Prochlorococcus

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Prochlorococcus
Scientific classification
Kingdom: Bacteria
Phylum: Cyanobacteria
Order: Synechococcales
Family: Synechococcaceae
Genus: Prochlorococcus
Chisholm et al., 1992
Species

P. marinus

Prochlorococcus is a genus of very small (0.6 µm) marine cyanobacteria with an unusual pigmentation (chlorophyll b). These bacteria belong to the photosynthetic picoplankton and are probably the most abundant photosynthetic organism on Earth. Microbes of the genus Prochlorococcus are among the major primary producers in the ocean, responsible for at least 50% of atmospheric oxygen.[1] Analysis of the genome sequences of 12 Prochlorococcus strains show that 1100 genes are common to all strains, and the average genome size is about 2000 genes.[1] In contrast, eukaryotic algae have over 10,000 genes.[2]

Discovery[edit]

Although there had been several earlier records of very small chlorophyll-b-containing cyanobacteria in the ocean,[3][4] Prochlorococcus was discovered in 1986[5] by Sallie W. (Penny) Chisholm of the Massachusetts Institute of Technology, Robert J. Olson of the Woods Hole Oceanographic Institution, and other collaborators in the Sargasso Sea using flow cytometry. The first culture of Prochlorococcus was isolated in the Sargasso Sea in 1988 (strain SS120) and shortly another strain was obtained from the Mediterranean Sea (strain MED). The name Prochlorococcus[6] originated from the fact it was originally assumed that Prochlorococcus was related to Prochloron and other chlorophyll-b-containing bacteria, called prochlorophytes, but it is now known that prochlorophytes form several separate phylogenetic groups within the cyanobacteria subgroup of the bacteria kingdom.

The only species of the genus that has been described is Prochlorococcus marinus.

Morphology[edit]

Marine cyanobacteria are to date the smallest known photosynthetic organisms; Prochlorococcus is the smallest at just 0.5 to 0.8 micrometres across. The coccoid shaped cells are non-motile and free-living. Their small size, and therefore large surface-to-volume ratio, gives them an advantage in nutrient poor water. Still, it is assumed that Prochlorococcus have a very small nutrient requirement.[7] Typically, Prochlorococcus divide once a day in the subsurface layer or oligotrophic waters.[7]

Distribution[edit]

Prochlorococcus has been found to be abundant in the euphotic zone of the world's tropical oceans.[8] It is possibly the most plentiful species on Earth: a single millilitre of surface seawater may contain 100,000 cells or more. Worldwide, the average yearly abundance is between 2.8 and 3.0 octillion (~1027) individuals[9] (for comparison, that is approximately the number of atoms in a ton of gold). Prochlorococcus is ubiquitous between 40°N and 40°S and dominates in the oligotrophic (nutrient poor) regions of the oceans.[10] Prochlorococcus is mostly found in a temperature range of 10-33 °C and some strains can grow at depths with low light (<1% surface light).[1] The bacterium accounts for an estimated 20% of the oxygen in the Earth's atmosphere, and forms part of the base of the ocean food chain.[11]

Pigments[edit]

Prochlorococcus is closely related to Synechococcus, another abundant photosynthetic cyanobacteria, which contains the light-harvesting antennae phycobilisomes. However, Prochlorochoccus has evolved to use a unique light-harvesting complex, consisting predominantly of divinyl derivatives of chlorophyll a (Chl a2) and b (Chl b2) and lacking monovinyl chlorophylls and phycobilisomes.[12] Prochlorococcus is the only known wild-type oxygenic phototroph that does not contain Chl a as a major photosynthetic pigment, and is the only known prokaryote with α-carotene.[13]

Prochlorococcus occupies two distinct niches, leading to the nomenclature of the low light (LL) and high light (HL) groups,[14] which vary in pigment ratios (LL has a high ratio of chlorophyll b2:a2 and HL has a low ratio of b2:a2), light requirements, nitrogen and phosphorus utilization, copper and virus sensitivity. These "ecotypes" can be differentiated on the basis of the sequence of their ribosomal RNA gene. High-light adapted strains inhabit depths between 25 and 100 m, while low-light adapted strains inhabit waters between 80 and 200 m.[15] Recently the genomes of several strains of Prochlorococcus have been sequenced.[16][17] Twelve complete genomes have been sequenced which reveal physioloically and genetically distinct lineages of Prochlorococcus marinus that are 97% similar in the 16S rRNA gene.[15]

See also[edit]

References[edit]

  1. ^ a b c Munn, C. Marine Microbiology: ecology and applications Second Ed. Garland Science, 2011.
  2. ^ Kettler GC, Martiny AC, Huang K, et al. (December 2007). "Patterns and Implications of Gene Gain and Loss in the Evolution of Prochlorococcus". PLoS Genetics 3 (12): e231. doi:10.1371/journal.pgen.0030231. PMC 2151091. PMID 18159947. 
  3. ^ P. W. Johnson & J. M. Sieburth (1979). "Chroococcoid cyanobacteria in the sea: a ubiquitous and diverse phototrophic biomass". Limnology and Oceanography 24 (5): 928–935. doi:10.4319/lo.1979.24.5.0928. 
  4. ^ W. W. C. Gieskes & G. W. Kraay (1983). "Unknown chlorophyll a derivatives in the North Sea and the tropical Atlantic Ocean revealed by HPLC analysis". Limnology and Oceanography 28 (4): 757–766. doi:10.4319/lo.1983.28.4.0757. 
  5. ^ S. W. Chisholm, R. J. Olson, E. R. Zettler, J. Waterbury, R. Goericke & N. Welschmeyer (1988). "A novel free-living prochlorophyte occurs at high cell concentrations in the oceanic euphotic zone". Nature 334 (6180): 340–343. doi:10.1038/334340a0. 
  6. ^ Sallie W. Chisholm, S. L. Frankel, R. Goericke, R. J. Olson, B. Palenik, J. B. Waterbury, L. West-Johnsrud & E. R. Zettler (1992). "Prochlorococcus marinus nov. gen. nov. sp.: an oxyphototrophic marine prokaryote containing divinyl chlorophyll a and b". Archives of Microbiology 157 (3): 297–300. doi:10.1007/BF00245165. 
  7. ^ a b Partensky F, Hess WR, Vaulot D (1999). "Prochlorococcu, a marine photosynthetic prokaryote of global significance.". Microbiology and Molecular Biology Reviews 63 (1): 106–127. 
  8. ^ Chisholm, S.W., S. Frankel, R. Goericke, R. Olson, B. Palenik, J. Waterbury, L. West-Johnsrud, and E. Zettler. (1992). Prochlorococcus marinus nov. gen. nov. sp.: an oxyphototrophic marine prokaryote containing divinyl chlorophyll a and b. Archives of Microbiology, 157(3), 297-300.
  9. ^ Flombaum, P.; Gallegos, J. L.; Gordillo, R. A.; Rincon, J.; Zabala, L. L.; Jiao, N.; Karl, D. M.; Li, W. K. W.; Lomas, M. W.; Veneziano, D.; Vera, C. S.; Vrugt, J. A.; Martiny, A. C. (2013). "Present and future global distributions of the marine Cyanobacteria Prochlorococcus and Synechococcus". Proceedings of the National Academy of Sciences 110 (24): 9824. doi:10.1073/pnas.1307701110.  edit
  10. ^ F. Partensky, W. R. Hess & D. Vaulot (1999). "Prochlorococcus, a Marine Photosynthetic Prokaryote of Global Significance". Microbiology and Molecular Biology Reviews 63 (1): 106–127. PMC 98958. PMID 10066832. 
  11. ^ The Most Important Microbe You've Never Heard Of
  12. ^ Ting CS, Rocap G, King J, and Chisholm S (2002). "Cyanobacterial photosynthesis in the oceans: the origins and significance of divergent light-harvesting strategies". Trends in Microbiology 10 (3): 134–142. 
  13. ^ Goericke R and Repeta D (1992). "The pigments of Prochlorococcus marinus: the presence of divinyl chlorophyll a and b in a marine prokaryote". Limnology and Oceanography 37 (2): 425–433. 
  14. ^ N. J. West & D. J. Scanlan (1999). "Niche-partitioning of Prochlorococcus in a stratified water column in the eastern North Atlantic Ocean". Applied and Environmental Microbiology 65: 2585–2591. 
  15. ^ a b Martiny AC, Tai A, Veneziano D, Primeau F, Chisholm S (2009). "Taxonomic resolution, ecotypes and biogeography of Prochlorococcus". Environmental Microbiology 11 (4): 823–832. doi:10.1111/j.1462-2920.2008.01803.x. 
  16. ^ G. Rocap, F. W. Larimer, J. Lamerdin, S. Malfatti, P. Chain, N. A. Ahlgren, A. Arellano, M. Coleman, L. Hauser, W. R. Hess, Z. I. Johnson, M. Land, D. Lindell, A. F. Post, W. Regala, M. Shah, S. L. Shaw, C. Steglich, M. B. Sullivan, C. S. Ting, A. Tolonen, E. A. Webb, E. R. Zinser & S. W. Chisholm (2003). "Genome divergence in two Prochlorococcus ecotypes reflects oceanic niche differentiation" (– Scholar search). Nature 424 (6952): 1042–1047. doi:10.1038/nature01947. PMID 12917642. [dead link]
  17. ^ A. Dufresne, M. Salanoubat, F. Partensky, F. Artiguenave, I. M. Axmann, V. Barbe, S. Duprat, M. Y. Galperin, E. V. Koonin, F. Le Gall, K. S. Makarova, M. Ostrowski, S. Oztas, C. Robert, I. B. Rogozin, D. J. Scanlan, N. Tandeau de Marsac, J. Weissenbach, P. Wincker, Y. I. Wolf & W. R. Hess (2003). "Genome sequence of the cyanobacterium Prochlorococcus marinus SS120, a nearly minimal oxyphototrophic genome". Proceedings of the National Academy of Sciences 100 (17): 10020–10025. doi:10.1073/pnas.1733211100. PMC 187748. PMID 12917486. 

Further reading[edit]

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