Targeted genome editing of the non-model cyanobacterium Cyanothece PCC 7425 via CRISPR/Cas12a

Cyanobacteria are diverse photosynthetic microorganisms of great interest for fundamental science and sustainable biotechnological applications. However, their polyploidy makes genetic manipulation challenging and time-consuming. The development of CRISPR/Cas tools has greatly accelerated genome editing and metabolic engineering of some cyanobacterial model species. In this work, we extend the CRISPR/Cas12a system for targeted gene deletion in the non-model cyanobacterium Cyanothece sp. PCC 7425, interesting for its ability to perform intracellular calcium carbonate (CaCO₃) biomineralization, nitrogen fixation, etc. We demonstrate for the first time its tractability to gene knockout by generating deletion mutants of four genes (cax3-cax4, gor, and sodB) acting in metabolism and/or response to stresses, using Cas12a-mediated homologous recombination. Importantly, full chromosome segregation was rapidly achieved after a single round of selection in all cases. All mutants were genotypically and phenotypically characterised. Moreover, biochemical analysis in the case of the ΔsodB mutant further confirmed its targeted deletion. Overall, CRISPR/Cas12a provides a rapid and efficient system for genome editing in Cyanothece sp. PCC 7425, establishing this organism as a versatile model for studying oxidative stress pathways, metal toxicity, and moreover, the still poorly known mechanism(s) of intracellular CaCO₃ biomineralization. KEY POINTS: • Rapid and efficient CRISPR/Cas12a editing established in Cyanothece sp. PCC 7425. • Fully segregated knockout mutants obtained after a single selection round. • Platform for exploring the biotechnological potential of Cyanothece sp. PCC 7425.