Carbon Fixation Pathways: Mechanisms and Organisms

This lecture discusses various pathways for carbon dioxide fixation, focusing on the mechanisms and organisms involved. The instructor begins by reviewing the Calvin-Benson-Bassham cycle and the reductive citric acid cycle, highlighting their significance in photosynthesis. The lecture then introduces the hydroxypropionate bi-cycle, detailing its two-part structure and the role of acetyl-CoA and bicarbonate in the process. The instructor explains the biochemical transformations that occur, including the reduction of malonyl-CoA and the formation of hydroxypropionate. The discussion extends to the dicarboxylate/4-hydroxybutyrate cycle, emphasizing its anaerobic nature and the organisms that utilize these pathways. The instructor also addresses the evolutionary aspects of these cycles, noting their adaptation to different environmental conditions. Throughout the lecture, the importance of understanding these pathways in the context of biogeochemistry and microbial ecology is underscored, providing insights into how various organisms fix carbon in diverse habitats.