Prasinococcus
| Prasinococcus | |
|---|---|
Scientific classification
| |
| (unranked): | Viridiplantae |
| Phylum: | Prasinodermophyta |
| Class: | Palmophyllophyceae |
| Order: | Prasinococcales |
| Family: | Prasinococcaceae |
| Genus: | Prasinococcus Miyashita & Chihara 1993[1] |
| Species: | P. capsulatus
|
| Binomial name | |
| Prasinococcus capsulatus Miyashita & Chihara 1993[1]
| |
Prasinococcusis amonotypicgenusofgreen algae,containing the only speciesPrasinococcus capsulatus,in the monotypic familyPrasinococcaceae.[2]Thisunicellularalgal species was discovered in 1990 in the WestPacific Oceanand has characteristic reproduction methods as well as an interesting and potentially exploitable morphology. This is the only species in the genus, though variousstrainsexist, for example URI 266G is theAtlanticclone.[3]
Discovery
[edit]Prasinococcus capsulatus,the only currently known member of this genus, was discovered in the WestPacific Oceanduring a cruise by the research vessel Sohgen-maru in November–December 1990. The name "'capsulatus'" coming from the alga's large capsule which surrounds the cell.[1]
Morphology
[edit]Prasinococcushave a firmcell walllackingscalesand also lackflagella.The mitochondrial lobe andchloroplastouter membrane both protrude into thepyrenoidmatrix which is considered characteristic of the genus. The cell wall has a protruding circular collar which is surrounded by holes which penetrate the cell wall. Its method ofasexual reproductionis also considered characteristic - after cell division one daughter cell remains within the original cell wall while the other is extruded.[1]
The most notable feature ofP. capsulatusmorphology is its large capsule composed of an exo-polysaccharidewhich has been dubbed "capsulan".Capsulan is thought to be synthesised in theGolgiand then secreted through the decapore (a specialised circle of 10 pores through thecell wall). After exiting the decapore capsulan becomes visible and it is thought that it cross links withdivalentionsin the seawater. Research is currently underway to find potential applications for capsulan and how to maximise its production.[3]
The capsule's function is not clearly defined but various explanations have been suggested. One is that it offers protection to newly divided cells which lack a thick cell wall, another is that it provides a template for daughter cells to synthesise their new cell wall. The capsule may also interfere with filter feeding, thus reducing predation. In similar species, capsules have been noted for theirantibacterialproperties[4]and a conspicuous lack ofbacteriaas well asviral particlesin impure samples ofP. capsulatushas been observed.[3]
ThepigmentsofPrasinococcusinclude chlorophylls a and b, prasinoxanthin, Mg 2, 4-diviriylphaeoporphyrin a5 monomethyl ester (Mg 2, 4-D) and 5, 6-epoxy-3, 3′-dihydroxy-5, 6, 7′, 8′-tetrahydro-β-ε-caroten-11′ and 19-olide (uriolide).[1]
Reproduction
[edit]Sexual reproductionhas not been observed inP. capsulatusbut its mode of asexual reproduction is quite distinctive. The cell splits into twodaughtercells while remaining inside the original cell wall, one daughter cell then begins to enlarge, while the other is pushed out of a small hole in the parental cell wall. The larger cell remains in the original cell wall while the other migrates to the edge of the capsule which surrounds them both. Before leaving the parental capsule this daughter has synthesised its own firm cell wall after which it leaves the parental capsule and begins to produce its own capsule.[1]
Others claim that this mode of reproduction immature cells with thinner walls older cells with thicker walls must first discard the paternal cell wall before undergoingbinary fissionand then each daughter cell produces its own new cell wall. This is evidenced by abandoned cell walls residing in mature cells' capsules.[3]
Distribution
[edit]P. capsulatusis an important contributor to oceanicbiomassespecially in late winter to early spring. Its range covers much of the West Pacific and WestAtlanticOceans.[3]
Bio-remediation
[edit]P. capsulatusis currently being studied for use inCarbon Dioxidecapture, especially important as it recycles this carbon into capsulan which may be a useful compound.[5]
References
[edit]- ^abcdefMiyashita, Hideaki; Ikemoto, Hisato; Kurano, Norihide; Miyachi, Sigetoh; Chihara, Mitsuo (1993)."Prasinococcus capsulatus gen. Et sp. Nov., a new marine coccoid prasinophyte".The Journal of General and Applied Microbiology.39(6): 571–582.doi:10.2323/jgam.39.571.
- ^Guiry, M.D.; Guiry, G.M."Prasinococcaceae".AlgaeBase.World-wide electronic publication, National University of Ireland, Galway.
- ^abcdeSieburth, John McN.; Keller, Maureen D.; Johnson, Paul W.; Myklestad, Sverre M. (October 1999). "WIDESPREAD OCCURRENCE OF THE OCEANIC ULTRAPLANKTER,PRASINOCOCCUS CAPSULATUS(PRASINOPHYCEAE), THE DIAGNOSTIC "GOLGI-DECAPORE COMPLEX" AND THE NEWLY DESCRIBED POLYSACCHARIDE "CAPSULAN"".Journal of Phycology.35(5): 1032–1043.doi:10.1046/j.1529-8817.1999.3551032.x.S2CID86059264.
- ^Davidson AT, Marchant HJ (1987). "Binding of manganese by AntarcticPhaeocystis pouchetiiand the role of bacteria in its release ".Marine Biology.95(3): 481–487.doi:10.1007/BF00409577.S2CID84709702.
- ^Kurano N, Ikemoto H, Miyashita H, Hasegawa T, Hata H, Miyachi S (1995). "Fixation and utilization of carbon dioxide by microalgal photosynthesis".Energy Conversion and Management.36(6–9): 689–692.doi:10.1016/0196-8904(95)00099-Y.