Picozoa

{{Short description|Phylum of marine unicellular heterotrophic eukaryotes}} {{Speciesbox | image = Picomonas-judraskeda-Gen.-Et-Sp.-Nov.-The-First-Identified-Member-of-the-Picozoa-Phylum-Nov.-a-pone.0059565.s004.ogv | image_caption = Movement of a ''Picomonas judraskeda'' cell | image2 = Picomonas-judraskeda-Gen.-Et-Sp.-Nov.-The-First-Identified-Member-of-the-Picozoa-Phylum-Nov.-a-pone.0059565.s005.ogv | image2_caption = Animation of the 3D structure of ''Picomonas judraskeda'' | greatgreatgreatgrandparent_authority = Seenivasan ''et al.'' 2013 | greatgreatgrandparent_authority = Seenivasan ''et al.'' 2013 | greatgrandparent_authority = Seenivasan ''et al.'' 2013 | grandparent_authority = Seenivasan ''et al.'' 2013 | parent_authority = Seenivasan ''et al.'' 2013 | display_parents = 6 | genus = Picomonas | species = judraskeda | authority = Seenivasan ''et al.'' 2013 | synonyms = *Picobiliphyta }}

'''Picozoa''', '''Picobiliphyta''', '''picobiliphytes''', or '''piliphytes''' are protists of a phylum of marine unicellular heterotrophic eukaryotes with a size of less than about 3 micrometers. They were formerly treated as eukaryotic algae and the smallest member of photosynthetic picoplankton before it was discovered they do not perform photosynthesis.<ref name="Moreira2014">{{cite journal | vauthors = Moreira D, López-García P | title = The rise and fall of Picobiliphytes: how assumed autotrophs turned out to be heterotrophs | journal = BioEssays | volume = 36 | issue = 5 | pages = 468–474 | date = May 2014 | pmid = 24615955 | pmc = 4133654 | doi = 10.1002/bies.201300176 }}</ref> The phylum currently contains a single species, '''''Picomonas judraskeda'''''.<ref name="Seenivasan2013">{{cite journal | vauthors = Seenivasan R, Sausen N, Medlin LK, Melkonian M | title = Picomonas judraskeda gen. et sp. nov.: the first identified member of the Picozoa phylum nov., a widespread group of picoeukaryotes, formerly known as 'picobiliphytes' | journal = PLOS ONE | volume = 8 | issue = 3 | article-number = e59565 | year = 2013 | pmid = 23555709 | pmc = 3608682 | doi = 10.1371/journal.pone.0059565 | veditors = Waller RF | doi-access = free | bibcode = 2013PLoSO...859565S }}</ref> They probably belong in the Archaeplastida as sister of the Rhodophyta.<ref>{{cite journal | vauthors = Burki F, Kaplan M, Tikhonenkov DV, Zlatogursky V, Minh BQ, Radaykina LV, Smirnov A, Mylnikov AP, Keeling PJ | display-authors = 6 | title = Untangling the early diversification of eukaryotes: a phylogenomic study of the evolutionary origins of Centrohelida, Haptophyta and Cryptista | journal = Proceedings. Biological Sciences | volume = 283 | issue = 1823 | article-number = 20152802 | date = January 2016 | pmid = 26817772 | pmc = 4795036 | doi = 10.1098/rspb.2015.2802 }}</ref><ref>{{cite journal | vauthors = Lax G, Eglit Y, Eme L, Bertrand EM, Roger AJ, Simpson AG | title = Hemimastigophora is a novel supra-kingdom-level lineage of eukaryotes | language = En | journal = Nature | volume = 564 | issue = 7736 | pages = 410–414 | date = December 2018 | pmid = 30429611 | doi = 10.1038/s41586-018-0708-8 | s2cid = 205570993 | bibcode = 2018Natur.564..410L }}</ref><ref>{{cite bioRxiv |last1=Yazaki |first1=Euki |last2=Yabuki |first2=Akinori |last3=Imaizumi |first3=Ayaka |last4=Kume |first4=Keitaro |last5=Hashimoto |first5=Tetsuo |last6=Inagaki |first6=Yuji |title=Phylogenomics invokes the clade housing Cryptista, Archaeplastida, and ''Microheliella maris'' |biorxiv=10.1101/2021.08.29.458128 |date=31 August 2021}}</ref><ref>{{cite journal |last1=Schön |first1=M.E. |last2=Zlatogursky |first2=V.V. |last3=Singh |first3=R.P. |display-authors=et al. |title=Single cell genomics reveals plastid-lacking Picozoa are close relatives of red algae |journal=Nature Communications |date=17 November 2021 |volume=12: 6651 |issue=1 |page=6651 |doi=10.1038/s41467-021-26918-0 |pmid=34789758 |issn=2041-1723 |pmc=8599508|bibcode=2021NatCo..12.6651S }}</ref><ref>{{Cite journal |last=Cavalier-Smith |first=Thomas |date=2022-05-01 |title=Ciliary transition zone evolution and the root of the eukaryote tree: implications for opisthokont origin and classification of kingdoms Protozoa, Plantae, and Fungi |journal=Protoplasma |language=en |volume=259 |issue=3 |pages=487–593 |doi=10.1007/s00709-021-01665-7 |issn=1615-6102 |pmc=9010356 |pmid=34940909}}</ref>

They were formerly placed within the cryptomonads-haptophytes assemblage.<ref name="urlEukaryotes">{{cite web | vauthors = Keeling P, Leander BS | date = 28 October 2009 |orig-date = 8 September 2000 |url=http://tolweb.org/Eukaryotes/3|title=Eukaryotes|access-date=2009-06-17 | work = Tree of Life Web Project }}</ref>

== Discovery == At the end of the 1990s, the European project "Picodiv" clarified which organisms occur in picoplankton. In addition, for a period of two years, samples were taken in the Atlantic, in the Mediterranean, before the coast of Scotland, Alaska and Norway.<ref>{{cite journal | vauthors = Massana R, Guillou L, Díez B, Pedrós-Alió C | title = Unveiling the organisms behind novel eukaryotic ribosomal DNA sequences from the ocean | journal = Applied and Environmental Microbiology | volume = 68 | issue = 9 | pages = 4554–4558 | date = September 2002 | pmid = 12200313 | pmc = 124113 | doi = 10.1128/AEM.68.9.4554-4558.2002 | bibcode = 2002ApEnM..68.4554M }}</ref>{{Citation needed|date=November 2021}} Picozoa were found particularly within the nutrient-poor ranges from cold coastal seas, where they can constitute up to 50 percent of the biomass.{{Citation needed|date=November 2021}}

== Affinities to other organisms ==

thumb|upright=0.5|''Picomonas judraskeda''

Picozoa were first detected using 18S ribosomal RNA genes in 2007.<ref name=":1">{{cite journal | vauthors = Not F, Valentin K, Romari K, Lovejoy C, Massana R, Töbe K, Vaulot D, Medlin LK | display-authors = 6 | title = Picobiliphytes: A Marine Picoplanktonic Algal Group with Unknown Affinities to Other Eukaryotes | journal = Science | volume = 315 | issue = 5809 | pages = 253–255 | date = January 2007 | pmid = 17218530 | doi = 10.1126/science.1136264 | bibcode = 2007Sci...315..253N | s2cid = 22285394 | url = https://epic.awi.de/id/eprint/16025/1/Not2006a.pdf | author-link8 = Linda Medlin }}</ref> The identity of new organisms was deduced from a comparison of familiar and unfamiliar gene sequences. "The gene sequences found in these algae could not be associated with any previously known group of organisms", explain Klaus Valentin and Linda Medlin, co-authors of the study and molecular biologists at the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven.<ref name=":0">{{Cite web|date=January 15, 2007|title=New Group Of Algae Discovered: Picobiliphytes|url=https://www.sciencedaily.com/releases/2007/01/070111181710.htm|access-date=2021-11-01|website=ScienceDaily|language=en}}</ref> The algae in this study were found in plankton samples originating from various regions of the North Atlantic and the Mediterranean. The scientists have discovered a group of organisms which, despite being completely new to science, have a wide distribution. "This is a good indication for how much there is still to discover in the oceans, especially using molecular tools", says Valentin.<ref name=":0" />

Apart from the unfamiliar gene sequences, the researchers also detected phycobiliproteins.<ref name="urlBizarre New Form of Life Found in Arctic Ocean, Scientists Announce">{{cite web | vauthors = Hearn K | work = National Geographic News | date = 11 January 2007 |url=http://news.nationalgeographic.com/news/2007/01/070111-new-lifeform.html | archive-url = https://web.archive.org/web/20080211105739/https://news.nationalgeographic.com/news/2007/01/070111-new-lifeform.html | archive-date = 11 February 2008 |title=Bizarre New Form of Life Found in Arctic Ocean, Scientists Announce|access-date=2009-06-17}}</ref> In red algae, for example, these proteins occur as pigments. But in this newly discovered group of algae, the phycobiliproteins appear to be contained inside the plastids,<ref name="isbn3-540-68692-4">{{cite book|title=The Chloroplast: Interactions with the Environment (Plant Cell Monographs)| vauthors = Aronsson H, Sandelius AS |publisher=Springer|year=2008|isbn=978-3-540-68692-7|location=Berlin|page=9}}</ref> where the photosynthesis occurs. Hence, it provides a clear indication that the researchers are dealing with previously unidentified group of algae. Referring to their small size and the presence of phycobiliproteins, the researchers named the new group picobiliphytes.<ref name=":1" />

Two studies published in 2011 found the hypothesis that biliphytes, or picobiliphytes, were photosynthetic was likely to be false. A 2011 study by an international team from the Monterey Bay Aquarium Research Institute, Dalhousie University and the Natural History Museum London found that cells in the Pacific Ocean did not have fluorescence indicative of photosynthetic pigments, and concluded "...biliphytes are likely not obligate photoautotrophs but rather facultative mixotrophs or phagotrophs, whereby transient detection of orange fluorescence could represent ingested prey items (e.g., the cyanobacterium ''Synechococcus'')".<ref>{{cite journal | vauthors = Kim E, Harrison JW, Sudek S, Jones MD, Wilcox HM, Richards TA, Worden AZ, Archibald JM | display-authors = 6 | title = Newly identified and diverse plastid-bearing branch on the eukaryotic tree of life | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 108 | issue = 4 | pages = 1496–1500 | date = January 2011 | pmid = 21205890 | pmc = 3029697 | doi = 10.1073/pnas.1013337108 | doi-access = free | bibcode = 2011PNAS..108.1496K }}</ref> A study later in 2011, conducted by researchers at Rutgers University and Bigelow Laboratory for Ocean Sciences, used whole genome shotgun sequence data from three individual picobiliphyte cells to show absence of plastid-targeted or photosystem proteins within the fragments of nuclear genome sequence they reconstructed. This again suggested that picobiliphytes are heterotrophs.<ref name="PicoSAG">{{cite journal | vauthors = Yoon HS, Price DC, Stepanauskas R, Rajah VD, Sieracki ME, Wilson WH, Yang EC, Duffy S, Bhattacharya D | display-authors = 6 | title = Single-cell genomics reveals organismal interactions in uncultivated marine protists | journal = Science | volume = 332 | issue = 6030 | pages = 714–717 | date = May 2011 | pmid = 21551060 | doi = 10.1126/science.1203163 | s2cid = 34343205 | bibcode = 2011Sci...332..714Y }}</ref><ref>{{cite journal | vauthors = Worden AZ, Dupont C, Allen AE | title = Genomes of uncultured eukaryotes: sorting FACS from fiction | journal = Genome Biology | volume = 12 | issue = 6 | page = 117 | date = June 2011 | pmid = 21722350 | pmc = 3218834 | doi = 10.1186/gb-2011-12-6-117 | doi-access = free }}</ref>

In 2013, Seenivasan working in conjunction with Michael Melkonian (University of Cologne) and Linda Medlin (Marine Biological Association of the UK) formally described the picobiliphytes as the heterotrophic nanoflagellate phylum, Picozoa, and published thin sections of the cells.<ref name="Seenivasan2013"/> Several unique features in the cell, such as a feeding organelle, unusual movement, and heterotrophic mode of nutrition, substantiate their unique phylogenetic position. No traces of viral or bacterial particles were found inside these heterotrophic cells, which prompted these authors to suggest that they feed on small organic particles.<ref name="Seenivasan2013"/>

== See also == * Microphyte * Picoeukaryote * Picocyanobacteria * Picoplankton * Biliphyta

== References == {{Reflist}}

== External links == * {{Commons category-inline|Picozoa}} * {{Wikispecies-inline}} * [http://idw-online.de/pages/de/news191572 Neue Algengruppe entdeckt: Picobiliphyta] {{in lang|de}} * [https://www.sciencedaily.com/releases/2007/01/070111181710.htm New Group Of Algae Discovered: Picobiliphytes] {{in lang|en}} * [http://tolweb.org/Biliphytes/121508 Tree of Life: Biliphytes]

{{Life on Earth}} {{Eukaryota|D.}} {{Taxonbar|from=Q10640455}}

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