Base Editing for Reprogramming Cyanobacterium Synechococcus elongatus

Global climate change demands carbon-negative innovations to reduce the concentration of atmospheric carbon dioxide (CO2). Cyanobacteria can fix CO2 from the atmosphere and can be genetically reprogrammed for the production of biofuels, chemicals and food products, making an ideal microbial chassis for carbon-negative biotechnology. However, the progress seems to be slowed down due to the lagging-behind synthetic biology toolkits, especially the CRISPR-Cas-based genome-editing tools. As such, we developed a base-editing tool based on the CRISPR-Cas system and deamination for cyanobacterium Synechococcus elongatus. We achieved efficient and precise genome editing at a single-nucleotide resolution, and identified the pure population of edited cells at the first round of selection without extra segregation. By using the base-editing tool, we successfully manipulated the glycogen metabolic pathway via the introduction of premature STOP codons to inactivate the corresponding genes. We demonstrated multiplex base editing by editing two genes at once, obtaining a nearly two-fold increase in the glycogen content. We present here the first report of base editing in the phylum of cyanobacteria, and a paradigm for applying CRISPR-Cas systems in bacteria. We believe that this work will accelerate the synthetic biology of cyanobacteria and drive more innovations to alleviate global climate change.