Prochloron

Prochloron
Scientific classification Edit this classification
Domain: Bacteria
Kingdom: Bacillati
Phylum: Cyanobacteriota
Class: Cyanophyceae
Order: Synechococcales
Family: Prochloraceae
Genus: Prochloron
R.A.Lewin, 1977
Species
  • P. didemni (Lewin, 1977) = Synechocystis didemni[1]

Prochloron (from the Greek pro (before) and the Greek chloros (green) ) is a genus of unicellular oxygenic photosynthetic prokaryotes commonly found as an extracellular symbiont on coral reefs, particularly in didemnid ascidians (sea squirts). Part of the phylum cyanobacteria, it was theorized (endosymbiotic theory) that Prochloron is a predecessor of chloroplasts, components found in photosynthetic eukaryotic cells. However, this theory is largely refuted by phylogenetic studies which indicate Prochloron is not on the same line of descent that lead to the chloroplasts of algae and land plants.[2]

Prochloron was discovered in 1975 by Ralph A. Lewin of the Scripps Institution of Oceanography. Prochloron is one of three known prochlorophytes – cyanobacteria that contain both chlorophyll a and b bound to light-harvesting proteins.[2] The other prochlorophytes are Prochlorococcus marinus, an open-ocean species, and Prochlorothrix hollandica, a filamentous freshwater species. Surprisingly, unlike most cyanobacteria, Prochloron do not contain the red or blue pigments called phycobilins, seen in many species of cyanobacteria. Repeated unsuccessful attempts to culture Prochloron outside a host make them the only known obligate photosymbionts in the phylum Chordata.[3][4]

Strictly speaking, the name "Prochloron" Lewin 1977 was not validly published under either ICNP or ICNafp. The two codes do each have a valid version of the genus:

  • Prochloron Lewin 1977 ex Hoffmann and Greuter 1993, valid under ICNafp
  • Prochloron (ex Lewin 1977) Florenzano et al. 1986, valid under ICNP by being published in Int. J. Syst. Bacteriol.

Lewin originally placed Prochloron in a new family Prochloraceae, new order Prochlorales and a new algal division Prochlorophyta. In 1986, Florenzano et al. published Prochloraceae and Prochlorales under the bacterial code, within the class Photobacteria.[5] Komarek listed Prochlorococcus with Prochloron in Prochloraceae, and assigned the family to Synechococcales, but opined that the two genera are not closely related.[6]

LPSN, citing Strunecky et al. 2023 as source, places Prochloron in Microcystaceae[7], but this is a mistake because Strunecky et al. 2023 clearly place Prochloron in Prochloraceae.[8]

Species

The only taxonomically valid species is P. didemni. Again there is a version in each of the two Codes.

References

  1. ^ Kühl, Michael; Larkum, Anthony W.D. (2002). "The Microenvironment and Photosynthetic Performance of Prochloron sp. in Symbiosis with Didemnid Ascidians". In Seckbach, J. (ed.). Cellular origin and life in extreme habitats (PDF). Vol. 3: Symbiosis, mechanisms and model systems. Dordrecht: Kluwer Academic Publisheres. pp. 273–290.
  2. ^ a b La Roche, J.; van der Staay, G.W.M.; Ducret, A.; Aebersold, R.; Li, R.; Golden, S.S.; Hiller, R.G.; Wrench, P.M.; Larkum, A.W.D.; Green, B.R. (1996). "Independent evolution of the prochlorophyte and green plant chlorophyll a/b light-harvesting proteins". Proceedings of the National Academy of Sciences. 93 (26): 15244–48. Bibcode:1996PNAS...9315244L. doi:10.1073/pnas.93.26.15244. PMC 26388. PMID 8986795.
  3. ^ Withers, NW; Alberte, RS; Lewin, RA; Thornder, JP; Britton, G; Goodwin, TW (May 1978). "Photosynthetic unit size, carotenoids, and chlorophyll-protein composition of Prochloron sp., a prokaryotic green alga". Proceedings of the National Academy of Sciences. 75 (5): 2301–2305. Bibcode:1978PNAS...75.2301W. doi:10.1073/pnas.75.5.2301. PMC 392540. PMID 16592528.
  4. ^ Kuhl, M; Behrendt, L; Trampe, E.; Qvortrup, K; Schreiber, U; Borisov, S.; Larkum, A (November 2012). "Microenvironmental Ecology of the chlorophyll b-containing Symbiotic Cyanabacterium Prochloron in the Didemnid Ascidian Lissoclinum patella". Frontiers in Microbiology. 3: 402. doi:10.3389/fmicb.2012.00402. PMC 3510431. PMID 23226144.
  5. ^ Florenzano, Gino; Balloni, Waldemaro; Materassi, Riccardo (1986). "Nomenclature of Prochloron didemni (Lewin 1977) sp. nov., nom. rev., Prochloron (Lewin 1976) gen. nov., nom. rev., Prochloraceae fam. nov., Prochlorales ord. nov., nom. rev. in the class Photobacteria Gibbons and Murray 1978". International Journal of Systematic and Evolutionary Microbiology. 36 (2): 351–353. doi:10.1099/00207713-36-2-351. ISSN 1466-5034.
  6. ^ J, Komárek; J, Kaštovský; R, Mareš J. & Johansen J. "Taxonomic classification of cyanoprokaryotes (cyanobacterial genera) 2014, using a polyphasic approach". Preslia. 86 (4). ISSN 0032-7786.
  7. ^ "Family: Prochloraceae". lpsn.dsmz.de. Retrieved 2025-10-09.
  8. ^ Strunecky, Otakar & Ivanova, Anna & Mares, Jan. (2023). An updated classification of cyanobacterial orders and families based on phylogenomic and polyphasic analysis. [1]


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