2026/06/01 by Erik Zimmer, Carolin Poppitz, Stephan Klähn +1 · 1 voice
Biochemistry, Genetics and Molecular Biology · Agricultural and Biological Sciences · #Photosynthetic Processes and Mechanisms #Plant Stress Responses and Tolerance #Microbial Metabolic Engineering and Bioproduction
paper · doi:10.1111/tpj.70974
openalex publication_date 2026/06/01 · openalex created_date 2026/06/10 · openalex updated_date 2026/07/27
SUMMARY Cyanobacteria are photoautotrophic microorganisms that fix CO 2 through oxygenic photosynthesis during the day and rely on heterotrophic metabolism at night. In nature, the availability of inorganic carbon (Ci) is often limited, posing a major constraint on photosynthetic efficiency. To overcome this, cyanobacteria have evolved a sophisticated CO 2 ‐concentrating mechanism (CCM) that enhances the catalytic performance of the primary carboxylating enzyme, ribulose‐1,5‐bisphosphate carboxylase/oxygenase (RubisCO). The CCM functions by elevating intracellular CO 2 concentrations around RubisCO to suppress its oxygenase activity and enhance CO 2 fixation efficiency. Central to this system is the carboxysome, a proteinaceous microcompartment that encapsulates RubisCO and carbonic anhydrase, facilitating efficient conversion of bicarbonate (HCO 3 − ) to CO 2 and its subsequent fixation. This is complemented by multiple Ci transporters that mediate active uptake of CO 2 and HCO 3 − . Five major transport systems have been characterized: two specialized NDH‐1 complexes for CO 2 transport and its conversion into HCO 3 − , and SbtA, BicA, and BCT1 for HCO 3 − uptake. Recent structural studies on CCM uptake systems have revealed key mechanisms of HCO 3 − transport, CO 2 hydration and transport coupling. These insights provided a deeper understanding of how these systems enhance Ci acquisition and maintain photosynthetic efficiency across diverse environmental conditions and various CO 2 regimes. Moreover, the CCM is tightly regulated at both transcriptional and post‐translational levels to balance energy usage and carbon demand. This review outlines our current insights into the molecular architecture, transport dynamics, and regulatory networks of the cyanobacterial CCM, emphasizing its critical role in photosynthesis and its potential as a model for bioengineering enhanced CO 2 fixation or for engineering synthetic bacterial microcompartments.