Editing Prochlorococcus

{{Short description|Genus of bacteria}}{{Italic title}}{{Speciesbox
| image = Prochlorococcus marinus.jpg
| image_alt = SEM of ''Prochlorococcus marinus'' pseudo-colored
| image_caption = [[Transmission electron microscope|TEM]] image of ''Prochlorococcus marinus'' ([[pseudo-colored]])
| image2 =
| image2_alt =
| image2_caption =
| genus = Prochlorococcus
| parent_authority = [[Sallie W. Chisholm|Chisholm]] et al., 1992
| species = marinus
| authority = Chisholm et al., 1992
}}

'''''Prochlorococcus''''' is a [[genus]] of very small (0.6&nbsp;[[micrometre|μm]]) [[Ocean|marine]] [[cyanobacteria]] with an unusual pigmentation ([[Chlorophyll|chlorophyll ''a2'' and ''b2'']]). These bacteria belong to the [[photosynthetic picoplankton]] and are probably the most abundant [[photosynthesis|photosynthetic]] organism on Earth. ''Prochlorococcus'' microbes are among the major [[primary producers]] in the ocean, responsible for a large percentage of the photosynthetic production of [[oxygen]].<ref name="Munn">{{ cite book |last=Munn|first= C.  |title=Marine Microbiology: Ecology and applications|edition=2nd |publisher=Garland Science|date= 2011}}{{pn |date=January 2024}}</ref><ref name="www.hup.harvard.edu">{{Cite book|url=http://www.hup.harvard.edu/catalog.php?isbn=9780674975910|title=Life at the Edge of Sight |first1= Scott|last1= Chimileski|first2= Roberto|last2= Kolter |date=25 September 2017 |publisher=Belknap Press |isbn=978-0-674-97591-0 |language=en|access-date=2018-01-26}}{{pn|date=January 2024}}</ref> ''Prochlorococcus'' strains, called ecotypes, have physiological differences enabling them to exploit different ecological niches.<ref>{{cite journal | pmid = 17016519 | doi=10.1038/msb4100087 | volume=2 | issue=1 | title=Global gene expression of ''Prochlorococcus'' ecotypes in response to changes in nitrogen availability | pmc=1682016 |date=October 2006 | at=53  |vauthors=Tolonen AC, Aach J, Lindell D, Johnson ZI, Rector T, Steen R, Church GM, Chisholm SW | journal = Molecular Systems Biology |doi-access=free}} </ref> Analysis of the [[Genome|genome sequences]] of ''Prochlorococcus'' strains show that 1,273<ref name="Kettler-2007" /> genes are common to all strains, and the average genome size is about 2,000 [[gene]]s.<ref name="Munn"/> In contrast, [[Eukaryote|eukaryotic]] [[algae]] have over 10,000 genes.<ref name="Kettler-2007">{{cite journal | pmid = 18159947 | doi=10.1371/journal.pgen.0030231 | volume=3 | issue=12 | title=Patterns and Implications of Gene Gain and Loss in the Evolution of ''Prochlorococcus'' | pmc=2151091 |date=December 2007 | at=e231  |vauthors=Kettler GC, Martiny AC, Huang K, etal | journal = <!-- Citation bot no --> PLoS Genetics | doi-access=free }}</ref>

The genus and the type species were made [[validly published names]] under the [[ICNP]] in 2001 with ''Validation list no. 79''.<ref>{{cite journal |title=Validation of publication of new names and new combinations previously effectively published outside the IJSEM. |journal=International Journal of Systematic and Evolutionary Microbiology |date=1 March 2001 |volume=51 |issue=2 |pages=263–265 |doi=10.1099/00207713-51-2-263}}</ref> They became valid under the [[ICNafp]] in 2020 with the description of Komárek et al.<ref>{{cite journal |last1=Komárek |first1=Jiří |last2=Johansen |first2=Jeffrey R. |last3=Šmarda |first3=Jan |last4=Strunecký |first4=Otakar |title=Phylogeny and taxonomy of Synechococcus-like cyanobacteria |journal=Fottea |date=14 October 2020 |volume=20 |issue=2 |pages=171–191 |doi=10.5507/fot.2020.006}}</ref>

==Discovery==
Although there had been several earlier records of very small chlorophyll-''b''-containing cyanobacteria in the ocean,<ref>{{cite journal |doi=10.4319/lo.1979.24.5.0928 |first1=P.W. |last1=Johnson |author2-link=John McNeill Sieburth |first2=J.M. |last2=Sieburth |year=1979 |title=Chroococcoid cyanobacteria in the sea: a ubiquitous and diverse phototrophic biomass |journal=Limnology and Oceanography |volume=24 |pages=928–935 |issue=5|bibcode=1979LimOc..24..928J }}</ref><ref>{{cite journal |doi=10.4319/lo.1983.28.4.0757 |first1=W.W.C. |last1=Gieskes |first2=G.W. |last2=Kraay  |year=1983 |title=Unknown chlorophyll ''a'' derivatives in the North Sea and the tropical Atlantic Ocean revealed by HPLC analysis |journal=Limnology and Oceanography |volume=28 |pages=757–766 |issue=4|bibcode=1983LimOc..28..757G |doi-access=free }}</ref> ''Prochlorococcus'' was discovered in 1986<ref>{{cite journal |first1=S.W. |last1=Chisholm |first2=R.J. |last2=Olson |first3=E.R. |last3=Zettler |first4=J. |last4=Waterbury |first5=R. |last5=Goericke |first6=N. |last6=Welschmeyer |year=1988 |title=A novel free-living prochlorophyte occurs at high cell concentrations in the oceanic euphotic zone |journal=[[Nature (journal)|Nature]] |volume=334 |pages=340–3 |doi=10.1038/334340a0 |issue=6180 |bibcode=1988Natur.334..340C|s2cid=4373102 }}</ref> by [[Sallie W. Chisholm|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]]. Chisholm was awarded the [[Crafoord Prize]] in 2019 for the discovery.<ref>{{cite web |title=The Crafoord Prize in Biosciences 2019|url=https://www.crafoordprize.se/press_release/the-crafoord-prize-in-biosciences-2019|publisher=Royal Swedish Academy of Sciences|date=January 17, 2019|access-date=April 26, 2022}}</ref> The first culture of ''Prochlorococcus'' was isolated in the Sargasso Sea in 1988 ([[strain (biology)|strain]] SS120) and shortly another strain was obtained from the [[Mediterranean Sea]] (strain MED). The name ''Prochlorococcus''<ref>{{cite journal |author-link1=Sallie W. Chisholm |first1=S.W. |last1=Chisholm |first2=S.L. |last2=Frankel |first3=R. |last3=Goericke |first4=R.J. |last4=Olson |first5=B. |last5=Palenik |first6=J.B. |last6=Waterbury |first7=L. |last7=West-Johnsrud |first8=E.R. |last8=Zettler |year=1992 |title=''Prochlorococcus marinus'' nov. gen. nov. sp.: an oxyphototrophic marine prokaryote containing divinyl chlorophyll a and b |journal=Archives of Microbiology |volume=157 |pages=297–300 |doi=10.1007/BF00245165 |issue=3|bibcode=1992ArMic.157..297C |s2cid=32682912 }}</ref> 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 tree|phylogenetic]] groups within the cyanobacteria subgroup of the [[bacteria]] domain. The only species within the genus described is ''Prochlorococcus marinus'', although two subspecies have been named for low-light and high-light adapted niche variations.<ref name="NCBI">{{Cite web |title=''Prochlorococcus marinus'' |url=https://www.ncbi.nlm.nih.gov/data-hub/taxonomy/1219/ |access-date=2022-04-25 |website=NCBI |language=en}}</ref>

==Morphology==
Marine cyanobacteria are to date the smallest known [[Photosynthesis|photosynthetic]] organisms; ''Prochlorococcus'' is the smallest at just 0.5 to 0.7 micrometres in diameter.<ref name="Biller-2014">{{cite journal|last1=Biller|first1=Steven J.|last2=Berube|first2=Paul M.|last3=Lindell|first3=Debbie|author-link3=Debbie Lindell|last4=Chisholm|first4=Sallie W.|title=Prochlorococcus: the structure and function of collective diversity|journal=Nature Reviews Microbiology|date=1 December 2014|volume=13|issue=1|pages=13–27|doi=10.1038/nrmicro3378|pmid=25435307|url=https://dspace.mit.edu/bitstream/1721.1/97151/2/NRM_final_wfigs%20for%20Dspace.pdf|hdl=1721.1/97151|s2cid=18963108|hdl-access=free}}</ref><ref name="www.hup.harvard.edu" /> The coccoid shaped cells are non-motile and free-living. Their small size and large [[surface-area-to-volume ratio]], gives them an advantage in nutrient-poor water. Still, it is assumed that ''Prochlorococcus'' have a very small nutrient requirement.<ref name="Partensky">{{cite journal | url= | volume=63 | issue=1 | title=''Prochlorococcus'', a marine photosynthetic prokaryote of global significance | year=1999 | pages=106–127 |vauthors=Partensky F, Hess WR, Vaulot D | journal=Microbiology and Molecular Biology Reviews | pmid = 10066832 | pmc=98958| doi=10.1128/MMBR.63.1.106-127.1999 }}</ref> Moreover, ''Prochlorococcus'' have adapted to use [[sulfolipids]] instead of phospholipids in their membranes to survive in phosphate deprived environments.<ref name="Sulfolipid">{{cite journal|last1=Van Mooy|first1=B. A. S.|last2=Rocap|first2=G.|last3=Fredricks|first3=H. F.|last4=Evans|first4=C. T.|last5=Devol|first5=A. H.|title=Sulfolipids dramatically decrease phosphorus demand by picocyanobacteria in oligotrophic marine environments|journal=Proceedings of the National Academy of Sciences|date=26 May 2006|volume=103|issue=23|pages=8607–12|doi=10.1073/pnas.0600540103|pmid=16731626|pmc=1482627|bibcode=2006PNAS..103.8607V|doi-access=free}}</ref> This adaptation allows them to avoid competition with heterotrophs that are dependent on phosphate for survival.<ref name="Sulfolipid" /> Typically, ''Prochlorococcus'' divide once a day in the subsurface layer or oligotrophic waters.<ref name="Partensky"/>

==Distribution==
''Prochlorococcus'' is abundant in the [[Photic zone|euphotic]] zone of the world's tropical oceans.<ref>{{cite journal | last1 = Chisholm | first1 = S.W. | last2 = Frankel | first2 = S. | last3 = Goericke | first3 = R. | last4 = Olson | first4 = R. | last5 = Palenik | first5 = B. | last6 = Waterbury | first6 = J. | last7 = West-Johnsrud | first7 = L. | last8 = Zettler | first8 = E. | year = 1992 | title = ''Prochlorococcus marinus'' nov. gen. nov. sp.: an oxyphototrophic marine prokaryote containing divinyl chlorophyll a and b. | journal = Archives of Microbiology | volume = 157 | issue = 3| pages = 297–300 | doi=10.1007/bf00245165| bibcode = 1992ArMic.157..297C | s2cid = 32682912 }}</ref> It is possibly the most plentiful genus on Earth: a single millilitre of surface seawater may contain 100,000 cells or more. Worldwide, the average yearly abundance is {{val|2.8|to|3.0|e=27}} individuals<ref name=Flombaum13>{{Cite journal | last1 = Flombaum | first1 = P. | last2 = Gallegos | first2 = J. L. | last3 = Gordillo | first3 = R. A. | last4 = Rincon | first4 = J. | last5 = Zabala | first5 = L. L. | last6 = Jiao | first6 = N. | last7 = Karl | first7 = D. M. | last8 = Li | first8 = W. K. W. | last9 = Lomas | first9 = M. W. | doi = 10.1073/pnas.1307701110 | last10 = Veneziano | first10 = D. | last11 = Vera | first11 = C. S. | last12 = Vrugt | first12 = J. A. | last13 = Martiny | first13 = A. C. | title = Present and future global distributions of the marine Cyanobacteria ''Prochlorococcus'' and ''Synechococcus'' | journal = Proceedings of the National Academy of Sciences | volume = 110 | issue = 24 | pages = 9824–9 | year = 2013 | pmid =  23703908| pmc = 3683724| bibcode = 2013PNAS..110.9824F | doi-access = free }}</ref> (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 [[oligotroph]]ic (nutrient-poor) regions of the oceans.<ref name="Partensky" />  ''Prochlorococcus'' is mostly found in a temperature range of 10–33&nbsp;°C and some strains can grow at depths with low light (<1% surface light).<ref name="Munn"/> These strains are known as LL (Low Light) ecotypes, with strains that occupy shallower depths in the water column known as HL (High Light) ecotypes.<ref>{{cite journal | last1 = Coleman | first1 = M. | last2 = Sullivan | first2 = M. | last3 = Martiny | first3 = A. | last4 = Steglich | first4 = C. | last5 = Barry | first5 = K. | last6 = DeLong | first6 = E. | last7 = Chisholm | first7 = S. | year = 2006 | title = Genomic islands and the ecology and evolution of ''Prochlorococcus'' | url = http://www.escholarship.org/uc/item/6506g5sk| journal = Science | volume = 311 | issue = 5768| pages = 1768–70 | doi=10.1126/science.1122050 | pmid=16556843| bibcode = 2006Sci...311.1768C | s2cid = 3196592 | url-access = subscription }}</ref> Furthermore, ''Prochlorococcus'' are more plentiful in the presence of heterotrophs that have catalase abilities.<ref name="ROS">{{cite journal|last1=Morris|first1=J. J.|last2=Kirkegaard|first2=R.|last3=Szul|first3=M. J.|last4=Johnson|first4=Z. I.|last5=Zinser|first5=E. R.|title=Facilitation of Robust Growth of ''Prochlorococcus'' Colonies and Dilute Liquid Cultures by "Helper" Heterotrophic Bacteria|journal=Applied and Environmental Microbiology|date=23 May 2008|volume=74|issue=14|pages=4530–4|doi=10.1128/AEM.02479-07|pmid=18502916|pmc=2493173|bibcode=2008ApEnM..74.4530M}}</ref> ''Prochlorococcus'' do not have mechanisms to degrade reactive oxygen species and rely on heterotrophs to protect them.<ref name="ROS" /> The bacterium accounts for an estimated 13–48% of the global photosynthetic production of [[oxygen]], and forms part of the base of the ocean [[food chain]].<ref name="Niche Partitioning">{{cite journal|last1=Johnson|first1=Zachary I.|last2=Zinser|first2=Erik R.|last3=Coe|first3=Allison|last4=McNulty|first4=Nathan P.|last5=Woodward|first5=E. Malcolm S.|last6=Chisholm|first6=Sallie W.|title=Niche Partitioning among ''Prochlorococcus'' Ecotypes along Ocean-Scale Environmental Gradients|journal=Science|date=2006|volume=311|issue=5768|pages=1737–40|doi=10.1126/science.1118052|pmid=16556835|bibcode=2006Sci...311.1737J|s2cid=3549275}}</ref>

==Pigments==
''Prochlorococcus'' is closely related to ''[[Synechococcus]],'' another abundant photosynthetic cyanobacteria, which contains the light-harvesting antennae [[Phycobilisome|phycobilisomes]]. However, ''Prochlorochoccus'' has evolved to use a unique light-harvesting complex, consisting predominantly of divinyl derivatives of [[chlorophyll a]] (Chl a2) and [[chlorophyll b]] (Chl b2) and lacking monovinyl chlorophylls and phycobilisomes.<ref>{{cite journal |vauthors=Ting CS, Rocap G, King J, Chisholm S |year=2002 |title=Cyanobacterial photosynthesis in the oceans: the origins and significance of divergent light-harvesting strategies |journal=[[Trends in Microbiology]] |volume=10 |issue=3 |pages=134–142 |doi=10.1016/s0966-842x(02)02319-3|pmid=11864823 }}</ref> ''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.<ref>{{cite journal |vauthors=Goericke R, Repeta D|year=1992 |title=The pigments of ''Prochlorococcus marinus'': the presence of divinyl chlorophyll a and b in a marine prokaryote |journal=[[Limnology and Oceanography]] |volume=37 |issue=2 |pages=425–433 |doi=10.4319/lo.1992.37.2.0425|bibcode=1992LimOc..37..425R |doi-access=free }}</ref>

==Genome==
The genomes of several strains of ''Prochlorococcus'' have been sequenced.<ref name=Rocap03>{{cite journal|first1=G. |last1=G. Rocap |first2=F.W. |last2=Larimer |first3=J. |last3=Lamerdin |first4=S. |last4=Malfatti |first5=P. |last5=Chain |first6=N.A. |last6=Ahlgren |first7=A. |last7=Arellano |first8=M. |last8=Coleman |first9=L. |last9=Hauser |first10=W.R. |last10=Hess |first11=Z.I. |last11=Johnson |first12=M. |last12=Land |first13=D. |last13=Lindell |author-link13=Debbie Lindell |first14=A.F. |last14=Post |first15=W. |last15=Regala |first16=M. |last16=Shah |first17=S.L. |last17=Shaw |first18=C. |last18=Steglich |first19=M.B. |last19=Sullivan |first20=C.S. |last20=Ting |first21=A. |last21=Tolonen |first22=E.A. |last22=Webb |first23=E.R. |last23=Zinser |first24=S.W. |last24=Chisholm |year=2003 |title=Genome divergence in two ''Prochlorococcus'' ecotypes reflects oceanic niche differentiation |journal=[[Nature (journal)|Nature]] |volume=424 |pmid=12917642 |issue=6952 |pages=1042–7 |doi=10.1038/nature01947 |url=https://www.nature.com/articles/nature01947 |bibcode=2003Natur.424.1042R |s2cid=4344597 }}</ref><ref name=Dufresne03/> Twelve complete genomes have been sequenced which reveal physiologically and genetically distinct lineages of ''Prochlorococcus marinus'' that are 97% similar in the 16S rRNA gene.<ref name="Martiny">{{cite journal|vauthors=Martiny AC, Tai A, Veneziano D, Primeau F, Chisholm S|year=2009|title=Taxonomic resolution, ecotypes and biogeography of ''Prochlorococcus''|journal=[[Environmental Microbiology]]|volume=11|issue=4|pages=823–832|doi=10.1111/j.1462-2920.2008.01803.x|pmid=19021692|bibcode=2009EnvMi..11..823M |s2cid=25323390 |url=https://www.escholarship.org/uc/item/2c3638zx |url-access=subscription}}</ref> Research has shown that a massive genome reduction occurred during the Neoproterozoic [[Snowball Earth]], which was followed by [[population bottleneck]]s.<ref>{{cite journal | pmc=10837832 | date=2024 | last1=Zhang | first1=H. | last2=Hellweger | first2=F. L. | last3=Luo | first3=H. | title=Genome reduction occurred in early ''Prochlorococcus'' with an unusually low effective population size | journal=The ISME Journal | volume=18 | issue=1 | pages=wrad035 | doi=10.1093/ismejo/wrad035 | pmid=38365237 }}</ref>

The high-light ecotype has the smallest genome (1,657,990 basepairs, 1,716 genes) of any known oxygenic phototroph, but the genome of the low-light type is much larger (2,410,873 base pairs, 2,275 genes).<ref name=Rocap03/>

==DNA recombination, repair and replication==

Marine ''Prochlorococcus'' [[cyanobacteria]] have several genes that function in DNA [[homologous recombination|recombination]],  [[DNA repair|repair]] and [[DNA replication|replication]].  These include the ''[[recBCD]]'' gene complex whose product, [[exonuclease]] V, functions in recombinational repair of DNA, and the ''umuCD'' gene complex whose product, [[DNA polymerase V]], functions in error-prone DNA replication.<ref name = Cassier-Chauvat2016>{{cite journal |vauthors=Cassier-Chauvat C, Veaudor T, Chauvat F |title=Comparative Genomics of DNA Recombination and Repair in Cyanobacteria: Biotechnological Implications |journal=Front Microbiol |volume=7 |pages=1809 |date=2016 |pmid=27881980 |pmc=5101192 |doi=10.3389/fmicb.2016.01809 |doi-access=free}}</ref> These cyanobacteria also have the gene ''lexA'' that regulates an [[SOS response]] system, probably a system like the well-studied ''E. coli'' SOS system that is employed in the response to [[DNA damage (naturally occurring)|DNA damage]].<ref name = Cassier-Chauvat2016/>

==Ecology==
Ancestors of ''Prochlorococcus'' contributed to the production of early atmospheric oxygen.<ref>{{Citation |title=The tiny creature that secretly powers the planet {{!}} Penny Chisholm | date=23 July 2018 |url=https://www.youtube.com/watch?v=ylOlZz7s52Q |language=en |access-date=2022-04-26}}</ref> Despite ''Prochlorococcus'' being one of the smallest types of marine phytoplankton in the world's oceans, its substantial number make it responsible for a major part of the oceans', world's photosynthesis, and oxygen production.<ref name="www.hup.harvard.edu" /> The size of ''Prochlorococcus'' (0.5 to 0.7&nbsp;μm)<ref name="Partensky" /> and the adaptations of the various ecotypes allow the organism to grow abundantly in low nutrient waters such as the waters of the tropics and the subtropics (c. 40°N to 40°S);<ref>{{cite journal |last1=Partensky |first1=F.  |last2=Blanchot  |first2=J. |last3=Vaulot |first3=D. |title=Differential distribution and ecology of ''Prochlorococcus'' and ''Synechococcus'' in oceanic waters: a review|journal=Bulletin de l'Institut Océanographique de Monaco |date=1999 |issue=spécial 19 |page=431 |issn=0304-5722}}</ref> however, they can be found in higher latitudes as high up as 60° north but at fairly minimal concentrations and the bacteria's distribution across the oceans suggest that the colder waters could be fatal. This wide range of latitude along with the bacteria's ability to survive up to depths of 100 to 150&nbsp;metres, i.e. the average depth of the mixing layer of the surface ocean, allows it to grow to enormous numbers, up to {{Val|3|e=27}} individuals worldwide.<ref name=Flombaum13 /> This enormous number makes the ''Prochlorococcus'' play an important role in the global [[carbon cycle]] and oxygen production. Along with ''[[Synechococcus]]'' (another genus of cyanobacteria that co-occurs with ''Prochlorococcus'') these cyanobacteria are responsible for approximately 50% of marine carbon fixation, making it an important [[carbon sink]] via the biological carbon pump (i.e. the transfer of organic carbon from the surface ocean to the deep via several biological, physical and chemical processes).<ref>{{cite journal|first1=Fei-Xue|last1=Fu|first2=Mark E.|last2=Warner|first3=Yaohong|last3=Zhang|first4=Yuanyuan|last4=Feng|first5=David A.|last5=Hutchins|title=Effects of Increased Temperature and CO<sub>2</sub> on Photosynthesis, Growth, and Elemental Ratios in Marine ''Synechococcus'' and ''Prochlorococcus'' (Cyanobacteria)|journal=Journal of Phycology|date=16 May 2007|volume=43|issue=3|pages=485–496|doi=10.1111/j.1529-8817.2007.00355.x|bibcode=2007JPcgy..43..485F |s2cid=53353243}}</ref> The abundance, distribution and all other characteristics of the ''Prochlorococcus'' make it a key organism in oligotrophic waters serving as an important primary producer to the open ocean food webs.

== Ecotypes ==
''Prochlorococcus'' has different [[Ecotype|"ecotypes"]] occupying different niches and can vary by pigments, light requirements, nitrogen and phosphorus utilization, copper, and virus sensitivity.<ref name=Scanlan99>{{cite journal |first1=N.J. |last1=West |first2=D.J. |last2=Scanlan |year=1999 |title=Niche-partitioning of ''Prochlorococcus'' in a stratified water column in the eastern North Atlantic Ocean |journal=[[Applied and Environmental Microbiology]] |volume=65 |issue=6 |pages=2585–91 |doi=10.1128/AEM.65.6.2585-2591.1999 |pmc=91382 |pmid=10347047 |doi-access=free}}</ref><ref name="Biller-2014" /><ref name=Rocap03/> It is thought that ''Prochlorococcus'' may occupy potentially 35 different ecotypes and sub-ecotypes within the worlds' oceans. They can be differentiated on the basis of the sequence of the [[ribosomal RNA]] gene.<ref name="Biller-2014" /><ref name=Scanlan99 /> It has been broken down by [[NCBI Taxonomy Browser|NCBI Taxonomy]] into two different subspecies, Low-light Adapted (LL) or High-light Adapted (HL).<ref name="NCBI" /> There are six clades within each subspecies.<ref name="Biller-2014" />

=== Low-light adapted ===
''Prochlorococcus marinus'' subsp. ''marinus'' is associated with low-light adapted types.<ref name="NCBI" /> It is also further classified by sub-ecotypes LLI-LLVII, where LLII/III has not been yet phylogenetically uncoupled.<ref name="Biller-2014" /><ref name="Yan-2020">{{Cite journal |last1=Yan |first1=Wei |last2=Feng |first2=Xuejin |last3=Zhang |first3=Wei |last4=Zhang |first4=Rui |last5=Jiao |first5=Nianzhi |date=2020-11-01 |title=Research advances on ecotype and sub-ecotype differentiation of ''Prochlorococcus'' and its environmental adaptability |url=https://doi.org/10.1007/s11430-020-9651-0 |journal=Science China Earth Sciences |language=en |volume=63 |issue=11 |pages=1691–1700 |doi=10.1007/s11430-020-9651-0 |bibcode=2020ScChD..63.1691Y |s2cid=221218462 |issn=1869-1897|url-access=subscription }}</ref> LV species are found in highly iron scarce locations around the equator, and as a result, have lost several ferric proteins.<ref name="Rusch-2010">{{Cite journal |last1=Rusch |first1=Douglas B. |last2=Martiny |first2=Adam C. |last3=Dupont |first3=Christopher L. |last4=Halpern |first4=Aaron L. |last5=Venter |first5=J. Craig |date=2010-09-14 |title=Characterization of ''Prochlorococcus'' clades from iron-depleted oceanic regions |journal=Proceedings of the National Academy of Sciences |language=en |volume=107 |issue=37 |pages=16184–9 |doi=10.1073/pnas.1009513107 |issn=0027-8424 |pmc=2941326 |pmid=20733077|bibcode=2010PNAS..10716184R |doi-access=free }}</ref> The low-light adapted subspecies is otherwise known to have a higher ratio of chlorophyll b2 to chlorophyll a2,<ref name=Scanlan99 /> which aids in its ability to absorb blue light.<ref>{{cite journal |last1=Ralf |first1=G. |last2=Repeta |first2=D. |year=1992 |title=The pigments of ''Prochlorococcus marinus'': The presence of divinylchlorophyll a and b in a marine prokaryote |journal=Limnology and Oceanography |volume=37 |issue=2 |pages=425–433 |bibcode=1992LimOc..37..425R |doi=10.4319/lo.1992.37.2.0425 |doi-access=free}}</ref> Blue light is able to penetrate ocean waters deeper than the rest of the visible spectrum, and can reach depths of >200&nbsp;m, depending on the turbidity of the water. Their ability to photosynthesize at a depth where blue light penetrates allows them to inhabit depths between 80 and 200 m.<ref name="Martiny" /><ref>{{cite journal |last1=Zinser |first1=E. |last2=Johnson |first2=Z. |last3=Coe |first3=A. |last4=Karaca |first4=E. |last5=Veneziano |first5=D. |last6=Chisholm |first6=S. |year=2007 |title=Influence of light and temperature on Prochlorococcus ecotype distributions in the Atlantic Ocean |journal=Limnology and Oceanography |volume=52 |issue=5 |pages=2205–20 |bibcode=2007LimOc..52.2205Z |doi=10.4319/lo.2007.52.5.2205|s2cid=84767930 |doi-access=free }}</ref> Their genomes can range from 1,650,000 to 2,600,000 basepairs in size.<ref name="Yan-2020" />

=== High-light adapted ===
''Prochlorococcus marinus'' subsp. ''pastoris'' is associated with high-light adapted types.<ref name="NCBI" /> It can be further classified by sub-ecotypes HLI-HLVI.<ref name="Yan-2020" /><ref name="Biller-2014" /> HLIII, like LV, is also located in an iron-limited environment near the equator, with similar ferric adaptations.<ref name="Rusch-2010" /> The high-light adapted subspecies is otherwise known to have a low ratio of chlorophyll b2 to chlorophyll a2.<ref name=Scanlan99 />  High-light adapted strains inhabit depths between 25 and 100&nbsp;m.<ref name="Martiny" /> Their genomes can range from 1,640,000 to 1,800,000 basepairs in size.<ref name="Yan-2020" />

== Metabolism ==
Most [[Cyanobacteria|cyanobacterium]] are known to have an incomplete [[tricarboxylic acid cycle]] (TCA).<ref>{{Cite journal |last1=García-Fernández |first1=Jose M. |last2=Diez |first2=Jesús |date=December 2004 |title=Adaptive mechanisms of nitrogen and carbon assimilatory pathways in the marine cyanobacteria ''Prochlorococcus'' |journal=Research in Microbiology |volume=155 |issue=10 |pages=795–802 |doi=10.1016/j.resmic.2004.06.009 |pmid=15567272 |issn=0923-2508|doi-access=free }}</ref><ref name="Zhang-2011">{{Cite journal |last1=Zhang |first1=Shuyi |last2=Bryant |first2=Donald A. |date=2011-12-16 |title=The Tricarboxylic Acid Cycle in Cyanobacteria |url=https://www.science.org/doi/10.1126/science.1210858 |journal=Science |language=en |volume=334 |issue=6062 |pages=1551–3 |doi=10.1126/science.1210858 |pmid=22174252 |bibcode=2011Sci...334.1551Z |s2cid=206536295 |issn=0036-8075|url-access=subscription }}</ref> In this process, [[2-oxoglutarate decarboxylase]] (2OGDC) and [[succinic semialdehyde dehydrogenase]] (SSADH), replace the enzyme [[2-oxoglutarate dehydrogenase]] (2-OGDH).<ref name="Zhang-2011" /> Normally, when this enzyme complex joins with [[NADP+]], it can be converted to succinate from [[2-Oxoglutarate|2-oxoglutarate]] (2-OG).<ref name="Zhang-2011" /> This pathway is non-functional in ''Prochlorococcus'',<ref name="Zhang-2011" /> as [[succinate dehydrogenase]] has been lost evolutionarily to conserve energy that may have otherwise been lost to phosphate metabolism.<ref>{{Cite journal |last1=Casey |first1=John R. |last2=Mardinoglu |first2=Adil |last3=Nielsen |first3=Jens |last4=Karl |first4=David M. |date=2016-12-27 |editor-last=Gutierrez |editor-first=Marcelino |title=Adaptive Evolution of Phosphorus Metabolism in ''Prochlorococcus'' |journal=mSystems |language=en |volume=1 |issue=6 |pages=e00065–16 |doi=10.1128/mSystems.00065-16 |issn=2379-5077 |pmc=5111396 |pmid=27868089}}</ref>

== Strains ==
{| class="wikitable"
|+
!Strain
!Subtype
!Source
|-
|MIT9515
|HLI
|<ref name="Kettler-2007" />
|-
|EQPAC1
|HLI
|<ref name="Biller-2014-2">{{Cite journal |last1=Biller |first1=Steven J. |last2=Berube |first2=Paul M. |last3=Berta-Thompson |first3=Jessie W. |last4=Kelly |first4=Libusha |last5=Roggensack |first5=Sara E. |last6=Awad |first6=Lana |last7=Roache-Johnson |first7=Kathryn H. |last8=Ding |first8=Huiming |last9=Giovannoni |first9=Stephen J. |last10=Rocap |first10=Gabrielle |last11=Moore |first11=Lisa R. |date=2014-09-30 |title=Genomes of diverse isolates of the marine cyanobacterium ''Prochlorococcus'' |journal=Scientific Data |language=en |volume=1 |issue=1 |pages=140034 |doi=10.1038/sdata.2014.34 |pmid=25977791 |pmc=4421930 |issn=2052-4463}}</ref>
|-
|MED4
|HLI
|<ref name=Rocap03 />
|-
|XMU1401
|HLII
|<ref>{{Cite journal |last1=Yan |first1=Wei |last2=Zhang |first2=Rui |last3=Wei |first3=Shuzhen |last4=Zeng |first4=Qinglu |last5=Xiao |first5=Xilin |last6=Wang |first6=Qiong |last7=Yan |first7=Hanrui |last8=Jiao |first8=Nianzhi |date=2018-01-11 |title=Draft Genome Sequence of ''Prochlorococcus marinus'' Strain XMU1401, Isolated from the Western Tropical North Pacific Ocean |journal=Genome Announcements |language=en |volume=6 |issue=2 |pages=e01431–17 |doi=10.1128/genomeA.01431-17 |issn=2169-8287 |pmc=5764940 |pmid=29326216}}</ref>
|-
|MIT0604
|HLII
|<ref name="Biller-2014-2" />
|-
|AS9601
|HLII
|<ref name="Kettler-2007" />
|-
|GP2
|HLII
|<ref name="Biller-2014-2" />
|-
|MIT9107
|HLII
|<ref name="Biller-2014-2" />
|-
|MIT9116
|HLII
|<ref name="Biller-2014-2" />
|-
|MIT9123
|HLII
|<ref name="Biller-2014-2" />
|-
|MIT9201
|HLII
|<ref name="Biller-2014-2" />
|-
|MIT9202 
|HLII
|<ref name="Biller-2014-2" />
|-
|MIT9215
|HLII
|<ref name="Kettler-2007" />
|-
|MIT9301
|HLII
|<ref name="Kettler-2007" />
|-
|MIT9302
|HLII
|<ref name="Biller-2014-2" />
|-
|MIT9311
|HLII
|<ref name="Biller-2014-2" />
|-
|MIT9312 
|HLII
|<ref name="Biller-2014-2" />
|-
|MIT9314 
|HLII
|<ref name="Biller-2014-2" />
|-
|MIT9321
|HLII
|<ref name="Biller-2014-2" />
|-
|MIT9322
|HLII
|<ref name="Biller-2014-2" />
|-
|MIT9401
|HLII
|<ref name="Biller-2014-2" />
|-
|SB
|HLII
|<ref name="Biller-2014-2" />
|-
|XMU1403
|LLI
|<ref name="Yan-2018">{{Cite journal |last1=Yan |first1=Wei |last2=Wei |first2=Shuzhen |last3=Wang |first3=Qiong |last4=Xiao |first4=Xilin |last5=Zeng |first5=Qinglu |last6=Jiao |first6=Nianzhi |last7=Zhang |first7=Rui |date=September 2018 |title=Genome Rearrangement Shapes ''Prochlorococcus'' Ecological Adaptation |journal=Applied and Environmental Microbiology |volume=84 |issue=17 |pages=e01178–18 |doi=10.1128/AEM.01178-18 |pmc=6102989 |pmid=29915114|bibcode=2018ApEnM..84E1178Y }}</ref>
|-
|XMU1408
|LLI
|<ref name="Yan-2018" />
|-
|MIT0801
|LLI
|<ref name="Biller-2014-2" />
|-
|NATL1A 
|LLI
|<ref name="Kettler-2007" />
|-
|NATL2A 
|LLI
|<ref name="Kettler-2007" />
|-
|PAC1
|LLI
|<ref name="Biller-2014-2" />
|-
|LG
|LLII/III
|<ref name="Biller-2014-2" />
|-
|MIT0601
|LLII/III
|<ref name="Biller-2014-2" />
|-
|MIT0602
|LLII/III
|<ref name="Biller-2014-2" />
|-
|MIT0603
|LLII/III
|<ref name="Biller-2014-2" />
|-
|MIT9211
|LLII/III
|<ref name="Kettler-2007" />
|-
|SS35
|LLII/III
|<ref name="Biller-2014-2" />
|-
|SS52
|LLII/III
|<ref name="Biller-2014-2" />
|-
|SS120
|LLII/III
|<ref name=Dufresne03>{{Cite journal |last1=Dufresne |first1=Alexis |last2=Salanoubat |first2=Marcel |last3=Partensky |first3=Frédéric |last4=Artiguenave |first4=François |last5=Axmann |first5=Ilka M. |last6=Barbe |first6=Valérie |last7=Duprat |first7=Simone |last8=Galperin |first8=Michael Y. |last9=Koonin |first9=Eugene V. |last10=Le Gall |first10=Florence |last11=Makarova |first11=Kira S. |date=2003-08-19 |title=Genome sequence of the cyanobacterium ''Prochlorococcus marinus'' SS120, a nearly minimal oxyphototrophic genome |journal=Proceedings of the National Academy of Sciences |volume=100 |issue=17 |pages=10020–5 |doi=10.1073/pnas.1733211100 |pmc=187748 |pmid=12917486|bibcode=2003PNAS..10010020D |doi-access=free }}</ref>
|-
|SS2
|LLII/III
|<ref name="Biller-2014-2" />
|-
|SS51
|LLII/III
|<ref name="Biller-2014-2" />
|-
|MIT0701
|LLIV
|<ref name="Biller-2014-2" />
|-
|MIT0702
|LLIV
|<ref name="Biller-2014-2" />
|-
|MIT0703
|LLIV
|<ref name="Biller-2014-2" />
|-
|MIT9303
|LLIV
|<ref name="Kettler-2007" />
|-
|MIT9313 
|LLIV
|<ref name="Kettler-2007" />
|-
|MIT1303
|LLIV
|<ref name="Cubillos-Ruiz-2017">{{Cite journal |last1=Cubillos-Ruiz |first1=Andres |last2=Berta-Thompson |first2=Jessie W. |last3=Becker |first3=Jamie W. |last4=van der Donk |first4=Wilfred A. |last5=Chisholm |first5=Sallie W. |date=2017-07-03 |title=Evolutionary radiation of lanthipeptides in marine cyanobacteria |journal=Proceedings of the National Academy of Sciences |volume=114 |issue=27 |pages=E5424–33 |doi=10.1073/pnas.1700990114 |pmc=5502607 |pmid=28630351|bibcode=2017PNAS..114E5424C |doi-access=free }}</ref>
|-
|MIT1306
|LLIV
|<ref name="Cubillos-Ruiz-2017" />
|-
|MIT1312
|LLIV
|<ref name="Cubillos-Ruiz-2017" />
|-
|MIT1313
|LLIV
|<ref name="Cubillos-Ruiz-2017" />
|-
|MIT1318
|LLIV
|<ref name="Cubillos-Ruiz-2017" />
|-
|MIT1320 
|LLIV
|<ref name="Cubillos-Ruiz-2017" />
|-
|MIT1323
|LLIV
|<ref name="Cubillos-Ruiz-2017" />
|-
|MIT1327
|LLIV
|<ref name="Cubillos-Ruiz-2017" />
|-
|MIT1342
|LLIV
|<ref name="Cubillos-Ruiz-2017" />
|}
Table modified from <ref name="Yan-2020" />

==See also==
* [[Photosynthetic picoplankton]]
* ''[[Pelagibacter]]''
* ''[[Synechococcus]]''

==References==
{{Reflist|30em}}

==Further reading==
{{refbegin}}
*{{cite journal |doi=10.4319/lo.1994.39.4.0954 |first1=L. |last1=Campbell |first2=H.A. |last2=Nolla |first3=D. |last3=Vaulot |year=1994 |title=The importance of ''Prochlorococcus'' to community structure in the central North Pacific Ocean |journal=[[Limnology and Oceanography]] |volume=39 |pages=954–961 |issue=4|bibcode=1994LimOc..39..954C |doi-access=free }}
*{{cite journal |first1=Jagroop |last1=Pandhal |first2=Phillip C. |last2=Wright |first3=Catherine A. |last3=Biggs |year=2007 |title=A quantitative proteomic analysis of light adaptation in a globally significant marine cyanobacterium ''Prochlorococcus marinus'' MED4 |journal=[[Journal of Proteome Research]] |volume=6 |issue=3 |pages=996–1005 |doi=10.1021/pr060460c|pmid=17298086 }}
*{{cite journal |first=Steve |last=Nadis |title=The cells that rule the seas: the ocean's tiniest inhabitants, notes biological researcher Sallie W. Chisholm, hold the key to understanding the biosphere — and what happens when humans disrupt it |journal=[[Scientific American]] |year=2003 |volume=289 |issue=6 |pages=52–53 |pmid=14631732 |doi=10.1038/scientificamerican1203-52 |url=https://www.scientificamerican.com/article/the-cells-that-rule-the-s/|url-access=subscription }}
*{{cite journal |first=Melissa |last=Garren |title=The sea we've hardly seen |journal=[[TEDx Monterey]] |year=2012 |pages=52f |url=http://www.ted.com/talks/melissa_garren_the_sea_we_ve_hardly_seen.html |access-date=2012-06-22 |archive-date=2013-12-02 |archive-url=https://web.archive.org/web/20131202224203/http://www.ted.com/talks/melissa_garren_the_sea_we_ve_hardly_seen.html |url-status=dead }}
{{refend}}

==External links==
*[https://www.npr.org/templates/story/story.php?storyId=91448837 The Most Important Microbe You've Never Heard Of]: [[NPR]] Story on ''Prochlorococcus''

{{Taxonbar|from=Q18645284|from2=Q310210}}

[[Category:Synechococcales]]
[[Category:Environmental microbiology]]
[[Category:Monotypic bacteria genera]]
[[Category:Cyanobacteria genera]]
[[Category:Marine microorganisms]]