Microbial Conversion and Utilization of CO2

Rising greenhouse gas emissions have contributed to unprecedented levels of climate change, while microbial conversion and utilization of CO2 is a practical way to reduce emissions and promote green manufacturing. This article mainly summarizes several natural CO2 pathways that have been discovered, including the Calvin cycle, the reduced tricarboxylic acid (rTCA) cycle, the Wood–Ljungdahl (WL) pathway, the 3-hydroxypropionate/4-hydroxybutyrate (HP/HB) cycle, the dicarboxylate/4-hydroxybutyrate (DC/HB) cycle, the 3-hydroxypropionate (3HP) cycle, the reductive glycine (rGly) pathway, and artificially designed carbon fixation pathways includes the CETCH cycle, the MOG pathway, the acetyl-CoA bicycle, and the POAP cycle. We also discussed applications of different carbon fixation enzymes, notably ribulose-1, 5-diphosphate carboxylase/oxygenase, pyruvate carboxylase, carbonic anhydrase, as well as formate dehydrogenase. This paper further addressed the development of photosynthetic autotrophs, chemergic autotrophs and model bacteria Escherichia coli or yeast produced main products for CO2 fixation through metabolic engineering, such as alcohols, organic acids, fatty acids and lipids, bioplastics, terpenoids, hydrocarbons, and biomass. Future studies on CO2 microbial conversion should focus on improving the efficiency of carbon fixation enzymes, metabolic modules of the carbon sequestration pathway, and intracellular energy utilization. Coupled microbial and electrochemical methods for CO2 fixation, in addition to biological fixation, show considerable promise.