Actinophryid

Last updated

Actinophryid
Actinophrys sol (phase contrast microscopy).jpg
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Clade: Diaphoretickes
Clade: SAR
Clade: Stramenopiles
Phylum: Gyrista
Subphylum: Ochrophytina
Class: Raphidomonadea
Subclass: Raphopoda
Order: Actinophryida
Hartmann 1913
Suborders & families [1]
Diversity
9 species

The actinophryids are an order of heliozoa, a polyphyletic array of stramenopiles, having a close relationship with pedinellids and Ciliophrys. They are common in fresh water and occasionally found in marine and soil habitats. Actinophryids are unicellular and roughly spherical in shape, with many axopodia that radiate outward from the cell body. Axopodia are a type of pseudopodia that are supported by hundreds of microtubules arranged in interlocking spirals and forming a needle-like internal structure or axoneme. Small granules, extrusomes, that lie under the membrane of the body and axopodia capture flagellates, ciliates and small metazoa that make contact with the arms. [2] [3]

Contents

Description

Actinophryids are largely aquatic protozoa with a spherical cell body and many needle-like axopodia. They resemble the shape of a sun due to this structure, which is the inspiration for their common name: heliozoa, or "sun-animalcules". Their bodies, without arms, range in size from a few tens of micrometers to slightly under a millimeter across. [1]

The outer region of cell body is often vacuolated. The endoplasm of actinophryids is less vacuolated than the outer layer, and a sharp boundary layer may be seen by light microscopy. [4] The organisms can be either mononucleate, with a single, well defined nucleus in the center of the cell body, or multinucleate, with 10 or more nuclei located under the outer vacuolated layer of cytoplasm. The cytoplasm of actinophryids is often granular, similar to that of Amoeba . [5]

Actinophryid cells may fuse when feeding, creating larger aggregated organisms. Fine granules that occur just under the cell membrane are used up when food vacuoles form to enclose prey. [6] Actinophryids may also form cysts when food is not readily available. A layer of siliceous plates is deposited under the cell membrane during the encystment process. [7]

Video of a contractile vacuole collapse in Actinosphaerium

Contractile vacuoles are common in these organisms, which are presumed to use them to maintain body volume by expelling fluids to compensate for the entry of water by osmosis. Contractile vacuoles are visible as clear bulges from the surface of the cell body that slowly fill then rapidly deflate, expelling their contents into the environment.

Axopodia

Cross-section of the double spiral microtubule structure in an axopod Axopodium Mikrotubuli.jpg
Cross-section of the double spiral microtubule structure in an axopod

The most distinctive characteristic of the actinophryids is their axopodia. These axopodia consist of a central, rigid rod which is coated in a thin layer of ectoplasm. In Actinophrys the axonemes end on the surface of the central nucleus, and in the multicellular Actinosphaerium they end at or near nuclei. [5] The axonemes are composed of microtubules arranged in a double spiral pattern characteristic of the order. [8] Due to their long, parallel construction, these microtubules demonstrate strong birefringence. [9] [10]

These axopodia are used for prey capture, in movement, cell fusion and perhaps division. [2] [3] They are stiff but may flex especially near their tips, [4] and are highly dynamic, undergoing frequent construction and destruction. When used to collect prey items, two methods of capture have been noted, termed axopodial flow and rapid axopodial contraction. [2] Axopodial flow involves the slow movement of a prey item along the surface of the axopod as the ectoplasm itself moves, while rapid axopodial contraction involves the collapse of the axoneme's microtubule structure. [10] This behavior has been documented in many species, including Actinosphaerium nucleofilum, Actinophrys sol, and Raphidiophrys contractilis . [10] [11] [12] The rapid axopodial contraction occurs at high speed, often in excess of 5mm/s or tens of body lengths per second. [13]

The axopodial contractions have been shown to be highly sensitive to environmental factors such as temperature and pressure [9] [14] as well as chemical signals like Ca2+ and colchicine. [11] [15]

Reproduction

Actinophrys undergoing multiple plasmotomy Heliozoen.jpg
Actinophrys undergoing multiple plasmotomy

Reproduction in actinophryids generally takes place via fission, where one parent cell divides into two or more daughter cells. For multinucleate heliozoa, this process is plasmotomic as the nuclei are not duplicated prior to division. [4] It has been observed that reproduction appears to be a response to food scarcity, with an increased number of divisions following the removal of food and larger organisms during times of food excess. [16]

Actinophryids also undergo autogamy during times of food scarcity. This is better described as genetic reorganization than reproduction, as the number of individuals produced is the same as the initial number. Nonetheless, it serves as a way to increase genetic diversity within an individual which may improve the likelihood of expressing favorable genetic traits. [17]

Plastogamy has also been extensively documented in actinophryids, especially in multinucleate ones. Actinosphaerium were observed to combine freely without the combination of nuclei, and this process sometimes resulted in more or less individuals than originally combined. This process is not caused merely by contact between two individuals but can be caused by damage to the cell body. [16]

Cyst function and formation

Under unfavourable conditions, some species will form a cyst. This is often the product of autogamy, in which case the cysts produced are zygotes. [17] Cells undergoing this process withdraw their axopodia, adhere to the substrate, and take on an opaque and grayish appearance. [18] This cyst then divides until only uninucleate cells remain. The cyst wall is thickly layered 7–8 times and includes gelatinous layers, layers of silica plates, and iron. [19]

Taxonomy

Originally placed in Heliozoa (Sarcodina), the actinophryids are now understood to be part of the stramenopiles. They are unrelated to centrohelid and desmothoracid heliozoa with which they had been previously classified.

There are several genera included within this classification. [20] Actinophrys are smaller and have a single, central nucleus. [11] Most have a cell body 40–50 micrometer in diameter with axopods around 100 μm in length, though this varies significantly. Actinosphaerium are several times larger, from 200 to 1000 μm in diameter, with many nuclei [11] and are found exclusively in fresh water. [21] A third genus, Camptonema, has a debated status. It has been observed once and was treated as a junior subjective synonym of Actinosphaerium by Mikrjukov & Patterson in 2001, [20] but as a valid genus by Cavalier-Smith & Scoble (2013). [1] Heliorapha is a further debated taxon, it being a new generic vehicle for the species azurina that was initially assigned to the genus Ciliophrys. [1]

Classification

According to the latest review of actinophryid classifications, they are organized into two suborders, three families and three genera. [1] [20]

Related Research Articles

<span class="mw-page-title-main">Stramenopile</span> Clade of eukaryotes

The Stramenopiles, also called Heterokonts, are a clade of organisms distinguished by the presence of stiff tripartite external hairs. In most species, the hairs are attached to flagella, in some they are attached to other areas of the cellular surface, and in some they have been secondarily lost. Stramenopiles represent one of the three major clades in the SAR supergroup, along with Alveolata and Rhizaria.

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

The centrohelids or centroheliozoa are a large group of heliozoan protists. They include both mobile and sessile forms, found in freshwater and marine environments, especially at some depth.

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

Pedinellales is a group of single-celled algae found in both marine environments and freshwater.

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

The axodines are a group of unicellular stramenopiles that includes silicoflagellate and rhizochromulinid algae, actinomonad heterotrophic flagellates and actinophryid heliozoa. Alternative classifications treat the dictyochophytes as heterokont algae, or as Chrysophyceae. Other overlapping taxonomic concepts include the Actinochrysophyceae, Actinochrysea or Dictyochophyceae sensu lato. The grouping was proposed on the basis of ultrastructural similarities, and is consistent with subsequent molecular comparisons.

<span class="mw-page-title-main">Heliozoa</span> Phylum of protists with spherical bodies

Heliozoa, commonly known as sun-animalcules, are microbial eukaryotes (protists) with stiff arms (axopodia) radiating from their spherical bodies, which are responsible for their common name. The axopodia are microtubule-supported projections from the amoeboid cell body, and are variously used for capturing food, sensation, movement, and attachment. They are similar to Radiolaria, but they are distinguished from them by lacking central capsules and other complex skeletal elements, although some produce simple scales and spines. They may be found in both freshwater and marine environments.

<i>Actinophrys</i> Family of heliozoan protists

Actinophrys is a genus of heliozoa, amoeboid unicellular organisms with many axopodial filaments that radiate out of their cell. It contains one of the most common heliozoan species, Actinophrys sol. It is classified within the monotypic family Actinophryidae.

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

Colpodella is a genus of alveolates comprising 5 species, and two further possible species: They share all the synapomorphies of apicomplexans, but are free-living, rather than parasitic. Many members of this genus were previously assigned to a different genus - Spiromonas.

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

Nassula is a genus of unicellular ciliates, belonging to the class Nassophorea. Like other members of the class, Nassula possesses a basket-like feeding apparatus made up of cytopharyngeal rods (nematodesmata), which are themselves composed of closely packed microtubules. Nassula use this structure to ingest filamentous cyanobacteria, drawing individual strands of blue-green algae through the cytopharynx and into the body of the cell, where they are digested. As the algae are broken down, they can take on a variety of bright colours, which give Nassula a distinctive, variegated appearance under the microscope.

<i>Actinosphaerium</i> Genus of heliozoan protists

Actinosphaerium is a genus of heliozoa, amoeboid unicellular organisms with many axopodial filaments that radiate out of their cell. It is classified within the monotypic family Actinosphaeriidae and suborder Actinosphaerina. Species of Actinophrys are distinguished by their large number of nuclei in each cell. Their axopodia sometimes terminate on the surface of nuclei. Vacuoles are abundant in the periphery of the cytoplasm.

<i>Mastigamoeba</i> Genus of flagellar amoeboids

Mastigamoeba is a genus of pelobionts, and treated by some as members of the Archamoebae group of protists. Mastigamoeba are characterized as anaerobic, amitochondriate organisms that are polymorphic. Their dominant life cycle stage is as an amoeboid flagellate. Species are typically free living, though endobiotic species have been described.

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

Raphidiophrys is a genus of centrohelid with radiating axopodia. R. intermedia is found in the bottom sludge of freshwater bodies in Canada, Chile, Argentina, Australia, New Zealand, Malaysia, Russia, and central Europe. Raphidiophrys have bipartite scales are a defining characteristic among species. Differences in type and size of scales are used to differentiate amongst the members of this genus. The genus Raphidiophrys was discovered in 1867 by W. Archer. Raphidiophrys is one of very few centrohelids in which dimorphism has been shown.

<i>Raphidiophrys contractilis</i> Species of single-celled organism

Raphidiophrys contractilis is a species of freshwater centrohelid.

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

Reticulomyxa is a monospecific genus of freshwater foraminiferans. The type species is the unicellular Reticulomyxa filosa. It is found in freshwater environments as well as moist environments, like decomposing matter and damp soils. The heterotrophic naked foraminiferan can feed on microbes as well has larger organisms and is able to be sustained in culture by supplemented nutrients such as wheat germ and oats. The large, multinucleate foraminferan is characteristic for its lack of test and named for the network of connecting pseudopodia surrounding its central body mass. The organism has unique bidirectional cytoplasmic streaming throughout the anastomosing pseudopodia that is some of the fastest reported organelle transport observed. Reticulomyxa was first described in 1949 and is commonly used as a model organism for the unique transport of organelles throughout the cytoplasm of pseudopodia by cytoskeletal mechanisms. Only asexual reproduction of this genus has been observed in culture, but the genome possesses genes related to meiosis suggesting it is capable of sexually reproductive life stages.

<span class="mw-page-title-main">Raphidomonadea</span> Class of algae and protozoa

Raphidomonadea is a class of Stramenopiles containing both photosynthetic and phagotrophic protists. The phagotrophic groups are known as Raphopoda, and comprise actinophryid heliozoa and the marine genus Commation. The photosynthetic groups are known as the raphidophyte algae. Their relationship was elucidated through phylogenetic analyses.

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

Vampyrella is a genus of amoebae belonging to the vampyrellid cercozoans usually ranging from 30-60 µm. Members of the genus alternate between two life stages: a free-living trophozoite stage and a cyst stage in which mitosis occurs. This taxon has received a great deal of attention due to their peculiar feeding behaviour of perforating the cell wall of algal cells and drawing out the contents for nourishment.

<span class="mw-page-title-main">Ultrastructural identity</span>

Ultrastructural identity is a concept in biology. It asserts that evolutionary lineages of eukaryotes in general and protists in particular can be distinguished by complements and arrangements of cellular organelles. These ultrastructural components can be visualized by electron microscopy.

Tetrahelia is a genus of four-ciliated protists belonging to the Endohelea, a group of heterotrophic eukaryotes previously considered heliozoa. It is the only genus in the family Tetraheliidae and order Axomonadida. It is a monotypic genus, containing the sole species Tetrahelia pterbica, previously classified as Tetradimorpha.

Yogsothoth is a genus of centrohelid protists, distinguished by the shape and arrangement of their external scales as well as their colonial life strategy. It was described in November 2018 by Shɨshkin and Zlatogursky, and is part of a newly described clade of centrohelids, determined as such by analysis of molecular data.

Heliorapha is a genus of heliozoan protists, amoeboid eukaryotes with stiff axopodia radiating from their cells. It contains one species, Heliorapha azurina. It is classified within a monotypic family Helioraphidae inside the actinophryids, a group of heliozoa that belong to the Ochrophyta along with other protists such as diatoms and brown algae.

Commation eposianum is a species of heterotrophic protists discovered in 1993 in Antarctic waters. It is one of two species in the Commatiida, an order of stramenopiles closely related to actinophryids, a group of heliozoan protists, and to raphidophytes, a group of algae.

References

  1. 1 2 3 4 5 Cavalier-Smith, T; Scoble, JM (August 2013). "Phylogeny of Heterokonta: Incisomonas marina, a uniciliate gliding opalozoan related to Solenicola (Nanomonadea), and evidence that Actinophryida evolved from raphidophytes". European Journal of Protistology. 49 (3): 328–53. doi:10.1016/j.ejop.2012.09.002. PMID   23219323.
  2. 1 2 3 Suzaki, T.; Shigenaka, Y.; Watanabe, S.; Toyohara, A. (1980). "Food capture and ingestion in the large heliozoan, Echinosphaerium nucleofilum". Journal of Cell Science. 42: 61–79. doi:10.1242/jcs.42.1.61. ISSN   0021-9533. PMID   7400244.
  3. 1 2 Ando, Motonori; Shigenaka, Yoshinobu (1989). "Structure and function of the cytoskeleton in heliozoa: I. Mechanism of rapid axopodial contraction in Echinosphaerium". Cell Motility and the Cytoskeleton. 14 (2): 288–301. doi:10.1002/cm.970140214.
  4. 1 2 3 Barrett, J. (August 1958). "Some Observations on Actinosphaerium nucleofilum n. sp., a New Fresh Water Actinophryid". The Journal of Protozoology. 5 (3): 205–209. doi:10.1111/j.1550-7408.1958.tb02553.x.
  5. 1 2 Anderson, E.; Beams, H. W. (May 1960). "The Fine Structure of the Heliozoan, Actinosphaerium nucleofilum". The Journal of Protozoology. 7 (2): 190–199. doi:10.1111/j.1550-7408.1960.tb00729.x.
  6. ↑ Patterson, D. J. & Hausmann, K. 1981. Feeding by Actinophrys sol (Protista, Heliozoa): I. Light microscopy. Microbios 31: 39–55.
  7. ↑ Patterson, D.J. 1979. On the organization and classification of the protozoon Actinophrys sol Ehrenberg, 1830. Microbios 26: 165–208.
  8. ↑ Gast, R.J. (2017). "Centrohelida and Other Heliozoan-like Protists". In Archibald, J.; Simpson, A.; Slamovits, C.; Margulis, L.; Melkonian, M.; Chapman, D.; Corliss, J. (eds.). Handbook of the Protists. Cham, Switzerland: Springer International. pp. 1–17. doi:10.1007/978-3-319-32669-6_28-1. ISBN   978-3-319-32669-6.
  9. 1 2 Tilney, L.; Porter, K. (July 1967). "Studies on the microtubules in heliozoa II. The effect of low temperature on these structures in the formation and maintenance of the axopodia". Journal of Cell Biology. 34 (1): 327–343. doi:10.1083/jcb.34.1.327. PMC   2107222 . PMID   6033539.
  10. 1 2 3 Suzaki, Toshinobu; Ando, Motonori; Inai, Yoko; Shigenaka, Yoshinobu (November 1994). "Structure and function of the cytoskeleton in heliozoa". European Journal of Protistology. 30 (4): 404–413. doi:10.1016/S0932-4739(11)80215-4.
  11. 1 2 3 4 Kinoshita, E; Shigenaka, Y; Suzaki, T (2001). "The ultrastructure of contractile tubules in the heliozoon Actinophrys sol and their possible involvement in rapid axopodial contraction". The Journal of Eukaryotic Microbiology. 48 (5): 519–26. doi:10.1111/j.1550-7408.2001.tb00187.x. PMID   11596916.
  12. ↑ Kinoshita, Eiji; Suzaki, Toshinobu; Shigenaka, Yoshinobu; Sugiyama, Masanori (May 1995). "Ultrastructure and Rapid Axopodial Contraction of a Heliozoa, Raphidiophrys contractilis sp. nov". The Journal of Eukaryotic Microbiology. 42 (3): 283–288. doi:10.1111/j.1550-7408.1995.tb01581.x.
  13. ↑ Shigenaka, Y.; Yano, K.; Suzaki, T. (1982). "Shigenaka, Y., Yano, K., Yogosawa, R. and Suzaki, T., 1982. Rapid contraction of the microtubule-containing axopodia in a large heliozoan Echinosphaerium". Biological functions of microtubules and related structures. Tokyo: Academic Press. pp. 105–114.
  14. ↑ Tilney, Lewis G.; Byers, Breck (1 October 1969). "Studies on the Microtubules in Heliozoa V. Factors Controlling the Organization of Microtubules in the Axonemal Pattern in Echinosphaerium nucleofilum". The Journal of Cell Biology. 43 (1): 148–165. doi:10.1083/jcb.43.1.148. ISSN   0021-9525. PMC   2107851 . PMID   5824062.
  15. ↑ Tilney, L. (December 1968). "Studies on the microtubules in heliozoa. IV. The effect of colchicine on the formation and maintenance of the axopodia and the redevelopment of pattern in Actinosphaerium nucleofilum (Barrett)". Journal of Cell Science. 3 (4): 549–62. doi:10.1242/jcs.3.4.549. PMID   5707852.
  16. 1 2 Johnson, Herbert P. (April 1894). "The plastogamy of actinosphaerium". Journal of Morphology. 9 (2): 269–276. doi:10.1002/jmor.1050090206. hdl: 2027/hvd.32044107306375 .
  17. 1 2 Grell, Karl Gottlieb (2013). Protozoology. Berlin, Heidelberg: Springer Berlin Heidelberg. pp. 178–181. ISBN   9783642619588.
  18. ↑ MacKinnon, D. L. (1906). "A few Observations on the Encystation of Actinosphaerium eichhorni under different conditions of Temperature" (PDF). Quarterly Journal of Microscopical Science. 52: 407–422. Archived (PDF) from the original on 2022-10-09. Retrieved 2 January 2018.
  19. ↑ Patterson, D.; Thompson, D. (May 1981). "Structure and Elemental Composition of the Cyst Wall of Echinosphaerium nucleofilum Barrett (Heliozoea, Actinophryida)". The Journal of Protozoology. 28 (2): 188–192. doi:10.1111/j.1550-7408.1981.tb02831.x.
  20. 1 2 3 Mikrjukov, Kirill A.; Patterson, David J. (2001). "Taxonomy and phylogeny of Heliozoa. III. Actinophryids" (PDF). Acta Protozoologica. 40: 3–25.
  21. ↑ "Actinosphaerium eichhornii". Microworld. 2019-02-28. Retrieved 2020-01-29.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.