Crassulacean Acid Metabolism (CAM) is a specialized photosynthetic pathway predominantly observed in plants, but certain cyanobacteria exhibit similar metabolic adaptations to optimize carbon fixation under fluctuating environmental conditions. CAM operates in two phases: the dark phase and the light phase, allowing organisms to conserve water and improve carbon efficiency. During the dark phase, CO₂ is taken up and fixed into organic acids, such as malate, which are stored in vacuole-like structures or cytoplasmic pools. This is facilitated by the enzyme phosphoenolpyruvate carboxylase (PEPC). In the light phase, the stored organic acids are decarboxylated to release CO₂, which is then refixed by the Calvin-Benson cycle in the presence of light-driven ATP and NADPH generation via photosynthesis. This temporal separation of CO₂ uptake and utilization allows CAM-adapted cyanobacteria to thrive in environments with limited water availability or high salinity, where daytime stomatal opening (or equivalent carbon uptake processes) would lead to excessive water loss. While CAM-like pathways in bacteria are less well understood compared to plants, they represent an important ecological adaptation for survival in extreme habitats.

CAM (Crassulacean acid metabolism), dark References