Metabolic engineering of fast growing cyanobacteria for phototrophic production of 2,3-butanediol

Metabolic engineering of cyanobacteria holds great potential for sustainable photosynthetic production of platform chemicals from CO₂. However, product titers have been significantly low due to the slow growth rates of available model strains and lack of adequate synthetic biology tools. Here, we engineered three newly isolated fast growing Synechococcus elongatus strains PCC 11801, PCC 11802, and IITB6 for production of the platform chemical 2,3-butanediol. Importantly, we used native cyanobacterial promoters to enable inducer-free gene expression and 2,3-butanediol production. Different combinations of these native promoters were employed to optimize expression of the three-gene 2,3-butanediol synthesis pathway. Among the strains tested in this study, the highest 2,3-butanediol titer of 1.62 g L⁻¹ (130 mg L⁻¹ Day⁻¹) was obtained in IITB6 (P_cpcB300:alsS::P_psbAIII:alsD::P_rbcL:adh), with the highest reported photosynthetic productivity in cyanobacteria cultivated on minimal media. The findings from our study highlight the potential of using fast growing S. elongatus isolates with native cyanobacterial promoters for metabolic engineering applications.