MINIREVIEW Ecological Aspects of the Distribution of Different Autotrophic CO2 Fixation Pathways

Autotrophic CO2 fixation represents the most important biosynthetic process in biology. Besides the well-known Calvin-Benson cycle, five other totally different autotrophic mechanisms are known today. This mini-review discusses the factors determining their distribution. As will be made clear, the observed diversity reflects the variety of the organisms and the ecological niches existing in nature. Autotrophic CO2 fixation represents the most important biosynthetic process in nature, being responsible for the net fixation of 7 1016 g carbon annually, corresponding to the conservation of 2.8 1018 kJ of energy (107). The photosyn-thetic path of carbon in algae and plants was elucidated in the laboratory of Melvin Calvin in the 1940s and 1950s; the dis-covered reductive pentose phosphate (Calvin-Benson [CB]) cycle was immediately proposed to be the universal au-totrophic carbon dioxide assimilation pathway, and the pres-ence of its key enzyme, ribulose-1,5-bisphosphate carboxylase, was regarded as a synonym for autotrophy. This idea fit per