Rhodomonas

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Rhodomonas
Rhodomonas salina CCMP 322.jpg
Rhodomonas salina
Scientific classification
Domain:
Eukaryota
Phylum:
Cryptophyta
Class:
Cryptophyceae
Order:
Pyrenomonadales
Family:
Pyrenomonadaceae
Genus:
Rhodomonas

Karsten 1898
Type species
Rhodomonas baltica
Karsten 1898
Synonyms

Rhodomonas is a genus of cryptomonads. [1] [2] It is characterized by its red colour, the square-shaped plates of its inner periplast, its short furrow ending in a gullet, and a distinctly shaped chloroplast closely associated with its nucleomorph. [3] Historically, Rhodomonas was characterized by its red chloroplast alone, [4] but this no longer occurs as its taxonomy has become increasingly based on molecular and cellular data. [5] [6] Currently, there is some debate about the taxonomic validity of Rhodomonas as a genus and further research is needed to verify its taxonomic status. [4] [7] Rhodomonas is typically found in marine environments, although freshwater reports exist. [4] It is commonly used as a live feed for various aquaculture species. [8]

Contents

History

Discovery

Rhodomonas was first described by G. Karsten in 1898 as a “strange, swimming organism”. [4] [9] The first indication of Rhodomonas’ existence was Karsten's observation of its proliferation in a sample containing diatoms, seashells, stones, and the brown algae Sphacelaria. [4] Subsequently, Karsten established Rhodomonas baltica as the type species of the genus Rhodomonas. Karsten observed that Rhodomonas contained a red chloroplast, two posteriorly-oriented flagella originating from an anterior gullet, and a large nucleus in the middle of the cell. [4] At the time of discovery, red flagellates were previously unknown and colour was used as the identifying feature of Rhodomonas. [5] After discovery, there were multiple additions to the genus, including those by Lemmermann, Lohmann, Kylin, and Carter. [4] Zimmermann later identified Karsten's “nucleus” as the cell's pyrenoid, based on its characteristic position within the cytoplasm. [4] [5]

Taxonomic status

Presently, there is criticism against retention of Rhodomonas as a genus. Given that current taxonomy for cryptomonads is based on cellular structures and Karsten did not describe those structures in the original study, some argue that it is impossible to verify if an organism matches Karsten's original sample at an ultrastructural level. [3] [7] [10] Consequently, this raises doubt as to whether an organism that is placed in Rhodomonas truly belongs in that genus. With this perspective, there is support to transfer members of Rhodomonas to the synonymous genus Pyrenomonas. [6] [10] A countering argument is that Rhodomonas has historical priority as it was established before Pyrenomonas, and should continue to be used when referring to this genus. [4] [5] Currently, there is no definite resolution to this debate, and Rhodomonas and Pyrenomonas are used as synonyms. [4] [7] This is demonstrated in recent molecular phylogenies of cryptomonads, where it is established that Rhodomonas and Pyrenomonas are synonymous. [11] [12]

Notably, in recent phylogenies based on molecular data, the genera Rhodomonas, Rhinomonas, and Storeatula are all grouped together based on shared similarity of the examined genetic sequences. [11] [12] [13] [14] Given how closely related these genera are, there is some uncertainty as to how distinct the genus Rhodomonas is from Rhinomonas and Storeatula. [12] [15] Dimorphism has been reported in cryptomonads and is hypothesized to apply to many genera, such that some currently existing genera may actually be different morphs of one group. Applying this to the context of Rhodomonas, the genus Storeatula has been suggested to be a possible alternating morphotype for Rhinomonas and Rhodomonas due to mixing of the three groups in molecular phylogenies. [16] Further investigation is needed to better support these findings.

Habitat and ecology

Rhodomonas resides in marine environments across the globe, with some reports of freshwater species. [4] The first recorded sample of Rhodomonas was taken by G. Karsten from the Kieler Fjord of the Baltic Sea. [4] The ideal temperature range of Rhodomonas in a natural environment is reported to be 9-10°C. [17] Like many other cryptomonads, Rhodomonas species are photosynthetic. It is currently unknown if they are capable of heterotrophy. [18]

Morphology

The size of Rhodomonas species has been reported as ranging from 9-40 𝜇m, with variability between researcher reports. [4] Rhodomonas are motile cells, attributed to the presence of two flagella extending at the anterior end of the cell that allow them to swim. They are oval-shaped, with a shortened anterior end and rounded posterior end. [5]

The periplast, or cell covering, of Rhodomonas is made up of internal and external components. The external component of the periplast is made up of a coarse, intertwining fibril network that is characteristic of Rhodomonas. [4] The internal periplast component consists of small square-shaped plates arranged in longitudinal rows. To accommodate the ejectisomes of the gullet in Rhodomonas, the anterior edges of the internal periplast plates are slightly raised. [4] The posterior edges of the internal periplast plates taper towards the posterior end of the cell and attach to the cell membrane. [4] [18] The corners of the internal periplast plates are beveled. [18]

Rhodomonas cells can appear red, brown, or golden-brown in colour due to the concentration of the red pigment phycoerythrin 545 in their chloroplasts. [4] The pigment is located in the lumen surface of the thylakoid membrane within the chloroplast. [19] Within the cell, the chloroplast is found within the plastidial compartment and has close structural association with the pyrenoid. The chloroplast has two lobes and is shaped like the letter H. [3] The pyrenoid sits between the two lobes of the chloroplast, surrounded by starch. [4] The thylakoids of the chloroplast are unable to penetrate through the pyrenoidal matrix, and consequently do not cross through the pyrenoid. [18] Rhodomonas usually contains one chloroplast, although rare reports with the observation of two chloroplasts exist. [4]

The vestibulum-furrow-gullet system is a defining characteristic of Rhodomonas. [4] The vestibulum is located below the anterior apex of the cell, from which two flagella extend as is characteristic of cryptomonads. [18] The vestibulum transforms posteriorly into a furrow that closes into a gullet. The gullet is short and tubular, while the furrow can vary in length depending on the species. [4] The gullet is lined with ejectisomes that eject substances outside of the cell. [5]

The nucleomorph of Rhodomonas sits in an indentation of the periplastidial cytoplasm into the pyrenoid. [4] [18] This has also been termed as the pyrenoidal bridge. [18] This trait is shared with Rhinomonas and Storeatula, other genera that are often grouped with Rhodomonas . [11]

Rhodomonas also contains a single nucleus, located posteriorly within the cell. In the opposite direction, a contractile vacuole is located near the anterior apex of the cell. [5]

Like many other cryptomonads, Rhodomonas reproduces through asexual division. [18] It is not currently known if they are capable of sexual reproduction. [18]

Aquaculture

Rhodomonas species have been identified as a beneficial feed in aquaculture. Among other organisms, they are ideal for feeding copepods, brine shrimps, and scallop larvae. [8] [20] Their benefits as live feed for aquaculture can be attributed to their high fatty acid and protein content, which increases their nutritional content. [8] [20] It has been observed that under nitrogen starvation conditions, their nutritional content can increase. [8]

Species

The genus Rhodomonas includes the following species:

Related Research Articles

<span class="mw-page-title-main">Cryptomonad</span> Group of algae and colorless flagellates

The cryptomonads are a group of algae, most of which have plastids. They are common in freshwater, and also occur in marine and brackish habitats. Each cell is around 10–50 μm in size and flattened in shape, with an anterior groove or pocket. At the edge of the pocket there are typically two slightly unequal flagella. Some may exhibit mixotrophy. They are classified as clade Cryptomonada, which is divided into two classes: heterotrophic Goniomonadea and phototrophic Cryptophyceae. The two groups are united under three shared morphological characteristics: presence of a periplast, ejectisomes with secondary scroll, and mitochondrial cristae with flat tubules. Genetic studies as early as 1994 also supported the hypothesis that Goniomonas was sister to Cryptophyceae. A study in 2018 found strong evidence that the common ancestor of Cryptomonada was an autotrophic protist.

<i>Chlamydomonas</i> Genus of algae

Chlamydomonas is a genus of green algae consisting of about 150 species of unicellular flagellates, found in stagnant water and on damp soil, in freshwater, seawater, and even in snow as "snow algae". Chlamydomonas is used as a model organism for molecular biology, especially studies of flagellar motility and chloroplast dynamics, biogenesis, and genetics. One of the many striking features of Chlamydomonas is that it contains ion channels (channelrhodopsins) that are directly activated by light. Some regulatory systems of Chlamydomonas are more complex than their homologs in Gymnosperms, with evolutionarily related regulatory proteins being larger and containing additional domains.

Cryptomonas is the name-giving genus of the Cryptomonads established by German biologist Christian Gottfried Ehrenberg in 1831. The algae are common in freshwater habitats and brackish water worldwide and often form blooms in greater depths of lakes. The cells are usually brownish or greenish in color and are characteristic of having a slit-like furrow at the anterior. They are not known to produce any toxins. They are used to feed small zooplankton, which is the food source for small fish in fish farms. Many species of Cryptomonas can only be identified by DNA sequencing. Cryptomonas can be found in several marine ecosystems in Australia and South Korea.

<span class="mw-page-title-main">Sphaeropleales</span> Order of algae

Sphaeropleales is an order of green algae that used to be called Chlorococcales. The order includes some of the most common freshwater planktonic algae such as Scenedesmus and Pediastrum. The Sphaeropleales includes vegetatively non-motile unicellular, colonial, or filamentous taxa. They have biflagellate zoospores with flagella that are directly opposed in direction : Sphaeroplea, Atractomorpha, Neochloris, Hydrodictyon, and Pediastrum. All of these taxa have basal body core connections. Motile cells generally lack cell walls or have only a very fine layer surrounding the cell membrane. Other common characteristics include a robust vegetative cell wall, cup-shaped chloroplasts with large pyrenoids, and relatively large nuclei.

<i>Tetraselmis</i> Genus of algae

Tetraselmis is a genus of phytoplankton. Tetraselmis is a green algal genus within the order Chlorodendrales, and they are characterized by their intensely-colored green chloroplast, their flagellated cell bodies, the presence of a pyrenoid within the chloroplast, and a scale-produced thecal-wall. Species within this genus are found in both marine and freshwater ecosystems across the globe; their habitat range is mainly limited by water depth due to their photosynthetic nature. Thus, they live in diverse water environments if enough nutrients and light are available for net photosynthetic activity. Tetraselmis species have proven to be useful for both research and industry. Tetraselmis species have been studied for understanding plankton growth rates, and recently a colonial species is being used to gain an understanding of multicellularity evolution. Additionally, many species are currently being examined for their use as biofuels due to their high lipid content.

<span class="mw-page-title-main">Cryptophyceae</span> Class of single-celled organisms

The cryptophyceae are a class of algae, most of which have plastids. About 230 species are known, and they are common in freshwater, and also occur in marine and brackish habitats. Each cell is around 10–50 μm in size and flattened in shape, with an anterior groove or pocket. At the edge of the pocket there are typically two slightly unequal flagella.

<span class="mw-page-title-main">Raphidophyte</span> Group of aquatic algae

The raphidophytes, formally known as Raphidophycidae or Raphidophyceae, are a small group of eukaryotic algae that includes both marine and freshwater species. All raphidophytes are unicellular, with large cells, but no cell walls. Raphidophytes possess a pair of flagella, organised such that both originate from the same invagination. One flagellum points forwards, and is covered in hair-like mastigonemes, while the other points backwards across the cell surface, lying within a ventral groove. Raphidophytes contain numerous ellipsoid chloroplasts, which contain chlorophylls a, c1 and c2. They also make use of accessory pigments including β-carotene and diadinoxanthin. Unlike other heterokontophytes, raphidophytes do not possess the photoreceptive organelle typical of this group.

Pyrenomonas is a genus of cryptomonad.

Goniomonas is a genus of Cryptomonads and contains five species. It is a genus of single-celled eukaryotes, including both freshwater and marine species. It lacks plastids, which is very unusual among all of the Cryptophyte genera. It may reflect one of only a small number of times that the Cryptophytes evolved into freshwater habitats. Goniomonas seems to have a number of freshwater relatives which have not yet been cultured and named.

Geminigera /ˌdʒɛmɪnɪˈdʒɛɹə/ is a genus of cryptophyte from the family Geminigeraceae. Named for its unique pyrenoids, Geminigera is a genus with a single mixotrophic species. It was discovered in 1968 and is known for living in very cold temperatures such as under the Antarctic ice. While originally considered to be part of the genus Cryptomonas, the genus Geminigera was officially described in 1991 by D. R. A. Hill.

<i>Guillardia</i> Genus of single-celled organisms

Guillardia is a genus of marine biflagellate cryptomonad algae with a plastid obtained through secondary endosymbiosis of a red alga.

<i>Hemiselmis</i> Genus of single-celled organisms

Hemiselmis is a genus of cryptomonads.

Plagioselmis is a genus of cryptophytes, including the species Plagioselmis punctata.

<i>Dinophysis</i> Genus of single-celled organisms

Dinophysis is a genus of dinoflagellates common in tropical, temperate, coastal and oceanic waters. It was first described in 1839 by Christian Gottfried Ehrenberg.

<span class="mw-page-title-main">Geminigeraceae</span> Family of single-celled organisms

Geminigeraceae is a family of cryptophytes containing the five genera Geminigera, Guillardia, Hanusia, Proteomonas and Teleaulax. They are characterised by chloroplasts containing Cr-phycoerythrin 545, and an inner periplast component (IPC) comprising "a sheet or a sheet and multiple plates if diplomorphic". The nucleomorphs are never in the pyrenoid, and there is never a scalariform furrow. The cells do, however, have a long, keeled rhizostyle with lamellae (wings).

<span class="mw-page-title-main">Pyrenomonadaceae</span> Family of cryptomonads

Pyrenomonadaceae is a family of cryptomonads which includes three or four known genera. They are distinguished from other cryptomonads by their nucleomorphs being imbedded into the pyrenoid, and the presence of distinctive pigment phycoerythrin 545.

Chroomonadaceae is a family of cryptomonads first recognized by Clay et al in 1999 as including genera Chroomonas, Falcomonas, and Komma. Following a molecular phylogenic study in 2002, Hemiselmis was also placed within the Chroomonadaceae. Today, the family is generally recognized as sister to the Pyrenomonadaceae.

Cryptochrysis is a formerly recognized genus of cryptomonads first proposed by Adolf Pascher in 1911. He initially treated it as the sole genus in family Cryptochrysidaceae, but later treated it as a member of the Cryptochrysideae subfamily of Cryptomonadaceae, along with Rhodomonas, Chroomonas, and Cyanomonas. In 1967, R.W. Butcher relegated the group to a subgenus within Chroomonas.

Rhinomonas fulva is a phytoplanktonic species of cryptomonad given its current designation in 1988.

Asterochloris is a genus of green algae in the family Trebouxiophyceae. It is a common photobiont in lichen, occurring in the thalli of more than 20 lichen genera worldwide. Asterochloris is distinguishable from the morphologically similar genus Trebouxia, primarily due to its deeply lobed chloroplast, the placement of the chloroplast along the cell's periphery before the initiation of zoospore or aplanospore formation, and its tendency to primarily reproduce asexually through the production of aplanospores.

References

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  12. 1 2 3 Marin, Birger; Klingberg, Max; Melkonian, Michael (1998). "Phylogenetic Relationships among the Cryptophyta: Analyses of Nuclear-Encoded SSU rRNA Sequences Support the Monophyly of Extant Plastid-Containing Lineages". Protist. 149 (3): 265–276. doi:10.1016/S1434-4610(98)70033-1. PMID   23194638.
  13. ↑ Hoef-Emden, Kerstin; Marin, Birger; Melkonian, Michael (2002-08-01). "Nuclear and Nucleomorph SSU rDNA Phylogeny in the Cryptophyta and the Evolution of Cryptophyte Diversity". Journal of Molecular Evolution. 55 (2): 161–179. doi:10.1007/s00239-002-2313-5. ISSN   0022-2844. PMID   12107593. S2CID   25056699.
  14. ↑ Cavalier-Smith, T.; Couch, J. A.; Thorsteinsen, K. E.; Gilson, P.; Deane, J. A.; Hill, D. R. A.; Mcfadden, G. I. (1996). "Cryptomonad nuclear and nucleomorph 18S rRNA phylogeny". European Journal of Phycology. 31 (4): 315–328. doi:10.1080/09670269600651541. ISSN   0967-0262.
  15. ↑ Hoef-Emden, Kerstin; Melkonian, Michael (2003). "Revision of the Genus Cryptomonas (Cryptophyceae): a Combination of Molecular Phylogeny and Morphology Provides Insights into a Long-Hidden Dimorphism". Protist. 154 (3–4): 371–409. doi:10.1078/143446103322454130. PMID   14658496.
  16. ↑ Majaneva, Markus; Remonen, Iina; Rintala, Janne-Markus; Belevich, Ilya; Kremp, Anke; Setälä, Outi; Jokitalo, Eija; Blomster, Jaanika (2014). "Rhinomonas nottbecki n. sp. (Cryptomonadales) and Molecular Phylogeny of the Family Pyrenomonadaceae". Journal of Eukaryotic Microbiology. 61 (5): 480–492. doi:10.1111/jeu.12128. PMID   24913840. S2CID   24145879.
  17. ↑ Krasnova, E. D.; Pantyulin, A. N.; Matorin, D. N.; Todorenko, D. A.; Belevich, T. A.; Milyutina, I. A.; Voronov, D. A. (2014). "Cryptomonad alga Rhodomonas sp. (Cryptophyta, Pyrenomonadaceae) bloom in the redox zone of the basins separating from the White Sea". Microbiology. 83 (3): 270–277. doi:10.1134/S0026261714030102. ISSN   0026-2617. S2CID   17592032.
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  19. ↑ Ludwig, M; Gibbs, S P (1989-03-01). "Localization of phycoerythrin at the lumenal surface of the thylakoid membrane in Rhodomonas lens". Journal of Cell Biology. 108 (3): 875–884. doi:10.1083/jcb.108.3.875. ISSN   0021-9525. PMC   2115399 . PMID   2921285.
  20. 1 2 Oostlander, P.C.; van Houcke, J.; Wijffels, R.H.; Barbosa, M.J. (2020). "Optimization of Rhodomonas sp. under continuous cultivation for industrial applications in aquaculture". Algal Research. 47: 101889. doi: 10.1016/j.algal.2020.101889 . hdl: 11250/2731572 . S2CID   216351480.
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