Table 1 Isotopic discrimination, productivity, and O₂ sensitivity of extant carbon fixation pathways.

Pathway	Associated taxa^a	Modern productivity (Pg C/yr)^b	¹³C/¹²C isotope discrimination Δδ¹³C (‰)	Isotope discrimination references	Pathway O₂ sensitive?^b
CBB	Cyanobacteria [97] Eukaryota [98, 99] photoautotrophs Proteobacteria [100] autotrophic Alpha-, Beta-, Gammaproteobacteria Chloroflexi [101] Oscillochloridaceae Firmicutes [102] Sulfobacillus spp.	~100	~10 to 35	[26, 44, 45, 103,104,105]	Yes
rTCA	Aquificae [106] Aquificales Chlorobi [107] Chlorobiales Nitrospirae [108] autotrophs Proteobacteria Magnetococcus sp. MC-1 Desulfobacter hydrogenophilus	~1	~2 to 23	[44, 45, 103,104,105]	Yes
roTCA	Aquificae Thermosulfidibacter takaii Proteobacteria sulfur-reducing Deltaproteobacteria	Unknown	Unknown	N/A	Unknown
HP/HB	Crenarchaeota [109] Sulfolobales Marine group I [110] Thaumarchaeota [111]	~0.7	~0 to 4	[44]	No
Wood–Ljungdahl	Euryarchaeota [112] Archaeoglobales methanogens Firmicutes acetogens Planctomycetes [113] anaerobic ammonium-oxidizers Proteobacteria autotrophic Deltaproteobacteria Spirochaetes [113] Treponema primitia	~0.1	~5 to 80	[45, 46, 50, 51, 53, 114]	Yes
DC/HB	Crenarchaeota Thermoproteales Desulfurococcales	<0.1	~0 to 4	[44, 45]	Yes
3HP	Chloroflexi Chloroflexaceae	<0.1	~0 to 14	[20, 44, 115]	No
Reductive glycine^c	Proteobacteria Candidatus Phosphitivorax anaerolimi	<0.1	Unknown	N/A	Unknown

Isotopic discrimination reported from literature, calculated as Δδ¹³C = δ¹³C_product − δ¹³C_reactant, where product is biomass (or acetate/methane for acetogens/methanogens, respectively, utilizing the Wood–Ljungdahl pathway) and reactant is source carbon in growth media.
CBB Calvin–Benson–Bassham cycle, DC/HB dicarboxylate–4-hydroxybutyrate cycle, HP/HB 3-Hydroxyproprionate/4-hydroxybutyrate cycle, roTCA reverse oxidative tricarboxylic acid cycle, rTCA reductive citric acid cycle, 3HP 3-hydroxyproprionate bicycle.
^aAssociated taxa from Berg et al. [37], Hugler and Sievert [116], Ward and Shih [25], and references therein. References for definitions of informal taxonomic groups are listed within the table at first instance. Listed taxa are not necessarily diagnostic of each pathway, but rather describe major groups of organisms where pathway can be found.
^bModern productivity values from [38, 117,118,119,120,121], and O₂ sensitivity data from Berg [122].
^cRecently proposed pathway for the Deltaproteobacterium Candidatus Phosphitivorax anaerolimi [36].

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