Abstract
BackgroundAcetoin, especially the optically pure (3S)- or (3R)-enantiomer, is a high-value-added bio-based platform chemical and important potential pharmaceutical intermediate. Over the past decades, intense efforts have been devoted to the production of acetoin through green biotechniques. However, efficient and economical methods for the production of optically pure acetoin enantiomers are rarely reported. Previously, we systematically engineered the GRAS microorganism Corynebacterium glutamicum to efficiently produce (3R)-acetoin from glucose. Nevertheless, its yield and average productivity were still unsatisfactory for industrial bioprocesses.ResultsIn this study, cellular carbon fluxes in the acetoin producer CGR6 were further redirected toward acetoin synthesis using several metabolic engineering strategies, including blocking anaplerotic pathways, attenuating key genes of the TCA cycle and integrating additional copies of the alsSD operon into the genome. Among them, the combination of attenuation of citrate synthase and inactivation of phosphoenolpyruvate carboxylase showed a significant synergistic effect on acetoin production. Finally, the optimal engineered strain CGS11 produced a titer of 102.45 g/L acetoin with a yield of 0.419 g/g glucose at a rate of 1.86 g/L/h in a 5 L fermenter. The optical purity of the resulting (3R)-acetoin surpassed 95%.ConclusionTo the best of our knowledge, this is the highest titer of highly enantiomerically enriched (3R)-acetoin, together with a competitive product yield and productivity, achieved in a simple, green processes without expensive additives or substrates. This process therefore opens the possibility to achieve easy, efficient, economical and environmentally-friendly production of (3R)-acetoin via microbial fermentation in the near future.
Highlights
Acetoin, especially the optically pure (3S)- or (3R)-enantiomer, is a high-value-added bio-based platform chemical and important potential pharmaceutical intermediate
The commercial production of acetoin is mostly based on chemical methods with many disadvantages, such as high cost, high pollution, and low yield [5]
Analytical methods The biomass concentration was calculated from O D600 values using an experimentally determined correlation 1 OD600 unit is equal to 0.25 g/L cell dry weight (CDW) [29]
Summary
Especially the optically pure (3S)- or (3R)-enantiomer, is a high-value-added bio-based platform chemical and important potential pharmaceutical intermediate. Efficient and economical methods for the production of optically pure acetoin enantiomers are rarely reported. The biotechnological production of safe and natural acetoin could be more ecological and sustainable than their chemical counterparts [8, 9] These methods, including microbial fermentation [8, 10, 11], whole-cell biocatalysis [12, 13] and enzymatic biocatalysis [14, 15], have gained great attention over the past decades. Gluconobacter oxydans NL71 could produce 165.9 g/L acetoin from 2,3-butanediol in a whole-cell catalysis process [17]. By constructing an efficient E. coli whole-cell biocatalyst, Guo et al [19] obtained a high (3R)-acetoin titer of 86.7 g/L from optically pure (R,R)-2,3-butanediol. The expensive chiral substrate, and the complicated, costly processing steps, such as protein purification through Ni–NTA affinity chromatography or centrifugation to concentrate the catalyst cells, made it economically unfeasible in industrial applications
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
