Overexpression of β-carboxysomes increases photosynthesis and growth in <i>Synechocystis</i> sp. PCC 6803

Cyanobacteria are photoautotrophic cell factories capable of converting carbon dioxide into valuable chemicals. The rate-limiting step in photosynthesis is the enzymatic carbon fixation catalyzed by Rubisco. The carboxysome is a protein-based organelle that plays a central role in cyanobacterial carbon fixation. It consists of thousands of subunits, including hexameric and pentameric proteins, which form a shell to encapsulate the enzymes Rubisco and carbonic anhydrase. Here, we enhanced β-carboxysome biogenesis in Synechocystis sp. PCC 6803 by overexpressing a full or partial set of endogenous β-carboxysome components. Overexpression of carboxysome proteins altered protein stoichiometry, morphology, and cellular abundance of β-carboxysomes, as well as improved photosynthetic activities and cell growth. These findings indicate that targeted carboxysome overexpression enhances photosynthetic efficiency and growth of cyanobacteria under favorable conditions. This study provides a framework for engineering cyanobacterial chassis cells as microbial cell factories and carboxysome-based CO2-concentrating mechanisms in heterologous hosts, including crop plants, to improve photosynthetic productivity for sustainable bioproduction.