Global Metabolic Rewiring of an Obligate Photoautotrophic Cyanobacterium for Production of Chemicals Under Diurnal Light Conditions

Chemical production in photosynthetic organisms is a nascent technology with great promise for renewable chemical production. Cyanobacteria are under investigation as a means to utilize light energy to directly recycle CO₂ into renewable chemical compounds currently derived from petroleum. However, while genetic engineering tools are readily available for model organisms such as Escherichia coli and Saccharomyces cerevisiae, this is not the case for cyanobacteria. We have previously engineered production of the chemical feedstock 2,3-butanediol (23BD) from an obligate photoautotrophic cyanobacterium, Synechococcus elongatus PCC 7942. We subsequently explored the optimization of 23BD production by varying ribosomal binding site and promoter strength, operon organization, and gene expression at the transcriptional and translational level. The resulting engineered strains exhibited enhanced total carbon fixation and 23BD production under continuous light conditions. We concurrently observed an increase in oxygen evolution correlating to high carbon redirection away from metabolism, indicating the possibility of an increase in photosynthetic efficiency overall. Any large-scale cyanobacterial production scheme must rely on natural sunlight for energy, thereby limiting production time to only lighted hours during the day. To overcome this limitation we engineered S. elongatus for production of 23BD in continuous light, diurnal light, and continuous dark conditions via supplementation with glucose or xylose. This study achieved efficient 23BD production under diurnal conditions, which was comparable with that under continuous light conditions. These advances in engineering cyanobacteria provide additional tools to understand cyanobacterial metabolism as well as increase the amount of CO₂ converted to valuable chemicals by these microorganisms.