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The effect of CO2 in enhancing photosynthetic cofactor recycling for alcohol dehydrogenase mediated chiral synthesis in cyanobacteria

Sengupta, Annesha, Sunder, Avinash Vellore, Sohoni, Sujata V., Wangikar, Pramod P.
Journal of biotechnology 2019 v.289 pp. 1-6
Lactobacillus kefiri, NADP (coenzyme), Synechococcus sp. PCC 7942, acetophenones, alcohol dehydrogenase, biocatalysts, biotransformation, carbon dioxide, carbon dioxide enrichment, glucose, nicotinamide, photosynthesis, stereoselective synthesis
The light harvesting photosystem in cyanobacteria offers a potential pathway for the regeneration of the nicotinamide cofactor NADPH, thereby facilitating the application of cyanobacteria as excellent whole cell biocatalysts in oxidoreductase-mediated biotransformation. The use of cyanobacterial metabolism for cofactor recycling improves the atom economy of the process compared to the commonly employed enzyme-coupled cofactor recycling using enzymes such as glucose dehydrogenase. Here we report the asymmetric conversion of acetophenone to chiral 1-phenylethanol by recombinant Synechococcus elongatus PCC 7942 whole cell biocatalyst that expresses the NADPH dependent L. kefir alcohol dehydrogenase. Besides light, it was observed that carbon dioxide levels play a critical role in improving the bioconversion efficiency possibly due to the enhanced growth rate and improved cofactor availability at elevated CO2 levels. Complete reduction of acetophenone to optically pure (R)-1-phenylethanol at 99% enantiomeric excess was achieved within 6 h with a relatively low cell density of 0.66 g/l by coupling optimum light and CO2 levels and without the need for a co-substrate.