Spatiotemporal Gene Repression System in the Heterocyst-Forming Multicellular Cyanobacterium Anabaena sp. PCC 7120

The heterocyst-forming multicellular cyanobacterium Anabaena sp. PCC 7120 is often used as a model organism for prokaryotic cell differentiation. We recently demonstrated that heterocysts are suitable for photosynthetic production of valuable chemicals, such as ethanol, due to their active catabolism and microoxic conditions. We have developed gene regulation systems, including cell type-specific gene induction systems, to broaden this cyanobacterium's use. In the present study, a heterocyst-specific conditional gene repression system was successfully created by combining a cell type-specific gene induction system with CRISPRi technology. We targeted the glnA gene that encodes glutamine synthetase, an essential enzyme for nitrogen assimilation, to reconstruct metabolism in the multicellular cyanobacterium. Heterocyst-specific repression of glnA enhanced ethanol production. We believe that heterocyst-specific gene repression systems are useful tools for basic research on cell differentiation as well as for metabolic engineering of heterocysts.