Six different carbon fixation mechanisms have been identified in autotrophic
organisms; (i) the Calvin–Benson–Bassham (Calvin) cycle, (ii)
the reductive citric acid cycle, (iii) the reductive acetyl-coenzyme A pathway,
(iv) the 3-hydroxypropionate bicycle, (v) the hydroxypropionate–
hydroxybutyrate cycle, and (vi) the dicarboxylate–hydroxybutyrate
cycle [11]. Themain carbon fixation cycle used for primary biomass production
(including in cyanobacteria) is the Calvin cycle [12], and
cyanobacteria contribute to almost a quarter of the global carbon fixation