Nanoparticle Mediated NADPH Regeneration for Enhanced Ethanol Production by Engineered Synechocystis sp. PCC 6803

ABSTRACT The ethanol synthesis pathway engineered Synechocystis sp. PCC 6803 was used to investigate the influence of metal oxide mediated NADPH regeneration on ethanol synthesis. Among the metal oxides, Fe 2 O 3 and MgO showed considerable improvement in growth, chlorophyll a content and ethanol synthesis. The in-vitro studies proved that the selected metal oxides have the potential to regenerate the NADPH under light illumination. The results clearly indicate that the light energy is the key factor for activation of metal oxides and to a less extent light itself has the possibility for direct regeneration of NADPH. Under optimized light intensity and NADP addition, the maximum MgO mediated ethanol production of 5100mg/L, about a 2-fold increase compared to the control, was obtained after 20 days cultivation at 5L level. This study indicates that the efficient NADPH regeneration aided by metal oxide is crucial to improve ethanol productivity in Synechocystis sp. PCC 6803. IMPORTANCE Cyanobacteria are efficient ethanol producing organisms from atmospheric CO 2 upon engineering of pathway. In cyanobacterial ethanol synthesis pathway, NADPH plays an important role acetaldehyde to ethanol conversion. Here we elucidated the NADPH regeneration through extracellular addition of metal oxides. The metal oxide mediated NADPH regeneration study allows us to dissect the importance of metal oxides in enhancing ethanol production through NADPH regeneration while also providing insight into the regulatory functions of metal oxides in growth, photosynthetic apparatus and various carbon metabolisms.