Exploring and validating key factors limiting cyanobacteria-based CO2 bioconversion: Case study to maximize myo-inositol biosynthesis

• The highest myo- inositol production from CO 2 was achieved in cyanobacteria. • Balancing the cofactor pools benefit the myo- inositol production. • Artificial sRNAs realizing efficient and simultaneous control of multiple genes. • myo- inositol based biosensor enabled automatic block of competitive pathways. Cyanobacteria have been considered as an ideal photosynthetic chassis for CO 2 recycle and bioconversion, which could make a significant contribution to carbon neutrality. However, several inherited issues associated with current cyanobacterial strains need to be addressed before their biotechnological application, such as slow growth, uneven of carbon distribution, biased production of reducing power and imbalance between growth and biosynthesis. To address the issues, myo -inositol (MI) was selected as an example target and a fast-growing cyanobacterium Synechococcus elongatus UTEX 2973 was utilized as chassis to improve cell growth. Second, several genes involved in MI synthesis were evaluated. Third, the MI biosynthesis was further increased by cofactors enhancement and down regulation of the competing pathways using multiplex artificial small RNAs (PTRNAs). Forth, a MI sensor was developed and optimized to trigger the automatic expression PTRNAs to achieve real-time intelligent regulation, avoiding the growth defect caused by blocking essential genes at early growth stage. Fifth, carbon re-direction was achieved using rhythmical cultivation, resulting in a final production of 262.6 mg/L MI in shaking flask, which represents the highest production from CO 2 in cyanobacteria. Finally, the metabolomic analysis was applied to elucidate the shifted metabolic flux and predicted targets for future optimization. Together of all efforts, we can achieve the CO 2 -based MI biosynthesis to the same order of magnitude as heterogenous microorganisms with suitable scale-up in the future.