactate dehydrogenase (LDH), that converts CO2 and ethanol into lactic acid leading to a 100% atom economy was studied. The system allows cofactor regeneration, thus reducing the process cost. Through reaction media engineering and enzyme ratio study, the performance of the system was able to produce up to 250 µM of lactic acid under the best conditions using 100% CO2, corresponding to the highest concentration of lactic acid obtained up to date using this multienzymatic approach. For the first time, the feasibility of the system to be applied under a real industrial environment has been tested using synthetic gas mimicking real blast furnace off-gases composition from the iron and steel industry. Under these conditions, the system was also capable of producing lactic acid, reaching 62 µM.

Zymobacter palmae pyruvate decarboxylase production process development: Cloning in Escherichia coli, fed-batch culture and purification.

Pyruvate decarboxylase (PDC) is responsible for the decarboxylation of pyruvate, producing acetaldehyde and carbon dioxide and is of high interest for industrial applications. PDC is a very powerful tool in the enzymatic synthesis of chiral amines by combining it with transaminases when alanine is used as amine donor. However, one of the main drawback that hampers its use in biocatalysis is its production and the downstream processing on scale. In this paper, a production process of PDC from Zymobacter palmae has been developed. The enzyme has been cloned and overexpressed in Escherichia coli. It is presented, for the first time, the evaluation of the production of recombinant PDC in a bench-scale bioreactor, applying a substrate-limiting fed-batch strategy which led to a volumetric productivity and a final PDC specific activity of 6942 U L-1h-1 and 3677 U gDCW-1 (dry cell weight). Finally, PDC was purified in fast protein liquid chromatography equipment by ion exchange chromatography. The developed purification process resulted in 100% purification yield and a purification factor of 3.8.