Thevampyrellids (orderVampyrellida, classVampyrellidea), colloquially known asvampire amoebae, are a group of free-livingpredatoryamoebae classified as part of the lineageEndomyxa. They are distinguished from other groups of amoebae by their irregular cell shape with propensity to fuse and split likeplasmodial organisms, and theirlife cycle with a digestivecyst stage thatdigests the gathered food. They appearworldwide inmarine,brackish,freshwater andsoil habitats. They are important predators of an enormous variety of microscopic organisms, fromalgae tofungi andanimals.[3] They are also known asaconchulinid amoebae (orderAconchulinida).[4]
Vampyrellids are traditionally consideredfilose amoebae, i.e. they generate slender pseudopodia (filopodia). They are naked, devoid of external structures such as scales, cell coats or aglycocalyx, although there may be a temporarymucilage coat in thetrophozoite stage. The trophozoites vary greatly in shape, size and color between species, but can be grouped into three cell states or 'morphotypes': isodiametric, expanded, and 'filoflabellate'.[1][3]
Isodiametric (spherical) morphotype, common in algivorousVampyrella andLateromyxa, with radiating filopodia. Some species float in the water column, resemblingheliozoa in shape. Others crawl on the surface by concentrating stiff filopodia at the anterior region of the cell, attaching them to the surface, retracting and moving them towards the posterior region.[3]
Expanded morphotype, the most common, bound to the surface, with a variety of shapes (for example, either fan-shaped or branched inLeptophrys; with large, hyaline lamellae with thread-like filopodia inSericomyxa; highly branched or reticulate, inPlatyreta andThalassomyxa).[3]
Filoflabellate morphotype, only found inPlacopus, with flattened elliptical, spherical or fan-shaped cells that exhibit a clear separation between thegranuloplasmic cell hump and thehyaloplasmic lamellae, sometimes called 'lamellipodia'. There are numerous filopodia on the ventral side of the cell. Some of these trophozoites resembleamoebozoans such asvannellids, except for the presence of filopodia. They move by rolling over the filopodia that are anchored to the substrate.[3]
The three distinct morphotypes of vampyrellid amoebae
Motile cell after feeding (J), early (K) and mature (L) digestive cysts, cyst with daughter cells after internal plasmotomy (M)Large, bulkyplasmodium ofVampyrella lateritiaVampyrella lateritia resting cyst with four envelopes
The mobile, amoeboid cells, called 'trophozoites' or 'swarmers'[a] in old literature. Their main activity is to disperse, search and gather food throughphagocytosis.[3]
The immobile but highlymetabolically active 'digestivecyst' stage, that appears after the feeding. In some species it is called a 'resting phase', but it is different from a true resting cyst (orspore) that is metabollically inactive to survive adverse conditions. To reach this stage, the trophozoite retracts itsfilopodia,secretes a layeredcell wall, and strongly attaches itself to the substrate or floats freely. Either a central mainvacuole or multiple separate vacuoles appear to digest the food. The cytoplasm color may change to a bright red, orange or yellow color, or remain colorless. When the digestive phase is finished, one or multiple trophozoites hatch from the cyst through holes in the cell wall.[3]
In some species, near the end of the digestive cyst stage,asexual reproduction takes place inside the cyst through acell division (called 'internalplasmotomy'), resulting in 2–4daughter cells. These cells are released as young trophozoites through the holes. Other species do not divide inside the closed cyst, and instead divide during or after the hatching process ('external plasmotomy').Lateromyxa gallica shows an unusual mode of reproduction: while feeding on the inside ofalgal cells, theplasmodiashed and develop into digestive cysts.[3]
Many vampyrellid species have more than onenucleus and behave likeplasmodia. They can fuse their cells upon contact, and split apart when moving in opposite directions. Some species readily grow plasmodia as large as aPetri dish under laboratory conditions, while others only fuse when the cell density is high and the food availability is low. It is uncertain to what extend this can happen in the natural environment. In contrast,Placopus species are rarely ever seen with more than two nuclei.[3]
Under adverse environmental conditions, vampyrellids can transform into several types of resting stages:[3]
Hypnocysts, thin-walled and devoid of food content, formed when the trophozoite is disturbed by external stress.[3]
Secondary cysts, thin-walled and devoid of food content, formed as a result of starvation.[3]
True resting cysts, also called 'sporocysts' or 'spores' in old literature. They form in natural samples and old cultures, when there is no food or the conditions are unfavorable. They build several cyst walls and condense their cellular contents. They can survive events of desiccation or freezing, up to at least three years.[3]
Vampyrellids have evolved strategies to deal with relatively large bulky prey that are difficult to consume. They display at least four different feeding strategies to engulf entireprey or to devour the contents of othereukaryoticcells. These feeding strategies are not mutually exclusive, and the same species can display each with a different type of prey.[3]
Free capture. Similarly to amoebae of othersupergroups, they catch and enclose their prey within afood vacuole by usualphagocytosis. Some can paralyse their prey before the enclosement. The size of the enveloping is widely varied, from numerous small cells at the same time to entire nematodes or colonial green algae.[3]
Colony invasion. They attach to the colonies ofvolvocalean algae, dissolve and penetrate the extracellular gelatinousmucilage matrix, andphagocytose individual cells inside the colony. Possibly for protection against predators, they transform into digestive cysts inside of the colony.[3]
Protoplast extraction, the most famous strategy. They specifically remove, ingest and digest the cellular contents of their prey, always by dissolving the prey's organiccell wall or simply displacing the prey's siliceous wall, and invading through pseudopodia (called 'calyculopodia') to remove the cell contents . Some species eject the prey cytoplasm by applying pressure, a process known as 'plasmoptysis', which is followed by a rapid formation of a large vacuole. This process resembles a sucking motion, and is likely the reason for their comparison tovampires. In marine species no plasmoptysis is observed, which suggests that theosmotic pressure given bysalinity is important for plasmoptysis.[3]
Prey infiltration. Similarly to protoplast extractors, they perforate the cell wall of an algal prey, but invade the cell itself and completes the cycle within it. Some are able to move laterally from one cell to the next in filamentous prey. They divide into smaller portions that turn into digestive cysts.[3]
Vampyrellids have a long history of research. They are known for thevampire-like feeding habit of several vampyrellid amoebae, which pierce thecell walls of other eukaryotic cells to feed specifically on the cell contents, a feeding mechanism known as protoplast extraction. This similarity lead to the origin of the name for their most popular genus,Vampyrella, and their colloquial name 'vampire amoebae'.[3]
One of the earliest unambiguous reports of a vampyrellid is the mid-19th century description ofAmoeba lateritia (now known asVampyrella lateritia) by the German botanistGeorg Fresenius.[13] The first extensive documentation of theirlife history and feeding behavior was provided in 1865 by the Polish protozoologistLeon Cienkowski, who created the genusVampyrella and classified it in a subgroup of the 'monads',[14] apolyphyletic assemblage ofparasitoidprotists. Posterior works and monographs described numerous aquatic vampyrellid species, with important observations of their behaviour and ecology. In 1885, the German mycologistWilhelm Zopf demonstrated the presence ofnuclei in vampyrellids and erected the first family,Vampyrellidae.[15][16][3]
In the mid-20th century the first discoveries of soil-dwelling Vampyrellida were made. The first vampyrellid laboratoryculture was established, containing the soil amoebaTheratomyxa weberi that fed onnematodes. Similar soil amoebae were isolated later, and studied as possible pest control against plant-pathogenic nematodes.[17] Other studies identified a giant soil vampyrellid as the organism responsible for perforations found infungalspores.[18][3]
Vampyrellida represents one of the major groups of free-livingamoebae, phylogenetically separate from other groups of amoebae such asAmoebozoa,Heterolobosea andNucleariidae. Instead, Vampyrellida is an isolatedclade within theRhizariasupergroup.[26] They are the closest relatives of thePhytomyxea,parasites ofplants andalgae that, unlike vampyrellids, disperse through flagellated stages during their life cycle and spend most of their active life within host cells.[3] Current classifications place both Vampyrellida and Phytomyxea, along with other small groups ofRhizaria, within the phylumEndomyxa.[4] Several phylogenetic analyses have recovered asister group relationship between Vampyrellida and Phytomyxea and have named their cladeProteomyxia[2] orPhytorhiza.[27]
There are currently 48 credible vampyrellidspecies distributed in 10 genera, scattered across five well-establishedclades found throughgenetic data, four of which arefamilies. Despite the advances, most of the vampyrellid diversity is still unknown or undescribed.[3]
FamilyVampyrellidaeZopf 1885 emend. Hess, Sausen et Melkonian 2012[1]
^The term 'swarmers' is more specially used forciliated, swimming cells such asgametes, sotrophozoites is a more appropriate term.[3]
^Not to be confused with the diatom genusHyalodiscusEhrenberg 1845, which takes preference in thebiological nomenclature for being described earlier.[3]
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^Song H, Zhang Y, Leng X, Zhang Y, Yu Y (2015). "Aconchulinid testate amoebae play an important role in nutrient cycling in freshwater ecosystems".Soil Biology and Biochemistry.82:1–7.doi:10.1016/j.soilbio.2014.11.009.
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^Zopf W (1885). "Die Pilzthiere oder Schleimpilze" [The Fungal Animals or Slime Molds]. In Schenk A (ed.).Handbuch der Botanik (Encyklopädie der Naturwissenschaften) [Handbook of Botany (Encyclopedia of Natural Sciences)] (in German). Vol. 3. Trewendt, Breslau. pp. 1–174.
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^Hülsmann N (1983). "On the penetration of algal cell walls during the attacks by vampyrellids".Journal of Protozoology.30: A50.
^Hülsmann N (1985). "Entwicklung und Ernährungsweise vonVampyrella lateritia (Rhizopoda)" [Development and feeding habits ofVampyrella lateritia (Rhizopoda)].Publ. Wiss. Film, Sekt. Biol., Ser. 17, Nr. 16/C.17:1–23.
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^Page FC (1987). "The classification of 'naked' amoebae (Phylum Rhizopoda)".Archiv für Protistenkunde.133 (3–4):199–217.doi:10.1016/S0003-9365(87)80053-2.
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