Table 1.

Comparative description of the natural and synthetic carbon fixation pathways: microorganism examples, energy sources, necessary inputs, products of the cycle, reducing agents, main enzymes, and sensitivity of the enzymes to oxygen.

Pathway	Status	Organisms	Energy Source	Input	Output	Reductants	Key Enzyme	O2 Sensitive	References
Calvin-Benson	Natural	Plants, Algae, Cyanobacteria, Aerobic Proteobacteria, Purple bacteria	Light	3 CO2, 9 ATP,6 NAD(P)H	Glyceraldehyde-3-phosphate	NAD(P)H	RuBisCO	No	[23]
rTCA	Natural	Green sulfur bacteria, Proteobacteria, Aquificae, Nitrospirae	Light and Sulfur	2 CO2, 2 ATP,4 NAD(P)H	Pyruvate	NAD(P)H and ferredoxin	2-Oxoglutarate synthase, Isocitrate dehydrogenase	Yes	[54]
Wood–Ljungdahl	Natural	Acetogenic, Methanogenic Archaea, Planctomycetes, Sulfate, Archaeoglobales	Hydrogen	2 CO2, 1 ATP, 4 NAD(P)H	Acetyl-CoA	Ferredoxin	NAD-independent formate dehydrogenase, Acetyl-CoA synthase-CO dehydrogenase	Yes	[9]
3-HP	Natural	Chloroflexaceae	Light	3 HCO3−, 5 ATP, 5 NAD(P)H	Pyruvate	NAD(P)H	Acetyl-CoA carboxylase, Propionyl-CoA carboxylase	No	[72], [187]
HP/HB	Natural	Aerobic Sulfolobales	Hydrogen and Sulfur	2 HCO3−, 4 ATP, 4 NAD(P)H	Acetyl-CoA	NAD(P)H	Acetyl-CoA-Propionyl-CoA carboxylase	No	[78]
DC/HB	Natural	Anaerobic Thermoproteale, Desulfurococcales	Hydrogen and Sulfur	1 CO2, 1 HCO3−, 3 ATP, 4 NAD(P)H	Acetyl-CoA	NAD(P)H and Ferredoxin	Pyruvate synthase, PEP carboxylase	Yes	[79]
RHP	Candidate Natural	Methanospirillum hungatei	Hydrogen	CO2, 3 ATP, 2 NAD(P)H	Gluconeogenesis and glycolysis	NAD(P)H	RuBisCO	No	[11]
Natural Reductive Glycine	Candidate Natural	Candidatus phosphitivorax anaerolimiDesulfovibrio desulfuricans	Phosphite	CO2, ATP, NAD(P)H	Formate/ Pyruvate	NAD(P)H and ferredoxin	CO2-reducing formate dehydrogenase (fdhAB)	–	[92]
Reverse oTCA	Candidate Natural	Desulfurella acetivorans	Hydrogen	CO2, ATP, NAD(P)H	Acetyl-CoA	Ferredoxin	Citrate synthase	–	[12]
CETCH	Synthetic	Theoretical	–	2 CO2, 2 ATP, 3 NAD(P)H	Glyoxylate	NAD(P)H	CoA- dependent carboxylase	No	[104]
Reductive Glycine	Synthetic	Demonstrated in E. coli as host	–	CO2, NADH	Pyruvate	Ferredoxin	Glycine cleavage system	No	[93]
Synthetic malyl-CoA-glycerate	Synthetic	Demonstrated in E. coli and Synechococcus elongatus PCC7942 host	–	CO2, 3 ATP, 3 NADH	Acetyl-CoA	NAD(P)H	PEP-carboxylase, RuBisCO	No	[119]
SACA Pathway	Synthetic	Demonstrated in E. coli as host	–	CO2	Acetyl-CoA	–	NAD-independent formate dehydrogenase	No	[6]
Formolase pathway	Synthetic	Theoretical	–	CO2, NADH, ATP	Dihydroxyacetone-phosphate	NADH	NAD-independent formate dehydrogenase	No	[5]