Photoautotrophs are organisms that can utilize light energy from sunlight and elements (such as carbon) from inorganic compounds to produce organic materials needed to sustain their own metabolism (i.e. autotrophy). Such biological activities are known as photosynthesis, and examples of such organisms include plants, algae and cyanobacteria.
Eukaryotic photoautotrophs absorb photonic energy through the photopigment chlorophyll (a porphyrin derivative) in their endosymbiont chloroplasts, while prokaryotic photoautotrophs use chlorophylls and bacteriochlorophylls present in free-floating cytoplasmic thylakoids or, in rare cases, membrane-bound retinal derivatives such as bacteriorhodopsin. The vast majority of known photoautotrophs perform photosynthesis that produce oxygen as a byproduct, while a small minority (such as haloarchaea and sulfur-reducing bacteria) perform anoxygenic photosynthesis.
Origin and the Great Oxidation Event
Chemical and geological evidence indicate that photosynthetic cyanobacteria existed about 2.6 billion years ago and anoxygenic photosynthesis had been taking place since a billion years before that. Oxygenic photosynthesis was the primary source of free oxygen and led to the Great Oxidation Event roughly 2.4 to 2.1 billion years ago during the Neoarchean-Paleoproterozoic boundary. Although the end of the Great Oxidation Event was marked by a significant decrease in gross primary productivity that eclipsed extinction events, the development of aerobic respiration enabled more energetic metabolism of organic molecules, leading to symbiogenesis and the evolution of eukaryotes, and allowing the diversification of complex life on Earth.
Prokaryotic photoautotrophs
Prokaryotic photoautotrophs include Cyanobacteria, Pseudomonadota, Chloroflexota, Acidobacteriota, Chlorobiota, Bacillota, Gemmatimonadota, and Eremiobacterota.
Cyanobacteria is the only prokaryotic group that performs oxygenic photosynthesis. Anoxygenic photosynthetic bacteria use PSI- and PSII-like photosystems, which are pigment protein complexes for capturing light. Both of these photosystems use bacteriochlorophyll. There are multiple hypotheses for how oxygenic photosynthesis evolved. The loss hypothesis states that PSI and PSII were present in anoxygenic ancestor cyanobacteria from which the different branches of anoxygenic bacteria evolved. The fusion hypothesis states that the photosystems merged later through horizontal gene transfer. The most recent hypothesis suggests that PSI and PSII diverged from an unknown common ancestor with a protein complex that was coded by one gene. These photosystems then specialized into the ones that are found today.
Eukaryotic photoautotrophs
Eukaryotic photoautotrophs include red algae, haptophytes, stramenopiles, cryptophytes, chlorophytes, and land plants. These organisms perform photosynthesis through organelles called chloroplasts and are believed to have originated about 2 billion years ago. Comparing the genes of chloroplast and cyanobacteria strongly suggests that chloroplasts evolved as a result of endosymbiosis with cyanobacteria that gradually lost the genes required to be free-living. However, it is difficult to determine whether all chloroplasts originated from a single, primary endosymbiotic event, or multiple independent events. Some brachiopods (Gigantoproductus) and bivalves (Tridacna) also evolved photoautotrophy.
References
- Olson, John M.; Blankenship, Robert E. (2004). "Thinking About the Evolution of Photosynthesis". Photosynthesis Research. 80 (1–3): 373–386. Bibcode:2004PhoRe..80..373O. doi:10.1023/B:PRES.0000030457.06495.83. ISSN 0166-8595. PMID 16328834. S2CID 1720483.
- Hodgskiss, Malcolm S. W.; Crockford, Peter W.; Peng, Yongbo; Wing, Boswell A.; Horner, Tristan J. (27 August 2019). "A productivity collapse to end Earth's Great Oxidation". Proceedings of the National Academy of Sciences. 116 (35): 17207–17212. Bibcode:2019PNAS..11617207H. doi:10.1073/pnas.1900325116. ISSN 0027-8424. PMC 6717284. PMID 31405980.
- Lyons, Timothy W.; Reinhard, Christopher T.; Planavsky, Noah J. (February 2014). "The rise of oxygen in Earth's early ocean and atmosphere". Nature. 506 (7488): 307–315. Bibcode:2014Natur.506..307L. doi:10.1038/nature13068. ISSN 0028-0836. PMID 24553238. S2CID 4443958.
- Sánchez-Baracaldo, Patricia; Cardona, Tanai (February 2020). "On the origin of oxygenic photosynthesis and Cyanobacteria". New Phytologist. 225 (4): 1440–1446. doi:10.1111/nph.16249. hdl:10044/1/74260. ISSN 0028-646X. PMID 31598981.
- Björn, Lars (June 2009). "The evolution of photosynthesis and chloroplasts". Current Science. 96 (11): 1466–1474.
- Yoon, Hwan Su; Hackett, Jeremiah D.; Ciniglia, Claudia; Pinto, Gabriele; Bhattacharya, Debashish (May 2004). "A Molecular Timeline for the Origin of Photosynthetic Eukaryotes". Molecular Biology and Evolution. 21 (5): 809–818. doi:10.1093/molbev/msh075. ISSN 1537-1719. PMID 14963099.
- George R. McGhee, Jr. (2019). Convergent Evolution on Earth. Lessons for the Search for Extraterrestrial Life. MIT Press. p. 47. ISBN 9780262354189. Retrieved 23 August 2022.
Photoautotrophs are organisms that can utilize light energy from sunlight and elements such as carbon from inorganic compounds to produce organic materials needed to sustain their own metabolism i e autotrophy Such biological activities are known as photosynthesis and examples of such organisms include plants algae and cyanobacteria Winogradsky column showing Photoautotrophs in purple and green Eukaryotic photoautotrophs absorb photonic energy through the photopigment chlorophyll a porphyrin derivative in their endosymbiont chloroplasts while prokaryotic photoautotrophs use chlorophylls and bacteriochlorophylls present in free floating cytoplasmic thylakoids or in rare cases membrane bound retinal derivatives such as bacteriorhodopsin The vast majority of known photoautotrophs perform photosynthesis that produce oxygen as a byproduct while a small minority such as haloarchaea and sulfur reducing bacteria perform anoxygenic photosynthesis Origin and the Great Oxidation EventChemical and geological evidence indicate that photosynthetic cyanobacteria existed about 2 6 billion years ago and anoxygenic photosynthesis had been taking place since a billion years before that Oxygenic photosynthesis was the primary source of free oxygen and led to the Great Oxidation Event roughly 2 4 to 2 1 billion years ago during the Neoarchean Paleoproterozoic boundary Although the end of the Great Oxidation Event was marked by a significant decrease in gross primary productivity that eclipsed extinction events the development of aerobic respiration enabled more energetic metabolism of organic molecules leading to symbiogenesis and the evolution of eukaryotes and allowing the diversification of complex life on Earth Prokaryotic photoautotrophsProkaryotic photoautotrophs include Cyanobacteria Pseudomonadota Chloroflexota Acidobacteriota Chlorobiota Bacillota Gemmatimonadota and Eremiobacterota Cyanobacteria is the only prokaryotic group that performs oxygenic photosynthesis Anoxygenic photosynthetic bacteria use PSI and PSII like photosystems which are pigment protein complexes for capturing light Both of these photosystems use bacteriochlorophyll There are multiple hypotheses for how oxygenic photosynthesis evolved The loss hypothesis states that PSI and PSII were present in anoxygenic ancestor cyanobacteria from which the different branches of anoxygenic bacteria evolved The fusion hypothesis states that the photosystems merged later through horizontal gene transfer The most recent hypothesis suggests that PSI and PSII diverged from an unknown common ancestor with a protein complex that was coded by one gene These photosystems then specialized into the ones that are found today Eukaryotic photoautotrophsEukaryotic photoautotrophs include red algae haptophytes stramenopiles cryptophytes chlorophytes and land plants These organisms perform photosynthesis through organelles called chloroplasts and are believed to have originated about 2 billion years ago Comparing the genes of chloroplast and cyanobacteria strongly suggests that chloroplasts evolved as a result of endosymbiosis with cyanobacteria that gradually lost the genes required to be free living However it is difficult to determine whether all chloroplasts originated from a single primary endosymbiotic event or multiple independent events Some brachiopods Gigantoproductus and bivalves Tridacna also evolved photoautotrophy ReferencesOlson John M Blankenship Robert E 2004 Thinking About the Evolution of Photosynthesis Photosynthesis Research 80 1 3 373 386 Bibcode 2004PhoRe 80 373O doi 10 1023 B PRES 0000030457 06495 83 ISSN 0166 8595 PMID 16328834 S2CID 1720483 Hodgskiss Malcolm S W Crockford Peter W Peng Yongbo Wing Boswell A Horner Tristan J 27 August 2019 A productivity collapse to end Earth s Great Oxidation Proceedings of the National Academy of Sciences 116 35 17207 17212 Bibcode 2019PNAS 11617207H doi 10 1073 pnas 1900325116 ISSN 0027 8424 PMC 6717284 PMID 31405980 Lyons Timothy W Reinhard Christopher T Planavsky Noah J February 2014 The rise of oxygen in Earth s early ocean and atmosphere Nature 506 7488 307 315 Bibcode 2014Natur 506 307L doi 10 1038 nature13068 ISSN 0028 0836 PMID 24553238 S2CID 4443958 Sanchez Baracaldo Patricia Cardona Tanai February 2020 On the origin of oxygenic photosynthesis and Cyanobacteria New Phytologist 225 4 1440 1446 doi 10 1111 nph 16249 hdl 10044 1 74260 ISSN 0028 646X PMID 31598981 Bjorn Lars June 2009 The evolution of photosynthesis and chloroplasts Current Science 96 11 1466 1474 Yoon Hwan Su Hackett Jeremiah D Ciniglia Claudia Pinto Gabriele Bhattacharya Debashish May 2004 A Molecular Timeline for the Origin of Photosynthetic Eukaryotes Molecular Biology and Evolution 21 5 809 818 doi 10 1093 molbev msh075 ISSN 1537 1719 PMID 14963099 George R McGhee Jr 2019 Convergent Evolution on Earth Lessons for the Search for Extraterrestrial Life MIT Press p 47 ISBN 9780262354189 Retrieved 23 August 2022
