Carbon fixation or сarbon assimilation is the process by which inorganic carbon (particularly in the form of carbon dioxide) is converted to organic compounds by living organisms. The organic compounds are then used to store energy and as building blocks for other important biomolecules. The most prominent example of carbon fixation is photosynthesis; another form known as chemosynthesis can take place in the absence of sunlight.
Organisms that grow by fixing carbon are called autotrophs, which include photoautotrophs (which use sunlight), and lithoautotrophs (which use inorganic oxidation). Heterotrophs are not themselves capable of carbon fixation but are able to grow by consuming the carbon fixed by autotrophs. "Fixed carbon", "reduced carbon", and "organic carbon" may all be used interchangeably to refer to various organic compounds.
Net vs. gross CO2 fixationEdit
It is estimated that approximately 258 billion tons of carbon dioxide are converted by photosynthesis annually. The majority of the fixation occurs in marine environments, especially areas of high nutrients. The gross amount of carbon dioxide fixed is much larger since approximately 40% is consumed by respiration following photosynthesis. Given the scale of this process, it is understandable that RuBisCO is the most abundant protein on Earth.
Overview of pathwaysEdit
Six autotrophic carbon fixation pathways are known as of 2011. The Calvin cycle fixes carbon in the chloroplasts of plants and algae, and in the cyanobacteria. It also fixes carbon in the anoxygenic photosynthesis in one type of proteobacteria called purple bacteria, and in some non-phototrophic proteobacteria.
Of the five other autotrophic pathways, two are known only in bacteria (the reductive citric acid cycle and the 3-hydroxypropionate cycle), two only in archaea (two variants of the 3-hydroxypropionate cycle), and one in both bacteria and archaea (the reductive acetyl CoA pathway).
In photosynthesis, energy from sunlight drives the carbon fixation pathway. Oxygenic photosynthesis is used by the primary producers—plants, algae, and cyanobacteria. They contain the pigment chlorophyll, and use the Calvin cycle to fix carbon autotrophically. The process works like this:
- 2H2O → 4e− + 4H+ + O2
- CO2 + 4e− + 4H+ → CH2O + H2O
In the first step, water is dissociated into electrons, protons, and free oxygen. This allows the use of water, one of the most abundant substances on Earth, as an electron donor—as a source of reducing power. The release of free oxygen is a side-effect of enormous consequence. The first step uses the energy of sunlight to oxidize water to O2, and, ultimately, to produce ATP
- ADP + Pi ⇌ ATP + H2O
and the reductant, NADPH
- NADP+ + 2e− + 2H+ ⇌ NADPH + H+
In the second step, called the Calvin cycle, the actual fixation of carbon dioxide is carried out. This process consumes ATP and NADPH. The Calvin cycle in plants accounts for the preponderance of carbon fixation on land. In algae and cyanobacteria, it accounts for the preponderance of carbon fixation in the oceans. The Calvin cycle converts carbon dioxide into sugar, as triose phosphate (TP), which is glyceraldehyde 3-phosphate (GAP) together with dihydroxyacetone phosphate (DHAP):
- 3 CO2 + 12 e− + 12 H+ + Pi → TP + 4 H2O
An alternative perspective accounts for NADPH (source of e−) and ATP:
- 3 CO2 + 6 NADPH + 6 H+ + 9 ATP + 5 H2O → TP + 6 NADP+ + 9 ADP + 8 Pi
The formula for inorganic phosphate (Pi) is HOPO32− + 2H+. Formulas for triose and TP are C2H3O2-CH2OH and C2H3O2-CH2OPO32− + 2H+
Somewhere between 3.8 and 2.3 billion years ago, the ancestors of cyanobacteria evolved oxygenic photosynthesis, enabling the use of the abundant yet relatively oxidized molecule H2O as an electron donor to the electron transport chain of light-catalyzed proton-pumping responsible for efficient ATP synthesis. When this evolutionary breakthrough occurred, autotrophy (growth using inorganic carbon as the sole carbon source) is believed to have already been developed. However, the proliferation of cyanobacteria, due to their novel ability to exploit water as a source of electrons, radically altered the global environment by oxygenating the atmosphere and by achieving large fluxes of CO2 consumption.
CO2 concentrating mechanismsEdit
Many photosynthetic organisms have not acquired CO2 concentrating mechanisms (CCMs), which increase the concentration of CO2 available to the initial carboxylase of the Calvin cycle, the enzyme RuBisCO. The benefits of a CCM include increased tolerance to low external concentrations of inorganic carbon, and reduced losses to photorespiration. CCMs can make plants more tolerant of heat and water stress.
- HCO3− + H+ ⇌ CO2 + H2O
Lipid membranes are much less permeable to bicarbonate than to CO2. To capture inorganic carbon more effectively, some plants have adapted the anaplerotic reactions
- HCO3− + H+ + PEP → OAA + Pi
CAM plants that use Crassulacean acid metabolism as an adaptation for arid conditions. CO2 enters through the stomata during the night and is converted into the 4-carbon compound, malic acid, which releases CO2 for use in the Calvin cycle during the day, when the stomata are closed. The dung jade plant (Crassula ovata) and cacti are typical of CAM plants. Sixteen thousand species of plants use CAM. These plants have a carbon isotope signature of −20 to −10 ‰.
C4 plants preface the Calvin cycle with reactions that incorporate CO2 into one of the 4-carbon compounds, malic acid or aspartic acid. C4 plants have a distinctive internal leaf anatomy. Tropical grasses, such as sugar cane and maize are C4 plants, but there are many broadleaf plants that are C4. Overall, 7600 species of terrestrial plants use C4 carbon fixation, representing around 3% of all species. These plants have a carbon isotope signature of −16 to −10 ‰.
The large majority of plants are C3 plants. They are so-called to distinguish them from the CAM and C4 plants, and because the carboxylation products of the Calvin cycle are 3-carbon compounds. They lack C4 dicarboxylic acid cycles, and therefore have higher CO2 compensation points than CAM or C4 plants. C3 plants have a carbon isotope signature of −24 to −33‰.
Bacteria and cyanobacteriaEdit
Almost all cyanobacteria and some bacteria utilize carboxysomes to concentrate carbon dioxide. Carboxysomes are protein shells filled with the enzyme RuBisCO and a carbonic anhydrase. The carbonic anhydrase produces CO2 from the bicarbonate that diffuses into the carboxysome. The surrounding shell provides a barrier to carbon dioxide loss, helping to increase its concentration around RuBisCO.
Other autotrophic pathwaysEdit
Reverse Krebs cycleEdit
The reverse Krebs cycle, also known as reverse TCA cycle (rTCA) or reductive citric acid cycle, is an alternative to the standard Calvin-Benson cycle for carbon fixation. It has been found in strict anaerobic or microaerobic bacteria (as Aquificales) and anaerobic archea. It was discovered by Evans, Buchanan and Arnon in 1966 working with the photosynthetic green sulfur bacterium Chlorobium limicola. The cycle involves the biosynthesis of acetyl-CoA from two molecules of CO2. The key steps of the reverse Krebs cycle are:
- Succinate to succinyl-CoA, an ATP dependent step
- Succinyl-CoA to alpha-ketoglutarate, using one molecule of CO2
- Citrate converted into oxaloacetate and acetyl-CoA, this is an ATP dependent step and the key enzyme is the ATP citrate lyase
This pathway is cyclic due to the regeneration of the oxaloacetate.
The reverse Krebs cycle is used by microorganisms in anaerobic environments. In particular, it is one of the most used pathways in hydrothermal vents by the Epsilonproteobacteria. This feature is very important in oceans. Without it, there would be no primary production in aphotic environments, which would lead to habitats without life. So this kind of primary production is called "dark primary production".
One other important aspect is the symbiosis between Gammaproteobacteria and Riftia pachyptila. These bacteria can switch from the Calvin-Benson cycle to the rTCA cycle and vice versa in response to different concentrations of H2S in the environment.
Reductive acetyl CoA pathwayEdit
The reductive acetyl CoA pathway (CoA) pathway, also known as the Wood-Ljungdahl pathway, was discovered by Harland G. Wood and Lars G. Ljungdahl in 1965, thanks to their studies on Clostridium thermoaceticum, a Gram positive bacterium now named Moorella thermoacetica. It is an acetogen, an anaerobic bacteria that uses CO2 as electron acceptor and carbon source, and H2 as an electron donor to form acetic acid. This metabolism is wide spread within the phylum Firmicutes, especially in the Clostridia.
The pathway is also used by methanogens, which are mainly Euryarchaeota, and several anaerobic chemolithoautotrophs, such as sulfate-reducing bacteria and archaea. It is probably performed also by the Brocadiales, an order of Planctomycetes that oxidize ammonia in anaerobic condition. Hydrogenotrophic methanogenesis, which is only found in certain archaea and accounts for 80% of global methanogenesis, is also based on the reductive acetyl CoA pathway.
One branch of this pathway, the methyl branch, is similar but non-homologous between bacteria and archaea. In this branch happens the reduction of CO2 to a methyl residue bound to a cofactor. The intermediates are formate for bacteria and formyl-methanofuran for archaea, and also the carriers, tetrahydrofolate and tetrahydropterins respectively in bacteria and archaea, are different, such as the enzymes forming the cofactor-bound methyl group.
Otherwise, the carbonyl branch is homologous between the two domains and consists of the reduction of another molecule of CO2 to a carbonyl residue bound to an enzyme, catalyzed by the CO dehydrogenase/acetyl-CoA synthase. This key enzyme is also the catalyst for the formation of acetyl-CoA starting from the products of the previous reactions, the methyl and the carbonyl residues.
This carbon fixation pathway requires only one molecule of ATP for the production of one molecule of pyruvate, which makes this process one of the main choice for chemolithoautotrophs limited in energy and living in anaerobic conditions
The 3-Hydroxypropionate bicycle, also known as 3-HP/malyl-CoA cycle, was discovered by Helge Holo in 1989. It's a pathway of carbon fixation and is utilized by green non-sulfur phototrophs of Chloroflexaceae family, including the maximum exponent of this family Chloroflexus auranticus by which this way was discovered and demonstrated.
The 3-Hydroxipropionate bicycle is composed of two cycles and the name of this way comes from the 3-Hydroxyporopionate which corresponds to an intermediate characteristic of it.
The first cycle is a way of synthesis of glycoxilate. During this cycle two bicarbonate molecules are fixed thanks to the action of two enzymes: the Acetyl-CoA carboxylase catalyzes the carboxylation of the Acetyl-CoA to Malonyl-CoA and Propionyl-CoA carboxylase catalyses the carboxylation of Propionyl-CoA to Methylamalonyl-CoA. From this point a series of reactions lead to the formation of glycoxylate which will thus become part of the second cycle.
In the second cycle, glycoxilate is approximately one molecule of Propionyl-CoA forming Methylamalonyl-CoA. This, in turn, is then converted through a series of reactions into Citramalyl-CoA. The Citramalyl-CoA is split into pyruvate and Acetyl-CoA thanks to the enzyme MMC lyase. At this point the pyruvate is released, while the Acetyl-CoA is reused and carboxylated again at Malonyl-coa thus reconstituting the cycle.
19 are the total reactions involved in 3-Hydroxypropionate bicycle and 13 are the multifunctional enzymes used. The multifunctionality of these enzymes is an important feature of this pathway which thus allows the fixation of 3 bicarbonate molecules.
It is a very expensive way: 7 ATP molecules are used for the synthesis of the new pyruvate and 3 ATP for the phosphate triose.
A variant of the 3-hydroxypropionate cycle was found to operate in the aerobic extreme thermoacidophile archaeon Metallosphaera sedula. This pathway is called the 3-hydroxypropionate/4-hydroxybutyrate cycle.
Yet another variant of the 3-hydroxypropionate cycle is the dicarboxylate/4-hydroxybutyrate cycle. It was discovered in anaerobic archaea. It was proposed in 2008 for the hyperthermophile archeon Ignicoccus hospitalis.
Chemosynthesis is carbon fixation driven by energy obtained by oxidating inorganic substances (e.g., hydrogen gas or hydrogen sulfide), rather than from sunlight. Sulfur- and hydrogen-oxidizing bacteria often use the Calvin cycle or the reductive citric acid cycle.
Although almost all heterotrophs cannot synthesize complete organic molecules from carbon dioxide, some carbon dioxide is incorporated in their metabolism. Notably pyruvate carboxylase consumes carbon dioxide (as bicarbonate ions) as part of gluconeogenesis, and carbon dioxide is consumed in various anaplerotic reactions.
Carbon isotope discriminationEdit
Some carboxylases, particularly RuBisCO, preferentially bind the lighter carbon stable isotope carbon-12 over the heavier carbon-13. This is known as carbon isotope discrimination and results in carbon-12 to carbon-13 ratios in the plant that are higher than in the free air. Measurement of this ratio is important in the evaluation of water use efficiency in plants, and also in assessing the possible or likely sources of carbon in global carbon cycle studies.
- Geider, R. J.; et al. (2001). "Primary productivity of planet earth: biological determinants and physical constraints in terrestrial and aquatic habitats". Global Change Biol. 7 (8): 849–882. Bibcode:2001GCBio...7..849G. doi:10.1046/j.1365-2486.2001.00448.x.
- Swan BK, Martinez-Garcia M, Preston CM, Sczyrba A, Woyke T, Lamy D, Reinthaler T, Poulton NJ, Masland ED, Gomez ML, Sieracki ME, DeLong EF, Herndl GJ, Stepanauskas R (2011). "Potential for chemolithoautotrophy among ubiquitous bacteria lineages in the dark ocean". Science. 333 (6047): 1296–300. Bibcode:2011Sci...333.1296S. doi:10.1126/science.1203690. PMID 21885783. S2CID 206533092.
- Cardona T, Sánchez-Baracaldo P, Rutherford AW, Larkum AW (November 2018). "Early Archean origin of Photosystem II". Geobiology. 0 (2): 127–150. doi:10.1111/gbi.12322. PMC 6492235. PMID 30411862.
- Cardona T, Murray JW, Rutherford AW (May 2015). "Origin and Evolution of Water Oxidation before the Last Common Ancestor of the Cyanobacteria". Molecular Biology and Evolution. 32 (5): 1310–28. doi:10.1093/molbev/msv024. PMC 4408414. PMID 25657330.
- Brasier M, McLoughlin N, Green O, Wacey D (June 2006). "A fresh look at the fossil evidence for early Archaean cellular life". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 361 (1470): 887–902. doi:10.1098/rstb.2006.1835. PMC 1578727. PMID 16754605.
- Tomitani A, Knoll AH, Cavanaugh CM, Ohno T (April 2006). "The evolutionary diversification of cyanobacteria: molecular-phylogenetic and paleontological perspectives". Proceedings of the National Academy of Sciences of the United States of America. 103 (14): 5442–7. Bibcode:2006PNAS..103.5442T. doi:10.1073/pnas.0600999103. PMC 1459374. PMID 16569695.
- Kopp RE, Kirschvink JL, Hilburn IA, Nash CZ (August 2005). "The Paleoproterozoic snowball Earth: a climate disaster triggered by the evolution of oxygenic photosynthesis". Proceedings of the National Academy of Sciences of the United States of America. 102 (32): 11131–6. Bibcode:2005PNAS..10211131K. doi:10.1073/pnas.0504878102. PMC 1183582. PMID 16061801.
- Dodd AN, Borland AM, Haslam RP, Griffiths H, Maxwell K (2002). "Crassulacean acid metabolism: plastic, fantastic". J. Exp. Bot. 53 (369): 569–580. doi:10.1093/jexbot/53.369.569. PMID 11886877.
- O'Leary MH (1988). "Carbon isotopes in photosynthesis". BioScience. 38 (5): 328–336. doi:10.2307/1310735. JSTOR 1310735. S2CID 29110460.
- Sage RF, Meirong L, Monson RK (1999). "16. The Taxonomic Distribution of C4 Photosynthesis". In Sage RF, Monson RK (eds.). C4 Plant Biology. pp. 551–580. ISBN 0-12-614440-0.
- Wächtershäuser, G. Before enzymes and templates: theory of surface metabolism. OCLC 680443998.
- Fuchs, Georg (13 October 2011). "Alternative Pathways of Carbon Dioxide Fixation: Insights into the Early Evolution of Life?". Annual Review of Microbiology. 65 (1): 631–658. doi:10.1146/annurev-micro-090110-102801. ISSN 0066-4227. PMID 21740227.
- Hügler, Michael; Sievert, Stefan M. (15 January 2011). "Beyond the Calvin Cycle: Autotrophic Carbon Fixation in the Ocean". Annual Review of Marine Science. 3 (1): 261–289. Bibcode:2011ARMS....3..261H. doi:10.1146/annurev-marine-120709-142712. ISSN 1941-1405. PMID 21329206. S2CID 44800487.
- Buchanan, Bob B.; Arnon, Daniel I. (1990). "A reverse KREBS cycle in photosynthesis: consensus at last". Photosynthesis Research. 24 (1): 47–53. doi:10.1007/bf00032643. ISSN 0166-8595. PMID 24419764. S2CID 2753977.
- Grzymski, J. J.; Murray, A. E.; Campbell, B. J.; Kaplarevic, M.; Gao, G. R.; Lee, C.; Daniel, R.; Ghadiri, A.; Feldman, R. A.; Cary, S. C. (5 November 2008). "Metagenome analysis of an extreme microbial symbiosis reveals eurythermal adaptation and metabolic flexibility". Proceedings of the National Academy of Sciences. 105 (45): 17516–17521. Bibcode:2008PNAS..10517516G. doi:10.1073/pnas.0802782105. ISSN 0027-8424. PMC 2579889. PMID 18987310.
- Baltar, Federico; Herndl, Gerhard J. (11 June 2019). "Is dark carbon fixation relevant for oceanic primary production estimates?" (PDF). doi:10.5194/bg-2019-223. Cite journal requires
- Markert, Stephanie Arndt, Cordelia Felbeck, Horst Becher, Dorte Sievert, Stefan M. Hugler, Michael Albrecht, Dirk Robidart, Julie Bench, Shellie Feldman, Robert A. Hecker, Michael Schweder, Thomas (28 February 2007). Physiological proteomics of the uncultured endosymbiont of Riftia pachyptila. OCLC 655249163. PMID 17218528.CS1 maint: multiple names: authors list (link)
- Ljungdahl, L; Wood, HG (1965). "Incorporation of C-14 from carbon dioxide into sugar phosphates, carboxylic acids, and amino acids by Clostridium thermoaceticum". J. Bacteriol. 89 (4): 1055–64. doi:10.1128/jb.89.4.1055-1064.1965. PMC 277595. PMID 14276095.
- Drake, Harold L.; Gößner, Anita S.; Daniel, Steven L. (26 March 2008). "Old Acetogens, New Light". Annals of the New York Academy of Sciences. 1125 (1): 100–128. Bibcode:2008NYASA1125..100D. doi:10.1196/annals.1419.016. ISSN 0077-8923. PMID 18378590. S2CID 24050060.
- Ljungdahl, L G; Wood, H G (1969). "Total Synthesis of Acetate From CO2 by Heterotrophic Bacteria". Annual Review of Microbiology. 23 (1): 515–538. doi:10.1146/annurev.mi.23.100169.002503. ISSN 0066-4227. PMID 4899080.
- Ljungdahl, L. (1 January 1986). "The Autotrophic Pathway of Acetate Synthesis in Acetogenic Bacteria". Annual Review of Microbiology. 40 (1): 415–450. doi:10.1146/annurev.micro.40.1.415. ISSN 0066-4227. PMID 3096193.
- Ljungdahl, Lars G. (2009). "A Life with Acetogens, Thermophiles, and Cellulolytic Anaerobes". Annual Review of Microbiology. 63 (1): 1–25. doi:10.1146/annurev.micro.091208.073617. ISSN 0066-4227. PMID 19575555.
- Jansen, Kathrin; Thauer, Rudolf K.; Widdel, Fritz; Fuchs, Georg (1984). "Carbon assimilation pathways in sulfate reducing bacteria. Formate, carbon dioxide, carbon monoxide, and acetate assimilation by Desulfovibrio baarsii". Archives of Microbiology. 138 (3): 257–262. doi:10.1007/bf00402132. ISSN 0302-8933. S2CID 8587232.
- Zeikus, J.; Kerby, R; Krzycki, J. (8 March 1985). "Single-carbon chemistry of acetogenic and methanogenic bacteria". Science. 227 (4691): 1167–1173. Bibcode:1985Sci...227.1167Z. doi:10.1126/science.3919443. ISSN 0036-8075. PMID 3919443.
- Schauder, Rolf; Preuss, Andrea; Jetten, Mike; Fuchs, Georg (1989). "Oxidative and reductive acetyl CoA/carbon monoxide dehydrogenase pathway in Desulfobacterium autotrophicum". Archives of Microbiology. 151 (1): 84–89. doi:10.1007/bf00444674. ISSN 0302-8933.
- Fuchs, Georg (1994), "Variations of the Acetyl-CoA Pathway in Diversely Related Microorganisms That Are Not Acetogens", Acetogenesis, Springer US, pp. 507–520, doi:10.1007/978-1-4615-1777-1_19, ISBN 978-1-4613-5716-2
- Vorholt, Julia; Kunow, Jasper; Stetter, Karl O.; Thauer, R. K. (1 February 1995). "Enzymes and coenzymes of the carbon monoxide dehydrogenase pathway for autotrophic CO2 fixation in Archaeoglobus lithotrophicus and the lack of carbon monoxide dehydrogenase in the heterotrophic A. profundus". Archives of Microbiology. 163 (2): 112–118. doi:10.1007/s002030050179. ISSN 0302-8933.
- Strous, Marc; Pelletier, Eric; Mangenot, Sophie; Rattei, Thomas; Lehner, Angelika; Taylor, Michael W.; Horn, Matthias; Daims, Holger; Bartol-Mavel, Delphine; Wincker, Patrick; Barbe, Valérie (2006). "Deciphering the evolution and metabolism of an anammox bacterium from a community genome". Nature. 440 (7085): 790–794. Bibcode:2006Natur.440..790S. doi:10.1038/nature04647. ISSN 0028-0836. PMID 16598256. S2CID 4402553.
- Pezacka, E.; Wood, H. G. (1 October 1984). "Role of carbon monoxide dehydrogenase in the autotrophic pathway used by acetogenic bacteria". Proceedings of the National Academy of Sciences. 81 (20): 6261–6265. Bibcode:1984PNAS...81.6261P. doi:10.1073/pnas.81.20.6261. ISSN 0027-8424. PMC 391903. PMID 6436811.
- Ragsdale, S. W.; Wood, H. G. (10 April 1985). "Acetate biosynthesis by acetogenic bacteria. Evidence that carbon monoxide dehydrogenase is the condensing enzyme that catalyzes the final steps of the synthesis". The Journal of Biological Chemistry. 260 (7): 3970–3977. ISSN 0021-9258. PMID 2984190.
- STRAUSS, Gerhard; FUCHS, Georg (1993). "Enzymes of a novel autotrophic CO2 fixation pathway in the phototrophic bacterium Chloroflexus aurantiacus, the 3-hydroxypropionate cycle". European Journal of Biochemistry. 215 (3): 633–643. doi:10.1111/j.1432-1033.1993.tb18074.x. ISSN 0014-2956. PMID 8354269.
- Herter, S.; Busch, A.; Fuchs, G. (1 November 2002). "L-Malyl-Coenzyme A Lyase/ -Methylmalyl-Coenzyme A Lyase from Chloroflexus aurantiacus, a Bifunctional Enzyme Involved in Autotrophic CO2 Fixation". Journal of Bacteriology. 184 (21): 5999–6006. doi:10.1128/jb.184.21.5999-6006.2002. ISSN 0021-9193. PMC 135395. PMID 12374834.
- Berg, Ivan A. (7 January 2011). "Ecological Aspects of the Distribution of Different Autotrophic CO2Fixation Pathways". Applied and Environmental Microbiology. 77 (6): 1925–1936. doi:10.1128/aem.02473-10. ISSN 0099-2240. PMC 3067309. PMID 21216907.
- Zarzycki, Jan; Brecht, Volker; Müller, Michael; Fuchs, Georg (2 December 2009). "Identifying the missing steps of the autotrophic 3-hydroxypropionate CO2fixation cycle inChloroflexus aurantiacus". Proceedings of the National Academy of Sciences. 106 (50): 21317–21322. doi:10.1073/pnas.0908356106. ISSN 0027-8424. PMC 2795484. PMID 19955419.
- Berg IA, Kockelkorn D, Buckel W, Fuchs G (2007). "A 3-hydroxypropionate/4-hydroxybutyrate autotrophic carbon dioxide assimilation pathway in Archaea". Science. 318 (5857): 1782–6. Bibcode:2007Sci...318.1782B. doi:10.1126/science.1149976. PMID 18079405. S2CID 13218676.
- Huber H, Gallenberger M, Jahn U, Eylert E, Berg IA, Kockelkorn D, Eisenreich W, Fuchs G (2008). "A dicarboxylate/4-hydroxybutyrate autotrophic carbon assimilation cycle in the hyperthermophilic Archaeum Ignicoccus hospitalis". Proc. Natl. Acad. Sci. U.S.A. 105 (22): 7851–6. Bibcode:2008PNAS..105.7851H. doi:10.1073/pnas.0801043105. PMC 2409403. PMID 18511565.
- Encyclopedia of Microbiology. Academic Press. 2009. pp. 83–84. ISBN 9780123739445.
- Nicole Kresge; Robert D. Simoni; Robert L. Hill (2005). "The Discovery of Heterotrophic Carbon Dioxide Fixation by Harland G. Wood". The Journal of Biological Chemistry. 280 (18): e15.
- Adiredjo, Afifuddin Latif; Navaud, Olivier; Muños, Stephane; Langlade, Nicolas B.; Lamaze, Thierry; Grieu, Philippe; Bernacchi, Carl J. (3 July 2014). "Genetic Control of Water Use Efficiency and Leaf Carbon Isotope Discrimination in Sunflower (Helianthus annuus L.) Subjected to Two Drought Scenarios". PLOS ONE. 9 (7): e101218. Bibcode:2014PLoSO...9j1218A. doi:10.1371/journal.pone.0101218. PMC 4081578. PMID 24992022.
- Farquhar, G D; Ehleringer, J R; Hubick, K T (June 1989). "Carbon Isotope Discrimination and Photosynthesis". Annual Review of Plant Physiology and Plant Molecular Biology. 40 (1): 503–537. doi:10.1146/annurev.pp.40.060189.002443. S2CID 12988287.
- Seibt, Ulli; Rajabi, Abazar; Griffiths, Howard; Berry, Joseph A. (26 January 2008). "Carbon isotopes and water use efficiency: sense and sensitivity". Oecologia. 155 (3): 441–454. Bibcode:2008Oecol.155..441S. doi:10.1007/s00442-007-0932-7. PMID 18224341. S2CID 451126.
- Berg IA (2011). "Ecological aspects of the distribution of different autotrophic CO2 fixation pathways". Appl. Environ. Microbiol. 77 (6): 1925–36. doi:10.1128/AEM.02473-10. PMC 3067309. PMID 21216907.
Descent of plants and algaeEdit
- Keeling PJ (2004). "Diversity and evolutionary history of plastids and their hosts". Am. J. Bot. 91 (10): 1481–93. doi:10.3732/ajb.91.10.1481. PMID 21652304. S2CID 17522125.
- Keeling PJ (2009). "Chromalveolates and the evolution of plastids by secondary endosymbiosis" (PDF). J. Eukaryot. Microbiol. 56 (1): 1–8. doi:10.1111/j.1550-7408.2008.00371.x. PMID 19335769. S2CID 34259721. Archived from the original (PDF) on 9 July 2009. Retrieved 10 April 2012.
- Keeling PJ (2010). "The endosymbiotic origin, diversification and fate of plastids". Philos. Trans. R. Soc. Lond. B Biol. Sci. 365 (1541): 729–48. doi:10.1098/rstb.2009.0103. PMC 2817223. PMID 20124341.
- Timme RE, Bachvaroff TR, Delwiche CF (2012). "Broad phylogenomic sampling and the sister lineage of land plants". PLOS ONE. 7 (1): e29696. Bibcode:2012PLoSO...7E9696T. doi:10.1371/journal.pone.0029696. PMC 3258253. PMID 22253761.
- Spiegel FW (2012). "Evolution. Contemplating the first Plantae". Science. 335 (6070): 809–10. Bibcode:2012Sci...335..809S. doi:10.1126/science.1218515. PMID 22344435. S2CID 36584136.
- Price DC, Chan CX, Yoon HS, Yang EC, Qiu H, Weber AP, Schwacke R, Gross J, Blouin NA, Lane C, Reyes-Prieto A, Durnford DG, Neilson JA, Lang BF, Burger G, Steiner JM, Löffelhardt W, Meuser JE, Posewitz MC, Ball S, Arias MC, Henrissat B, Coutinho PM, Rensing SA, Symeonidi A, Doddapaneni H, Green BR, Rajah VD, Boore J, Bhattacharya D (2012). "Cyanophora paradoxa genome elucidates origin of photosynthesis in algae and plants" (PDF). Science. 335 (6070): 843–7. Bibcode:2012Sci...335..843P. doi:10.1126/science.1213561. PMID 22344442. S2CID 17190180. Archived from the original (PDF) on 14 May 2013. Retrieved 10 April 2012.