The cbb operon is crucial for carbon dioxide fixation through the Calvin-Benson-Bassham (CBB) cycle. This operon is encoded in duplicate within the genome, consisting of several genes that work together to facilitate CO2 uptake and conversion into organic compounds. CbbL encodes for the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), the key enzyme in the CBB cycle that catalyzes CO2 fixation. CbbS encodes for the small subunit of RuBisCO, which pairs with the large subunit to form the functional enzyme. cbbX is believed to be involved in the regulation of the CBB cycle and plays a role in the assembly and stability of the RuBisCO complex. CbbR encodes the transcription regulator CbbR,which activates or represses the cbb operon in response to phosphoenolpyruvate (PEP) levels, by binding to specific sites near the cbb promoter. When PEP levels are high, CbbR represses cbb operon transcription and activates its transcription when PEP levels are low. The operon’s expression is additionally influenced by RegA which forms part of the RegA/RegB global transcription regulation system, which enhances the cbb operon’s promoter activity.

Calvin–Benson–Bassham (CBB) cycle (cbb operon activation) References