The Calvin-Benson cycle, also known as the reductive pentose phosphate cycle, is a central pathway for carbon fixation in bacteria, particularly in photoautotrophs and chemoautotrophs. This cycle enables bacteria to convert inorganic carbon dioxide (CO₂) into organic molecules, primarily glyceraldehyde-3-phosphate (G3P), which serves as a precursor for glucose and other essential cellular components. The cycle begins with the carboxylation of ribulose-1,5-bisphosphate (RuBP) by the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), producing two molecules of 3-phosphoglycerate (3-PGA). These molecules are then phosphorylated and reduced using ATP and NADPH, respectively, to generate G3P. Part of the G3P is used to regenerate RuBP through a series of reactions involving sugar phosphate intermediates, while the remainder can be directed toward biosynthesis pathways. The Calvin-Benson cycle is energetically demanding, requiring significant input of ATP and NADPH, often supplied by photosynthesis in phototrophic bacteria or oxidation of inorganic compounds in chemolithoautotrophs. This pathway is essential for autotrophic bacterial growth and plays a key role in global carbon cycling by converting atmospheric CO₂ into biomass, contributing to primary productivity in diverse ecosystems.

Calvin-Benson cycle References