Cryptophyceae

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Cryptophyceae
Rhodomonas salina

Rhodomonas salina

Systematics
Classification : Creature
Domain : Eukaryotes (Eucaryota)
without rank: Chromalveolata
without rank: Cryptophyta
Class : Cryptophyceae
Scientific name
Cryptophyceae
Pascher 1913, emend. Schoenichen , 1925

The Cryptophyceae (from ancient Greek Κρύπτος secret and Φύκιον algae ) are a class of unicellular, microscopic algae that occur in fresh and seawater. The Cryptophyceae move through the water with the help of two flagella and can be reddish, bluish or brownish in color. Some Cryptophyceae form thick-walled and spherical permanent stages in order to survive unfavorable environmental conditions. As an ecologically very important group of algae, the Cryptophyceae serve many protists as food. Since the Cryptophyceae belong to colorless and photosynthetically active genera or species, there are botanical and zoological classifications. They can therefore be referred to zoologically as cryptomonads . However, their evolutionary history and its resulting affinities ago they are systematically neither the animals nor the plants (on the instantaneous state of knowledge are in the kingdom Plantae sensu Archaeplastida the Glaucophyten , red algae and Viridiplantae with green algae and land plants combined). The closest relatives of cryptophyceae are the most colorless and phagotroph living Katablepharidophyta . Together they form the taxon of the Cryptophyta .

Most of the Cryptophyceae (from ancient Greek Κρύπτο, "Crypto" Secret and φύκιον "Phykion" Alga) with the exception of the genus Goniomonas have two cell nuclei of different evolutionary origins and have therefore become of interest to evolutionary biologists. The different cell compartments are nested like a matryoshka . The outermost compartment contains the actual cell nucleus and the cytoplasm , in which the mitochondria are also located. The next smaller so-called periplastid compartment contains the second strongly reduced nucleus ( nucleomorph ) and starch granules. The innermost compartment is the actual photosynthesis organelle , the plastid . Since mitochondria and plastids also have their own genomes (mitogenome, plastome), a Cryptophycean cell contains a total of four genomes.

Schematic cell structure:
1 : contractile vacuole
2 : plastid or chloroplast
3 : thylakoid
4 : eye spot (stigma)
5 : nucleomorph
6 : starch body (granules),
7 : 70S ribosome
8 : cell nucleus (nucleus)
9 : 80S ribosome
10 : Flagella
11 : Cell invagination (intussusception)
12 : Lipid globules
13 : Ejectosomes
14 : Mitochondrion ,
15 : Pyrenoid
16 : Golgi apparatus
17 :  Endoplasmic reticulum (ER)
18 : ER of the complex plastid / chloroplast .

The large number of genomes is explained by a secondary endosymbiosis, in which a phagotrophic eukaryote ingested a photosynthetically active eukaryote. Ingested organisms are normally digested. In the case of an endosymbiosis , however, the absorbed cell is retained and, over time, transforms into a dependent organelle . However, only in the case of the Chlorarachniophyta and the Cryptophyceae, which are not related to them, the nucleus of the ingested algae was not lost.

The marine Cryptophycee Guillardia theta was chosen as a model organism to sequence the genomes of nucleomorphs and plastids . Both genome sequencing showed that the plastid of the Cryptophyceae must originally have been a red alga. Further evidence for this theory are the starch synthesis and the 80S ribosomes in the periplastid space (the former cytoplasm of the ingested red alga) and the four envelope membranes that surround the plastids. All plastids that originate from a primary endosymbiosis (the chloroplasts of green algae and land plants, the cyanelles of glaucocystophytes and the rhodoplasts of red algae) are separated by only two covering membranes and not by three or four (= complex plastids ).

Systematics of the Cryptophyceae

The systematic division of the Cryptophyceae into different genera has so far been mainly based on morphological features and pigmentation .

  1. One of the most important features here is the periplast . The periplast is a layered cell envelope - Cryptophyceae do not form a cell wall - consisting of an inner and an outer periplast component made of proteins. In between lies the cell's plasma membrane . Both peripheral components show very fine structures. The inner periplastic component can e.g. B. consist of polygonal plates, overlapping rectangular plates or a continuous layer. The outer periplastic component can also be composed of plates or rosette scales and fine fibrils.
  2. All cryptophyceae have a Zelleinstülpung (intussusception), the explosive organelles, the so-called. Ejekto - or Ejektisomen is lined (see extrusome ). The opening of this cell protuberance can either be small with a blindly ending sack behind it (gullet) or elongated following the cell protuberance (furrow). Combinations of furrow and throat are also possible.
  3. In some genera, the nucleomorph is not free in the periplastid space, but is embedded in the pyrenoid matrix (spatially separated by the two inner enveloping membranes of the plastid).
  4. Of the phycobilisomes , the light-harvesting complexes of red algae (and glaucocystophyceae and cyanobacteria ), which originally contained three different blue or red pigments, only phycoerythrin remained in the cryptophyceae. In the Cryptophyceae, however, seven different phycoerythrin types evolved from the originally red phycoerythrin, four of which are colored blue and are therefore called phycocyanins, although they are not directly related to the real phycocyanins from the phycobilisomes.
  5. The microtubular flagella roots , with which the flagella are anchored in the cells, also show differences.

From the combination of the different characteristics

  • Structure of the periplast,
  • Shape of the cell protuberance,
  • Position of the nucleomorph,
  • Pigment type and
  • Structure of the flagellum apparatus

the different genera result.

The investigation of the relationships within the Cryptophyceae using methods of molecular-phylogenetic analysis (= creation of family trees based on DNA sequences), however, revealed a much more complex picture. Cryptophyceae are likely to be dimorphic; that is, they can form two different cell types. Therefore, two cell forms of one genus were probably mistakenly mistaken for two different genera. Dimorphism was definitely proven in the genera Proteomonas and Cryptomonas . Even a leukoplast , a colorless plastid that has lost the ability to photosynthesize, is not a reliable feature of an independent genus. The former genus Chilomonas turned out to be a colorless Cryptomonas , of which at least three different evolutionary lines exist within Cryptomonas . The other genera of the Cryptophyceae probably also require a revision of their systematics.

Genres of cryptophyceae according to preliminary state of research: chroomonas , Crypto Monas (includes the formerly independent genera Campylomonas and Chilomonas ) Geminigera , Goniomonas , Guillardia , Hanusia , Hemiselmis , comma , Plagioselmis , Proteo Monas , Rhino Monas , Rhodomonas ( Pyrenomonas ) Teleaulax .

literature

  1. ^ Karl-Heinz Linne von Berg, Michael Melkonian a. a .: The Kosmos algae guide. The most important freshwater algae under the microscope. Kosmos, Stuttgart 2004, ISBN 3-440-09719-6 .
  2. ↑ Saunders GW, Hommersand M. (2004). Assessing red algal supraordinal diversity and taxonomy in the context of contemporary systematic data. American Journal of Botany 91: pp. 1494-1507
  3. ↑ Okamoto N., Inouye I. (2005): The Katablepharids are a distant sister group of the Cryptophyta: A proposal for Katablepharidophyta divisio nova / Kathablepharida phylum novum based on SSU rDNA and beta-tubulin phylogeny. Protist 156: pp. 163-179
  4. ^ Douglas SE, Penny SL (1999): The plastid genome of the cryptophyte alga, Guillardia theta: complete sequence and conserved synteny groups confirm its common ancestry with red algae. Journal of Molecular Evolution 48: pp. 236-244
  5. ^ Douglas SE, Zauner S., Fraunholz M., Beaton M., Penny S., Deng LT, Wu X., Reith M., T. Cavalier-Smith , U.-F. Maier (2001): The highly reduced genome of an enslaved algal nucleus. Nature (London) 410: pp. 1040-1041
  6. ^ A b D. RA Hill, R. Wetherbee (1986): Proteomonas sulcata gen. Et sp. nov. (Cryptophyceae), a cryptomonad with two morphologically distinct and alternating forms. Phycologia 25: pp. 521-543
  7. ↑ a b c Hoef-Emden K, Melkonian M (2003): Revision of the genus Cryptomonas (Cryptophyceae): a combination of molecular phylogeny and morphology provides insights in a long-hidden dimorphism. Protist 154: pp. 371-409
  8. ↑ K. Hoef-Emden (2005): Multiple independent losses of photosynthesis and differing evolutionary rates in the genus Cryptomonas (Cryptophyceae): combined phylogenetic analyzes of DNA sequences of the nuclear and nucleomorphic ribosomal operons. Journal of Molecular Evolution 60: pp. 183-195
  9. ↑ Deane JA, Strachan IM, Saunders GW, Hill DRA, McFadden GI (2002): Cryptomonad evolution: nuclear 18S rDNA phylogeny versus cell morphology and pigmentation. Journal of Phycology 38: pp. 1236-1244
  10. ^ Hoef-Emden K, Marin B, Melkonian M (2002): Nuclear and nucleomorphic SSU rDNA phylogeny in the Cryptophyta and the evolution of cryptophyte diversity. Journal of Molecular Evolution 55: pp. 161-179
  11. ↑ Marin B., Klingberg M., Melkonian M. (1998): Phylogenetic relationships among the Cryptophyta: analyzes of nuclear-encoded SSU rRNA sequences support the monophyly of extant plastid containing lineages. Protist 149: pp. 265-276
  12. ↑ Deane JA, Hill DRA, Brett SJ, McFadden GI (1998): Hanusia phi gen. Et sp. nov. (Cryptophyceae): Characterization of 'Cryptomonas' sp. theta '. European Journal of Phycology 33: pp. 149-154
  13. ↑ Hill DRA (1991a): A revised circumscription of Cryptomonas (Cryptophyceae) based on an examination of Australian strains. Phycologia 30: pp. 170-188
  14. ↑ Hill DRA (1991b): A Chroomonas and other blue-green cryptomonads. Journal of Phycology 27: pp. 133-145
  15. ↑ Hill DRA, Wetherbee R. (1988): The structure and taxonomy of Rhinomonas pauca gen. Et sp. nov. (Cryptophyceae). Phycologia 27: pp. 355-365
  16. ↑ Hill DRA, Wetherbee R. (1989): A reappraisal of the genus Rhodomonas (Cryptophyceae). Phycologia 28: pp. 143-158
  17. Jump up ↑ Hill DRA, Wetherbee R. (1990). Guillardia theta gen. Et sp. nov. (Cryptophyceae). Canadian Journal of Botany 68: pp. 1873-1876
  18. ↑ McFadden GI, Gilson PR, Hill DRA (1994): Goniomonas: rRNA sequences indicate that this phagotrophic flagellate is a close relative of the host component of cryptomonads. European Journal of Phycology 29: pp. 29-32

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