Cyclotella
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Cyclotella | |
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Cyclotella meneghiniana | |
Scientific classification | |
Domain: | Eukaryota |
Clade: | Diaphoretickes |
Clade: | SAR |
Clade: | Stramenopiles |
Phylum: | Gyrista |
Subphylum: | Ochrophytina |
Class: | Bacillariophyceae |
Order: | Thalassiosirales |
Family: | Stephanodiscaceae |
Genus: | Cyclotella (Kützing) de Brebisson |
Cyclotella is a genus of diatoms often found in oligotrophic environments, both marine and fresh water. It is in the family Stephanodiscaceae and the order Thalassiosirales.[1] The genus was first discovered in the mid-1800s and since then has become an umbrella genus for nearly 100 different species, the most well-studied and the best known being Cyclotella meneghiniana. Despite being among the most dominant genera in low-productivity environments, it is relatively understudied.[2]
Cyclotella's habitat has traditionally been described as low-productivity
Etymology
The name Cyclotella is derived from the Greek term kyklos, meaning "circle." While "circle" can be used to describe many diatoms, Cyclotella spp. are all circular and have a girdle band arrangement that makes the structure of the organism resemble a wheel.[4]
History
The genus Cyclotella was described in 1838 by
As Brébisson describes in the 1838 publication Flore de Normandie, Cyclotella "has a more or less elongated ovoid shape, it is swollen from both sides, and when its center is diaphanous, it resembles two tubular frustules united by their vertices ( translated from French )." Many databases, texts, and members of the scientific community refer to the entire genus of Cyclotella as Cyclotella (Kützing) Brébisson.[6] This full genus title indicates that Kützing initially discovered species of a genera and put them into another genus, which was then altered by Brébisson who took some of those same species and placed them within the Cyclotella genus.[original research?] Upon distinguishing Cyclotella from other diatom species, there have been nearly 100 different species of the genus described and taxonomically accepted.[citation needed]
Habitat and ecology
Species of Cyclotella are most often found in
In a study performed in 1974, it was determined that the optimal
Another study by Van de Vijver and Dessein found a new species of Cyclotella, C. deceusteriana, in the sub-antarctic region.[9] One of the only ecological characteristics of Cyclotella that is consistent among most of its species is the fact that they are found in stagnant or near-stagnant waters and are immobile. Beyond that, there is a great deal of variation. Many of the Cyclotella species that have been studied have been shown to be found in aquatic environments that are either slightly or highly alkaline. C. distinguenda is known to prefer alkaline waters, and C. gamma has been found in lakes that have a pH range of 7.2 to 7.8. Nutrient concentration in the habitats of Cyclotella spp. varies. C. sensulato has been described as a dominant member of both mesotrophic and oligotrophic environments,[2] as many are, but both C. atomus and C. meneghiniana are found to prefer nutrient-rich environments. Temperature ranges vary between species as well; it was mentioned earlier that C. deceusteriana was discovered in sub-antarctic regions, and C. gamma and C.quillensis have been found in the Northern United States and Saskatchewan, respectively. C. atomus, on the other hand, has been found in warmer lake sediments in California. Colonization patterns of Cyclotella spp. are relatively uniform, in the sense that most of them are solitary organisms. C. meneghiniana, however, has been described to occasionally live in colonies.[10] Of course, the preference of nutrient rich environments of C. meneghiniana conflicts the findings mentioned earlier.
Morphology
The size of Cyclotella varies by species. C. atomus has a diameter of 5-7 μm, whereas C. quillensis can have a diameter up to 24-54 μm.[11] The most studied species of the genus, C. meneghiniana, has a diameter of 6-18 μm. Like all other diatoms, Cyclotella spp. have transparent cell walls. They form biosilica shells using dissolved silicon and carbon acquired from various carbon partitioning pathways.
Other materials Cyclotella spp. use for cell wall biosynthesis are semiconductor metal oxides and extracellular fibers made of chitin. The primary allomorph of chitin that is found most often in diatoms is α-chitin, but Cyclotella and Thalassiosira contain the β-chitin allomorph. Poly N-acetyl glucosamine chains are oriented in a parallel manner and contain intermolecular hydrogen bonds.
The bond chains and hydrogen bonds between molecules form a
Diatoms are unique in the sense that they have valves, created by the two halves of a diatom's test. Cyclotella spp. are no exception, as they form the upper and lower portions of the wall. The girdle bands that support the valves are thin strips of silica and ultimately circumscribe the cell. Each valve has two central tubes traversing its surface, meeting in the middle at the central nodule. The morphology of the Cyclotella cell wall and its valves are important traits that distinguish species from each other. Each species has tangentially undulated valves all throughout their cell wall, regardless of their length, width, and concentration.[13] Frustules contain areolas, that is orifices that mediate the passage of nutrients and exudates across the cell wall for sustenance. The characteristics of these areolas are thought to cause differences in mechanical strength and metabolism among different cells.[14]
Like other monoraphid diatoms, Cyclotella frustules can be characterized as heterovalvar. The cell wall and cell membrane are what are known to this point as what distinguishes Cyclotella from other diatom genera. The cytoplasmic components are assumed to be similar to what other diatoms have. In C. meneghiniana, there are granules scattered and attached at the chromatophore all throughout the cytoplasm. The genus is photosynthetic like all other diatoms, so all species contain one or many pyrenoids traversed by a thylakoid membrane and a chloroplast within the endoplasmic reticulum.
Life cycle
Cyclotella meneghiniana splits in half during asexual reproduction. The halves are separated by the distinction between the two valves for each cell. Each of the two offspring that arise as a result of cell division have one of the two valves from the parent cell. During the separation of the parent cell, the cytoplasm forms the two offspring valves that will end up complementing the inherited parent valves in the offspring once reproduction is complete.
The offspring valves are formed within a silica deposition vesicle that gradually grows larger and separates into two different offspring valves. The parent valves become a template for the offspring valves being formed, with patterns of striae and the central cell area also being inherited. However, perfect
Sexual reproduction occurs with gametes being formed upon reaching the threshold. During the process of meiosis, male Cyclotella cells release sperm and the female Cyclotella cells develop and egg from within the two valves. Following fertilization of the egg, a zygote is formed from the union of the two gametes. The zygote then develops into an auxophore (2n). Once sexual reproduction is complete, the diameter of the offspring is larger and beyond the threshold once again, allowing for the production of another few hundred generations through the asexual division of auxophores.
Biochemistry
Despite there being very little known about the internal morphology of Cyclotella, there have been a sizable number of studies done on the genus' molecular biology and genome. C. cryptica has been identified to be an oleaginous diatom, with a great deal of triacylglycerol. Its genome has been identified to contain many methylated repetitive sequences, which are supposed to function as a way of limiting the occurrences of DNA transposition. C. cryptica was discovered to have a very efficient lipid metabolism, which is needed for its high triacylglycerol production.[16]
Another study conducted in 1992 indicates that C. meninghiana has the largest genome and abundance of sequence repeats of any diatom species up to this specific study.
Fossil records
This section may require cleanup to meet Wikipedia's quality standards. The specific problem is: References 20 and 21 were not found during cleanup. Such citations need to be found and added. (May 2020) |
Fossils of Cyclotella are not commonly discovered, however there have been a few species found fossilized in freshwater ecosystems. Fossil assemblages have been found in glacial and interglacial segments. Regarding
A sample of C. distinguenda was found at the Agios Floros fen, in Southwest Peloponnese, Greece. The fossilized sample was dated to 5700 to 5300 years ago. Support for the recognition of a new diatom species, C. paradistinguenda, was proposed after looking through the sample of C. distinguenda (20). C. paradistinguenda was dated back to 4600 years ago. Distinctions between the two species can also be described in the differences in stratigraphic distributions between the two, as C. paradistinguenda was found in an upper organic sequence of the sample compared to C. distinguenda (20).
Another sample of Cyclotella was found at Lake Petén-Itzá, lowland Guatemala. The newfound diatom species were found fossilized morphologically distinct from other Cyclotella species (21). One of the species was named C. petenensis. The other species was named C. cassandrae, characterized by its elliptically shaped valve paired with its coarse striae. Most notably it has a scattered ring of central fultoportulae (21). Discovering fossils is not often a credible enough way to determine a new species within the phylum of diatoms, given that determining underlying mechanisms based on morphological variability is unreliable. It's best to use both morphological and paleoecological data obtained from samples- the two are often difficult to obtain just from fossils (20).
References
- ^ Kociolek, J.P.; Balasubramanian, K.; Blanco, S.; Coste, M.; Ector, L.; Liu, Y.; Kulikovskiy, M.; Lundholm, N.; Ludwig, T.; Potapova, M.; Rimet, F.; Sabbe, K.; Sala, S.; Sar, E.; Taylor, J.; Van de Vijver, B.; Wetzel, C.E.; Williams, D.M.; Witkowski, A.; Witkowski, J. (2020). "Cyclotella (F.T. Kützing) A. de Brébisson, 1838". WoRMS. World Register of Marine Species. Retrieved 11 May 2020.
- ^ a b Saros, J.E., Anderson, N.J. (2015). The ecology of the planktonic diatom Cyclotella and its implications for global environmental change studies. Biol Rev Camb Philos Soc. 90(2). 522-41.
- ISBN 978-3-443-57044-6.
- ^ a b Brébisson, [L.] A. de (1838). Considérations sur les diatomées et essai d'une classification des genres et des espèces appartenant à cette famille, par A. de Brébisson, auteur de la Flore de Normandie, etc. pp. [i], [1]-20, [4, err.]. Falaise & Paris: Brée l'Ainée Imprimeur-Libraire; Meilhac.
- ^ Håkansson H. (2002). A compilation and evaluation of species in the genera Stephanodiscus, Cyclostephanos and Cyclotella with a new genus in the family Stephanodiscaceae. Diatom Research. 17(1): 1-139.
- ^ a b Kützing, F.T. (1844). Die kieselschaligen Bacillarien oder Diatomeen. Nordhausen. 30. 1-152
- ^ a b Hasle, G.R., and E.E. Syvertsen. (1997). Marine Diatoms. In: Tomas, C.R. (Ed.) Identifying Marine Phytoplankton. Academic Press.
- ^ Schobert, B. (1974). The influence of water stress on the metabolism of diatoms I. Osmotic resistance and proline accumulation in Cyclotella meneghiniana. Zeitschrift für Pflanzenphysiologie. 74(2). 106-120.
- ^ Van de Vijver, Bart & Dessein, Steven. (2018). Cyclotella deceusteriana, a new centric diatom species (Bacillariophyta) from the sub-Antarctic Region. Phytotaxa. 333(1).
- ^ Lowe, R.L. (1975). Comparative ultrastructure of the valves of some Cyclotella species (Bacillariophyceae) Journal of Phycology. 11(4): 415-424.
- ^ Bailey, L.W. (1922). Diatoms from the Quill Lakes, Saskatchewan, and from Airdrie, Alberta.Contributions to Canadian Biology 11(1): 157-165.
- ^ LeDuff, P., & Rorrer, G. L. (2019). Formation of extracellular β-chitin nanofibers during batch cultivation of marine diatom Cyclotella sp. at silicon limitation. Journal of Applied Phycology, 31(6), 3479–3490.
- ^ Tesson, B., Hildebrand, M. (2010). Dynamics of silica cell wall morphogenesis in the diatom Cyclotella cryptica: Substructure formation and the role of microfilaments. Journal of Structural Biology. 169(1). 62-74.
- ^ a b Shirokawa, Y., Shimada, M. (2016). Cytoplasmic inheritance of parent–offspring cell structure in the clonal diatom Cyclotella meneghiniana. Proceedings of the Royal Society B. 283(1842).
- ^ Hoops, H.J., Floyd, G.L. (1979). Ultrastructure of the centric diatom, Cyclotella meneghiniana: vegetative cell and auxospore development. Phycologia. 18(4). 424-435.
- ^ Traller, J.C., Cokus, S.J., Lopez, D.A. et al. (2016). Genome and methylome of the oleaginous diatom Cyclotella cryptica reveal genetic flexibility toward a high lipid phenotype. Biotechnol Biofuels. 9(258).
- ^ Bourne, C.E.M. (1992). Chloroplast DNA structure, variation and phylogeny in closely related species of Cyclotella. ProQuest Dissertations Publishing.
- Crawford, B.J., Burke, R.D. (2004). Development of Sea Urchins, Ascidians, and Other Invertebrate Deuterostomes: Experimental Approaches. Methods in Cell Biology. 74(1). 411–441.
- Harvey, B.P., Agostini, S., Kon, K., Wada, S., Hall-Spencer, J.M. (2019). Diatoms Dominate and Alter Marine Food-Webs When CO2 Rises. Diversity. 11(12). 242.
- Round, F.E., Crawford, R.M. & Mann, D.G. (1990). The diatoms. Biology and morphology of the genera. Cambridge University Press, Cambridge.
- Spaulding, S., Edlund, M. (2008). Cyclotella. In Diatoms of North America. Retrieved April 2, 2020, from https://diatoms.org/genera/cyclotella