Table 1.

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

Pathway	Associated taxaa	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, 103–105]	Yes
rTCA	Aquificae [106]  Aquificales Chlorobi [107]  Chlorobiales Nitrospirae [108]  autotrophs Proteobacteria  Magnetococcus sp. MC-1  Desulfobacter hydrogenophilus	~1	~2 to 23	[44, 45, 103–105]	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 glycinec	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, 117–121], and O₂ sensitivity data from Berg [122].

^cRecently proposed pathway for the Deltaproteobacterium Candidatus Phosphitivorax anaerolimi [36].