Labyrinthula

Last updated

Labyrinthula
Scientific classification
Domain:
Eukaryota
(unranked):
SAR
Superphylum:
Heterokonta
Phylum:
Bigyra
Class:
Labyrinthulae
Order:
Labyrinthulida
Family:
Labyrinthulidae
Genus:
Labyrinthula

The genus Labyrinthula is part of the protist group Labyrinthulomycetes and contains thirteen species. The major feature of this genus is the formation of an ectoplasmic net secreted by specialized organelles called bothrosomes which surrounds the colony, which is also used by Labyrinthula for moving. The protist reproduces by zoosporulation as it sets some flagellated spores free from a sporangium. One of the flagella of the zoospores has stiff tripartite hairs (mastigonemes) - the defining characteristic of the stramenopiles.

Contents

The interest in Labyrinthula arose as it has been identified as the cause of the "wasting disease", which led to the death of more than 90% of the seagrass population of the North Atlantic coast in the early 1930s. [1]

Etymology

A labyrinth is a synonym of a maze, reflecting the ectoplasmic net, which gives the protist a net-like shape which resembles a maze. The word comes from Ancient Greek λαβύρινθος (labúrinthos, “maze”).

History of Knowledge

Cienkowski was the first person who published on Labyrinthula in 1867. [2] He studied primarily the morphology, and he identified two species: Labyrinthula vitelli and Labyrinthula macrocystis.

In 1967, Pokorny published the first review over Labyrinthula and counted ten marine species, two freshwater species and one terrestrial species. [3]

Before being considered as protists and Stramenopiles, [4] Labyrinthula had been classified in the Mycetozoa, [5] the slime molds [6] and the Rhizopodia. [7]

Interest in Labyrinthula started when it was defined as the cause of the "wasting disease". An epidemic happened in the 1930s in the North American and European coasts, killing over 90% of the seagrass ( Zostera marina ) population. [1] The first description of similar symptoms in terrestrial grasses happened in 1995 in California. The target organism is turfgrass and the pathogen identified by the Koch's postulates is L. terrestris. [8] Both seagrass and turfgrass can be infected by organisms of the Labyrinthula genera, but from different species, one marine and one terrestrial one, respectively.

Habitat and Ecology

The habitat of Labyrinthula is very diverse, they are found in marine and freshwater environments as well as in terrestrial environments all over the world. Labyrinthula have been found to live as pathogens, commensals or mutualists on several host organisms. One example is the endosymbiont Labyrinthula sp. inside Thecamoeba hilla, which seem to live as mutualists symbionts. [9]

Description of the Organism

Morphology and Anatomy

The morphology of a single cell of Labyrinthula is not unique and varies a lot between the different species. The cells can be spindle-shaped like L. macrocystis, spherical or ovoid to name only a few examples. The spindle shape is due to the microtubules of the cytoskeleton. [10] There is no mean size of one cell, because of the diversity between the species. An approximation can still be made at 8-30 γm in length and 1.5-8 γm in width. [3] The general morphology of the cell contain one central nucleus, the smooth endoplasmatic reticulum, mitochondria with tubular cristae, numerous lipid-composed granules and two large Golgi complexes. [9] Labyrinthula are non-photosynthetic and are usually translucent white, but some yellow strains have been observed. [11]

Ectoplasmic Net

The defining characteristic of the genera Labyrinthula is the formation of an ectoplasmic net around the cells and embedding the whole colony. The ectoplasmic net is secreted and attached to the cell by specialized organelles called segenetosome or bothrosomes. A bothrosome is an electron-opaque organelle, which prevents the leaking of the organelles into the net. The etymology of "bothrosome" and "sagenetosome" originated from bothros : hole and soma: body, as well as from sagena: net, genetes: ancestor and soma: body respectively. The net is composed of secreted ectoplasm and is delimited by a plasma membrane. It lacks a cell wall and contains no organelles. By forming long filaments, the ectoplasmic net allows the colony to attach to surfaces and it secretes digestive enzymes for absorptive nutrition. These enzymes can be surface-bound or secreted into the medium to help the digestion of organic substances. Individual cells use the ectoplasmic net for movement by gliding inside it. They move in all directions, but they tend to go towards the periphery of the ectoplasmic net to enlarge the net and thus increase its surface area. [12] [13]

Spindle-shaped cells of Labyrinthula within an ectoplasmic net. Cells are about 15 mm long. Protist labyrinthula 1000 Maple Ferryman.jpg
Spindle-shaped cells of Labyrinthula within an ectoplasmic net. Cells are about 15 μm long.

Cell Wall

Despite the lack of cell wall of the ectoplasmic net, each individual cell is surrounded by a cell wall located close to the cell membrane and composed of a single layer of Golgi-derived circular scales, which overlap over a few nanometers, but do not fuse. The main components of the cell wall are fucose or galactose-derived substances. [12]

Life Cycle

Por: Ximena Gaytan Mosqueda Ciclo de vida Labyrinthula macrocystis.jpg
Por: Ximena Gaytan Mosqueda

The reproduction of Labyrinthula occurs by zoosporulation, no sexual reproductive cells or structures have been identified yet. First, vegetative cells aggregate inside the ectoplasmic net and form yellow to orange networks in different areas of the net. The cells in these aggregates are compressed together and the boundaries blur, which leads to a plasmodium-like appearance. The vegetative cells then round up and enlarge to form a presporangium. A presporangium is delimited by an envelope of scales, which build a rather thick membrane. The presporangium is further divided into sporangia, and in some species into a sori, [14] until each of them contain eight zoospores. The zoospores are released directly into the ectoplasmic net, where they swim away from the sporangium. [15]

The morphology of the zoospore is similar to a "standard" stramenopile cell. Zoospores contain an eyespot and two flagella. Only the anterior flagellum is covered with mastigonemes and the posterior flagellum propels the cell through the ectoplasmic net. Both flagella are inserted laterally and medially. After about 24 hours, the zoospores lose their flagella and round up to finally differentiate into vegetative spindle cells. [15] [14] Vegetative cells stop gliding through the net in older cultures or under bad conditions. Only few of the older cells autolyze, but most of them round up. [16]

Vegetative cells multiply mostly by mitosis. Some features of their binary fission are the de novo synthesis of the bothrosome and the cytokinesis, that occurs by vesicle accumulation and fusion. [10]

Practical Importance

Labyrinthula have awoken the interest of scientists by being the cause of the "wasting disease" of the seagrass on the North American and European coasts in the 1930s. Since then, several pathogenic species have been identified which mostly live in marine water.

Studies testing the virulence of the protist in seagrasses showed a low virulence of Labyrinthula. The protist often lives inside the multicellular organism, but does not initiate any pathogenic event. Pathogenesis may be triggered by biotic or abiotic stress of the higher organism, like a large increase in temperature or a decrease in light exposure for example. [17]

The most famous parasitic symbiont is L. zosterae, which colonizes marine seagrasses referring to the event mentioned above. Typical features of the "wasting disease" are a discolouration of the leaves, due to the destruction of the chloroplasts in epidermis, mesophyll and lesion formation. The second stage is the occurrence of brown and black blotches. [13] The infection and the following consequences are a concern, because of the ecological and economical importance of the seagrass in the marine environment. [18] The infection is transferred by direct contact between the target organisms and correlates with the salinity of the water. [18]

Another parasitic Labyrinthula is L. terrestris, which is a terrestrial parasite of turf grasses. It has been identified by the Koch's postulates as responsible for the "rapid blight" killing infected turf grasses. [8] Some other symbiont hosts of Labyrinthula are Chaetomorpha media, a green algae [19] and Thecamoeba hilla where they live as mutualistic symbiont. [9]

List of Species

SpeciesDiscovererYear
L. macrocystis [2] CIenkowski1867
L. vitellina [2] Cienkowski1867
L. cienkowskii [5] Zopf1892
L. zopfii Dangeard1910
L. chattonii [20] Dangeard1932
L. valkanovii [21] Karling1944
L. algeriensis [22] Hollande & Enjumet1955
L. roscoffensis [23] Chadefaud1956
L. spp / L. zosterae Watson1957
L.sp Type LXWatson1957
L. sp Type SELXWatson1957
L. coenocystis [24] Schmoller1960
L. terrestris [8] Bigelow2005

Related Research Articles

<span class="mw-page-title-main">Actinophryid</span> Order of heliozoan protists

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.

<span class="mw-page-title-main">Flagellate</span> Group of protists with at least one whip-like appendage

A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word flagellate also describes a particular construction characteristic of many prokaryotes and eukaryotes and their means of motion. The term presently does not imply any specific relationship or classification of the organisms that possess flagella. However, several derivations of the term "flagellate" are more formally characterized.

<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">Labyrinthulomycetes</span> Class of protists that produce a filamentous network

Labyrinthulomycetes (ICBN) or Labyrinthulea (ICZN) is a class of protists that produce a network of filaments or tubes, which serve as tracks for the cells to glide along and absorb nutrients for them. The two main groups are the labyrinthulids and thraustochytrids. They are mostly marine, commonly found as parasites on algae and seagrasses or as decomposers on dead plant material. They also include some parasites of marine invertebrates and mixotrophic species that live in a symbiotic relationship with zoochlorella.

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

Pelomyxa is a genus of giant flagellar amoebae, usually 500–800 μm but occasionally up to 5 mm in length, found in anaerobic or microaerobic bottom sediments of stagnant freshwater ponds or slow-moving streams.

<span class="mw-page-title-main">Lobosa</span> Phylum of protozoans

Lobosa is a taxonomic group of amoebae in the phylum Amoebozoa. Most lobosans possess broad, bluntly rounded pseudopods, although one genus in the group, the recently discovered Sapocribrum, has slender and threadlike (filose) pseudopodia. In current classification schemes, Lobosa is a subphylum, composed mainly of amoebae that have lobose pseudopods but lack cilia or flagella.

<span class="mw-page-title-main">Discosea</span> Class of amoebae

Discosea is a class of Amoebozoa, consisting of naked amoebae with a flattened, discoid body shape. Members of the group do not produce tubular or subcylindrical pseudopodia, like amoebae of the class Tubulinea. When a discosean is in motion, a transparent layer called hyaloplasm forms at the leading edge of the cell. In some discoseans, short "subpseudopodia" may be extended from this hyaloplasm, but the granular contents of the cell do not flow into these, as in true pseudopodia. Discosean amoebae lack hard shells, but some, like Cochliopodium and Korotnevella secrete intricate organic scales which may cover the upper (dorsal) surface of the cell. No species have flagella or flagellated stages of life.

<i>Trichonympha</i> Genus of flagellated protists

Trichonympha is a genus of single-celled, anaerobic parabasalids of the order Hypermastigia that is found exclusively in the hindgut of lower termites and wood roaches. Trichonympha’s bell shape and thousands of flagella make it an easily recognizable cell. The symbiosis between lower termites/wood roaches and Trichonympha is highly beneficial to both parties: Trichonympha helps its host digest cellulose and in return receives a constant supply of food and shelter. Trichonympha also has a variety of bacterial symbionts that are involved in sugar metabolism and nitrogen fixation.

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

Sagenista is a group of heterokonts containing the labyrinthulids and Eogyrea, a class of yet uncultured protists. Originally, it contained the Labyrinthulids and bicosoecids. The bicosoecids have been removed, and Eogyrea were added, in order to make the group monophyletic.

<span class="mw-page-title-main">Protozoan infection</span> Parasitic disease caused by a protozoan

Protozoan infections are parasitic diseases caused by organisms formerly classified in the kingdom Protozoa. These organisms are now classified in the supergroups Excavata, Amoebozoa, Harosa, and Archaeplastida. They are usually contracted by either an insect vector or by contact with an infected substance or surface.

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

Bigyra is a phylum of microscopic eukaryotes that are found at the base of the Stramenopiles clade. It includes three well-known heterotrophic groups Bicosoecida, Opalinata and Labyrinthulomycetes, as well as several small clades initially discovered through environmental DNA samples: Nanomonadea, Placididea, Opalomonadea and Eogyrea. The classification of Bigyra has changed several times since its origin, and its monophyly remains unresolved.

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

Proteromonas is a genus of single-celled biflagellated microbial eukaryotes belonging to the Superphylum Stramenopiles which are characterized by the presence of tripartite, hair-like structures on the anteriorly-directed larger of the two flagella. Proteromonas on the other hand are notable by having tripartite hairs called somatonemes not on the flagella but on the posterior of the cell. Proteromonas are closely related to Karotomorpha and Blastocystis, which belong to the Opalines group.

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

Parvilucifera is a genus of marine alveolates that behave as endoparasites of dinoflagellates. It was described in 1999 by biologists Fredrik Norén and Øjvind Moestrup, who identified the genus among collections of Dinophysis dinoflagellates off the coast of Sweden. Initially mistaken for products of sexual reproduction, the round bodies found within these collections were eventually recognized as sporangia, spherical structures that generate zoospores of a parasitic protist. This organism was later identified as P. infectans, the type species. The examination of this organism and its close genetic relationship to Perkinsus led to the creation of the Perkinsozoa phylum within the Alveolata group.

<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.

<i>Plasmodiophora bicaudata</i> Parasitic species of protist affecting plants

Plasmodiophora bicaudata is a marine pathogen, an obligate parasite of seagrass of the genus Zostera and the causal agent of wasting disease in the genus. These marine plants grow in fine sediment in shallow seas and the pathogen seems to have a worldwide distribution.

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

The genus Aplanochytrium is part of the class Labyrinthulomycetes. It is a sister genus of Labyrinthula and thraustochytrids. The major characteristic of all three genera is the production of an extension of the plasma membrane and the ectoplasm called the ectoplasmic net, but its use is different in each genera. Aplanochytrium cells are not embedded in the ectoplasmic net but can move by gliding on the ectoplasmic threads.

<span class="mw-page-title-main">Thraustochytrids</span> Order of eukaryotes

Thraustochytrids are single-celled saprotrophic eukaryotes (decomposers) that are widely distributed in marine ecosystems, and which secrete enzymes including, but not limited to amylases, proteases, phosphatases. They are most abundant in regions with high amounts of detritus and decaying plant material. They play an important ecological role in mangroves, where they aid in nutrient cycling by decomposing decaying matter. Additionally, they contribute significantly to the synthesis of omega-3 polyunsaturated fatty acids (PUFAs): docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), which are essential fatty acids for the growth and reproduction of crustaceans. Thraustochytrids are members of the class Labyrinthulea, a group of protists that had previously been incorrectly categorized as fungi due to their similar appearance and lifestyle. With the advent of DNA sequencing technology, labyrinthulomycetes were appropriately placed with other stramenopiles and subsequently categorized as a group of Labyrinthulomycetes.

Monocercomonas is a Parabasalian genus belonging to the order Trichomonadida. It presents four flagella, three forward-facing and one trailing, without the presence of a costa or any kind of undulating membrane. Monocercomonas is found in animal guts. and is susceptible to cause Monocercomoniasis in reptiles

<i>Phycophthorum</i> Genus of parasitic protists

Phycophthorum is a monotypic genus of protists that parasitize diatoms, containing the sole species Phycophthorum isakeiti. It was discovered in 2020 in the coastal waters of Norway, as parasites of diatoms belonging to the genus Pleurosigma.

References

  1. 1 2 Muehlstein, Lisa K.; Porter, David; Short, Frederick T. (1991-01-01). "Labyrinthula zosterae sp. nov., the Causative Agent of Wasting Disease of Eelgrass, Zostera marina". Mycologia. 83 (2): 180–191. doi:10.2307/3759933. JSTOR   3759933.
  2. 1 2 3 Cienkowski, L. (1867-12-01). "Ueber den Bau und die Entwickelung der Labyrinthuleen". Archiv für Mikroskopische Anatomie (in German). 3 (1): 274–310. doi:10.1007/BF02960460. ISSN   0176-7364. S2CID   83753548.
  3. 1 2 Pokorny, Kathryn Stein (1967-11-01). "Labyrinthula". The Journal of Protozoology. 14 (4): 697–708. doi:10.1111/j.1550-7408.1967.tb02065.x. ISSN   1550-7408.
  4. ↑ Patterson, D. J. (1989). "Stramenopiles, chromophytes from a protistan perspectives". The Chromaphyte Algae Problems and Perspectives: 357–379.
  5. 1 2 Zopf, W. (1892). "Zur Kenntnis der Labyrinthuleen einer Familie der Myceozoen". Beitr. Hysiol. Morphol. Nied. Organ. 2: 36–48.
  6. ↑ Tyler., Bonner, John (2015-12-08). Cellular Slime Molds. Princeton University Press. ISBN   9781400876884. OCLC   957504952.{{cite book}}: CS1 maint: multiple names: authors list (link)
  7. ↑ Honigberg, B. M.; Balamuth, W.; Bovee, E. C.; Corliss, J. O.; Gojdics, M.; Hall, R. P.; Kudo, R. R.; Levine, N. D.; Lobblich, A. R. (1964-02-01). "A Revised Classification of the Phylum Protozoa*". The Journal of Protozoology. 11 (1): 7–20. doi:10.1111/j.1550-7408.1964.tb01715.x. ISSN   1550-7408. PMID   14119564.
  8. 1 2 3 Bigelow, D. M.; Olsen, M. W.; Gilbertson, R. L. (2005-03-01). "Labyrinthula terrestris sp. nov., a new pathogen of turf grass". Mycologia. 97 (1): 185–190. doi:10.1080/15572536.2006.11832852. ISSN   0027-5514. PMID   16389970. S2CID   28774010.
  9. 1 2 3 Dyková, Iva; Fiala, Ivan; Dvořáková, Helena; Pecková, Hana (2008-11-01). "Living together: The marine amoeba Thecamoeba hilla Schaeffer, 1926 and its endosymbiont Labyrinthula sp". European Journal of Protistology. 44 (4): 308–316. doi:10.1016/j.ejop.2008.04.001. PMID   18619822.
  10. 1 2 Porter, David (1972-12-01). "Cell division in the marine slime mold, Labyrinthula sp., and the role of the bothrosome in extracellular membrane production". Protoplasma. 74 (4): 427–448. doi:10.1007/BF01281960. ISSN   0033-183X. S2CID   41333647.
  11. ↑ Sullivan, Brooke K.; Robinson, Katie L.; Trevathan-Tackett, Stacey M.; Lilje, Erna S.; Gleason, Frank H.; Lilje, Osu (2017-02-01). "The First Isolation and Characterisation of the Protist Labyrinthula sp. in Southeastern Australia". Journal of Eukaryotic Microbiology. 64 (4): 504–513. doi:10.1111/jeu.12387. hdl: 11343/292461 . ISSN   1550-7408. PMID   28004878. S2CID   162410.
  12. 1 2 Thomas., Moss, Stephen (1986-01-01). The biology of marine fungi. Cambridge University Press. ISBN   9780521308991. OCLC   610636209.{{cite book}}: CS1 maint: multiple names: authors list (link)
  13. 1 2 Raghukumar, Seshagiri (2002). "Ecology of the marine protists, the Labyrinthulomycetes (Thraustochytrids and Labyrinthulids)". European Journal of Protistology. 38 (2): 127–145. doi:10.1078/0932-4739-00832.
  14. 1 2 W., Dick, Michael (2010-01-01). Straminipilous Fungi. Springer Netherlands. ISBN   9789401597333. OCLC   961064561.{{cite book}}: CS1 maint: multiple names: authors list (link)
  15. 1 2 Perkins, Frank O.; Amon, James P. (1969-05-01). "Zoosporulation in Labyrinthula sp.; an Electron Microscope Study1". The Journal of Protozoology. 16 (2): 235–257. doi:10.1111/j.1550-7408.1969.tb02265.x. ISSN   1550-7408.
  16. ↑ Babtsch, G.; Bartsch, G. (1971-01-01). "Cytologische Beobachtungen an Labyrinthula coenocystis SCHMOLLER bei verschiedenen Kulturbedingungen". Zeitschrift für Allgemeine Mikrobiologie. 11 (2): 79–90. doi:10.1002/jobm.19710110202. ISSN   1521-4028.
  17. ↑ Brakel, Janina; Werner, Franziska Julie; Tams, Verena; Reusch, Thorsten B. H.; Bockelmann, Anna-Christina (2014-04-01). "Current European Labyrinthula zosterae Are Not Virulent and Modulate Seagrass (Zostera marina) Defense Gene Expression". PLOS ONE. 9 (4): e92448. Bibcode:2014PLoSO...992448B. doi: 10.1371/journal.pone.0092448 . ISSN   1932-6203. PMC   3972160 . PMID   24691450.
  18. 1 2 Muehlstein, LK (1989). "Perspectives on the wasting disease of eelgrass Zostera marina". Diseases of Aquatic Organisms. 7: 211–221. doi: 10.3354/dao007211 .
  19. ↑ Raghukumar, C (1987). "Fungal parasites of marine algae from Mandapam (South India)". Diseases of Aquatic Organisms. 3: 137–145. doi: 10.3354/dao003137 .
  20. ↑ Dangeard, P.A. (1932). "Observations sur la famille des Labyrin- thulees et sur quelques parasites des Cladophora". Le Botaniste. 24: 217.
  21. ↑ Karling, John S. (1944-01-01). "Phagomyxa algarum N. Gen., N. Sp., An Unusual Parasite with Plasmodiophoralean and Proteomyxean Characteristics". American Journal of Botany. 31 (1): 38–52. doi:10.2307/2437666. JSTOR   2437666.
  22. ↑ Hollande, A.; Enjumet, M. (1955). "Sur l'évolution et la systématique des Labyrinthulidae; étude de Labyrinthula algeriensis nov. sp". Annls. Sci. Nat. Zool. Biol. Anim. 17: 357–368.
  23. ↑ Chadefaud, M. (1956). "Sur un Labyrinthula de Roscoff". C. R. Acad. Sci. 243: 1794–1797.
  24. ↑ Schmoller, H. (1960). "Kultur und Entwicklung yon Labyrinthula coenocystis n. sp". Arch. Mikrobiol. 36 (4): 365–372. doi:10.1007/bf00418643. S2CID   6841006.
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.