Name: alveolates: ciliates, dinoflagellates, apicomplexans
Uploaded: 2025-06-12T09:27:31.000Z
Duration: 1 min 27 s
Channel: JoVE

Les alvéoles comprennent les ciliés, les dinoflagellés et les apicomplexes. Ils sont caractérisés par des alvéoles - des sacs cytoplasmiques situés sous la membrane cellulaire. Les ciliés tels que la paramécie sont reconnus par la présence de cils qui aident au mouvement. Les ciliés possèdent deux types de noyaux - les macronoyaux et les micronoyaux - qui sont impliqués dans la régulation des fonctions cellulaires de base et de la reproduction sexuée, respectivement. Les dinoflagellés sont des protistes photosynthétiques. Ils se déplacent avec un mouvement de rotation à l’aide de deux flagelles de longueurs différentes positionnés à des angles différents. Les espèces de Gonyaulax produisent une bioluminescence, émettant de la lumière lorsqu’elles sont dérangées, créant un effet scintillant dans les eaux côtières. Les apicomplexes sont des protistes non mobiles, non photosynthétiques et parasites. Ces organismes produisent généralement des sporozoïtes – des structures spécialisées qui aident à l’infection de l’hôte. Les apicomplexes contiennent également des apicoplastes, qui sont des chloroplastes dégénérés qui contribuent à la biosynthèse des acides gras, des isoprénoïdes et de l’hème. Les apicomplexes bien connus sont Plasmodium, qui cause le paludisme, et Toxoplasma, qui cause la toxoplasmose.

diversité des protozoaires

Diversity of Protists II

Les alv&#233;ol&#233;s forment un groupe d'organismes caract&#233;ris&#233;s par la pr&#233;sence d&#8217;alv&#233;oles, qui sont des sacs cytoplasmiques situ&#233;s sous la membrane cellulaire. Bien que leur fonction reste incertaine, les alv&#233;oles pourraient aider &#224; r&#233;guler l&#8217;&#233;quilibre hydrique en contr&#244;lant la quantit&#233; d&#8217;eau entrant et sortant de la cellule. Chez les dinoflagell&#233;s, ces structures peuvent servir de plaques de protection. Il existe trois principaux types d&#8217;alv&#233;ol&#233;s : les cili&#233;s, qui se d&#233;placent &#224; l&#8217;aide de cils ; les dinoflagell&#233;s, qui utilisent des flagelles pour se mouvoir ; et les apicomplex&#233;s, qui sont parasitaires et infectent les humains ainsi que d'autres animaux.
Les cili&#233;s poss&#232;dent des cils &#224; un moment donn&#233; de leur cycle de vie. Ces structures petites et ressemblant &#224; des poils facilitent la locomotion et peuvent recouvrir l&#8217;ensemble de la cellule ou appara&#238;tre en touffes ou en rang&#233;es, selon les esp&#232;ces. L&#8217;un des cili&#233;s les plus connus est le Paramecium, qui utilise ses cils &#224; la fois pour se d&#233;placer et pour se nourrir. Le Paramecium consomme des bact&#233;ries et d&#8217;autres particules en les entra&#238;nant vers un sillon oral en forme d&#8217;entonnoir. Le mat&#233;riel est ensuite dirig&#233; vers la bouche cellulaire, ou cytostome, o&#249; il est envelopp&#233; dans une vacuole par phagocytose. Des enzymes digestives d&#233;gradent alors le contenu afin d&#8217;en extraire les nutriments.
Les cili&#233;s sont uniques parmi les protistes en raison de la pr&#233;sence de deux types de noyaux : les micronoyaux et les macronoyaux. Le macronoyau r&#233;gule les fonctions cellulaires essentielles telles que la croissance et l&#8217;alimentation, tandis que le micronoyau intervient dans la reproduction sexu&#233;e. Chez le Paramecium, la reproduction sexu&#233;e a lieu lorsque deux cellules fusionnent partiellement pour &#233;changer leurs micronoyaux. Le g&#233;nome macronucl&#233;aire de Paramecium contient environ 40 000 g&#232;nes, soit pr&#232;s du double de celui des humains.
De nombreuses esp&#232;ces de Paramecium et d&#8217;autres protistes h&#233;bergent des bact&#233;ries, des arch&#233;es ou des eucaryotes endosymbiotiques, comme les algues vertes. Ces organismes symbiotiques fournissent souvent &#224; leur h&#244;te des nutriments essentiels, notamment des vitamines ou des facteurs de croissance. Certains cili&#233;s, en particulier ceux vivant dans les syst&#232;mes digestifs des termites, contiennent des arch&#233;es endosymbiotiques capables de convertir l&#8217;hydrog&#232;ne et le dioxyde de carbone en m&#233;thane. De plus, certains cili&#233;s ana&#233;robies sont pr&#233;sents dans le rumen des ruminants, o&#249; ils participent &#224; la digestion et &#224; la fermentation.
Bien que la symbiose soit fr&#233;quente, certains cili&#233;s sont parasitaires. Un exemple est Balantidium coli, un parasite intestinal principalement retrouv&#233; chez les animaux domestiques mais pouvant &#233;galement infecter les humains, provoquant des sympt&#244;mes proches de la dysenterie. Ce parasite forme des kystes qui permettent la transmission de la maladie via des aliments ou de l&#8217;eau contamin&#233;s.
Les dinoflagell&#233;s sont des organismes vari&#233;s pr&#233;sents dans les environnements marins et d&#8217;eau douce. Ils ont acquis leur capacit&#233; &#224; photosynth&#233;tiser gr&#226;ce &#224; une endosymbiose secondaire. Ces organismes se d&#233;placent &#224; l&#8217;aide de deux flagelles de longueurs diff&#233;rentes, plac&#233;s selon des angles distincts. Le mouvement de ces flagelles induit une rotation des dinoflagell&#233;s, ph&#233;nom&#232;ne refl&#233;t&#233; dans leur nom, d&#233;riv&#233; du grec signifiant &#171; tournoyer &#187;. Certains dinoflagell&#233;s sont libres, tandis que d&#8217;autres vivent en symbiose avec les animaux des r&#233;cifs coralliens, leur fournissant de la nourriture en &#233;change d&#8217;un abri.
Certains dinoflagell&#233;s produisent de la bioluminescence, &#233;mettant de la lumi&#232;re lorsqu&#8217;ils sont perturb&#233;s la nuit, cr&#233;ant un effet scintillant dans les eaux c&#244;ti&#232;res. Toutefois, certaines esp&#232;ces sont nuisibles. Par exemple, Gonyaulax forme des prolif&#233;rations denses appel&#233;es &#171; mar&#233;es rouges &#187;, pouvant provoquer la mort des poissons et des intoxications humaines lorsque les coquillages accumulent les neurotoxines produites par l&#8217;organisme. Cette condition, connue sous le nom d&#8217;intoxication paralysante par les coquillages, peut entra&#238;ner des engourdissements, des vertiges et des difficult&#233;s respiratoires, les cas graves pouvant aboutir &#224; une insuffisance respiratoire. Un autre dinoflagell&#233; toxique, Pfiesteria piscicida, lib&#232;re des spores toxiques qui infectent et tuent les poissons. Ces toxines provoquent &#233;galement des l&#233;sions, permettant aux bact&#233;ries d&#8217;envahir les tissus endommag&#233;s du poisson. Les humains expos&#233;s &#224; Pfiesteria peuvent d&#233;velopper des &#233;ruptions cutan&#233;es et des probl&#232;mes respiratoires.
Les apicomplex&#233;s sont des parasites non photosynth&#233;tiques responsables de maladies graves chez les humains et les animaux. Des exemples incluent Plasmodium, responsable du paludisme ; Toxoplasma, &#224; l&#8217;origine de la toxoplasmose ; et Eimeria, qui provoque la coccidiose. Les apicomplex&#233;s adultes sont immobiles et absorbent les nutriments directement &#224; travers leur membrane cellulaire.
Ces organismes produisent des sporozo&#239;tes, structures sp&#233;cialis&#233;es facilitant l&#8217;infection de l&#8217;h&#244;te. Le nom &#171; apicomplex&#233;s &#187; provient de la pr&#233;sence d&#8217;un complexe d&#8217;organites unique situ&#233; &#224; une extr&#233;mit&#233; du sporozo&#239;te, permettant au parasite d&#8217;envahir les cellules h&#244;tes. Les apicomplex&#233;s poss&#232;dent &#233;galement des apicoplastes, qui sont des chloroplastes d&#233;g&#233;n&#233;r&#233;s ne r&#233;alisant plus la photosynth&#232;se, mais contribuant encore &#224; la biosynth&#232;se des acides gras, des isopr&#233;no&#239;des et de l&#8217;h&#232;me. On pense que les apicoplastes proviennent d&#8217;algues rouges ayant &#233;t&#233; phagocyt&#233;es par un anc&#234;tre des apicomplex&#233;s lors d&#8217;un &#233;v&#233;nement d&#8217;endosymbiose secondaire. Au fil du temps, le chloroplaste a perdu sa capacit&#233; de photosynth&#232;se et a adopt&#233; d&#8217;autres fonctions au sein de la cellule apicomplex&#233;e.
Les apicomplex&#233;s infectent aussi bien les vert&#233;br&#233;s que les invert&#233;br&#233;s, et certaines esp&#232;ces n&#233;cessitent deux h&#244;tes pour compl&#233;ter leur cycle de vie. Par exemple, certaines esp&#232;ces de Plasmodium, responsables du paludisme, alternent entre un h&#244;te moustique et un h&#244;te humain. Les coccidies infectent principalement les oiseaux mais peuvent &#233;galement toucher d'autres animaux. Le paludisme, l&#8217;une des maladies les plus mortelles de l&#8217;histoire humaine, demeure une menace sanitaire majeure &#224; l&#8217;&#233;chelle mondiale.

Diversité des protozoaires

Les alv&#233;ol&#233;s forment un groupe d'organismes caract&#233;ris&#233;s par la pr&#233;sence d&#8217;alv&#233;oles, qui sont des sacs cytoplasmiques ...

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alveolates: ciliates, dinoflagellates, apicomplexans

Alveolates are protists with tiny sacs called alveoli beneath the cell membrane. These sacs may help control water balance by limiting how much water moves in and out of the cell. In dinoflagellates, alveoli may also act like armor plates.

The three main alveolate groups are ciliates, dinoflagellates, and apicomplexans. Ciliates move with cilia, which are short hair-like structures that can cover the whole cell or appear in rows or tufts. One well-known ciliate is Paramecium, which uses cilia for movement and for feeding on bacteria and other small particles.

Paramecium sweeps food into a funnel-shaped oral groove. The food then moves to the gullet, or cell mouth, where it is enclosed in a vacuole by phagocytosis. Digestive enzymes break the food down so the cell can absorb nutrients. Ciliates are also unusual because they have two nuclei. The macronucleus controls everyday cell functions such as growth and feeding, while the micronucleus is involved in sexual reproduction.

In Paramecium, sexual reproduction happens when two cells partially join and exchange micronuclei. The macronuclear genome of Paramecium has about 40,000 genes, which is nearly twice as many as humans. Many Paramecium species and other protists also host endosymbiotic bacteria, archaea, or eukaryotes such as green algae. These partners often supply vitamins or growth factors to the host.

Some ciliates have more specialized symbioses. Ciliates in termite digestive tracts can contain archaea that turn hydrogen and carbon dioxide into methane. Other anaerobic ciliates live in the rumen of ruminant animals and help with digestion and fermentation. Not all ciliates are helpful, though. Balantidium coli is an intestinal parasite that mainly infects domestic animals but can sometimes infect humans and cause dysentery-like symptoms. It spreads through cysts in contaminated food or water.

Dinoflagellates live in both marine and freshwater habitats. They gained photosynthesis through secondary endosymbiosis. They move with two flagella of different lengths that are set at different angles. This movement makes the cell spin, which fits the name dinoflagellate, from a Greek word meaning “whirling.”

Some dinoflagellates live freely, while others live with coral reef animals and provide food in exchange for shelter. Certain species also produce bioluminescence, so they glow when disturbed at night. Other dinoflagellates can be harmful. Gonyaulax can form red tides, which may kill fish and poison humans when shellfish collect its neurotoxins. This can cause paralytic shellfish poisoning, with numbness, dizziness, breathing trouble, and in severe cases respiratory failure. Pfiesteria piscicida is another harmful dinoflagellate. It releases toxic spores that infect and kill fish, and the toxins can also cause lesions that let bacteria enter damaged tissue. Humans exposed to Pfiesteria may develop skin rashes and breathing problems.

Apicomplexans are non-photosynthetic parasites that cause serious disease in humans and animals. Examples include Plasmodium, which causes malaria; Toxoplasma, which causes toxoplasmosis; and Eimeria, which causes coccidiosis. Adult apicomplexans do not move and absorb nutrients through their cell membrane. They form sporozoites, which help start infection in a host. Their name comes from a special organelle complex at one end of the sporozoite that helps the parasite enter host cells.

Apicomplexans also contain apicoplasts. These are degenerate chloroplasts that no longer do photosynthesis, but they still help with fatty acid, isoprenoid, and heme synthesis. Scientists think apicoplasts came from red algae in a secondary endosymbiotic event. Apicomplexans infect both vertebrates and invertebrates, and some need two hosts to finish their life cycle. In some Plasmodium species, the parasite alternates between mosquito and human hosts. Coccidia mainly infect birds, but they can also affect other animals. Malaria has been one of the deadliest diseases in human history and remains a major health threat worldwide.

Alveolates: Ciliates, Dinoflagellates, Apicomplexans

alveolates-ciliates-dinoflagellates-apicomplexans

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overview of protists

Protist Diversity, Movement, and Survival

Protists are diverse eukaryotic microorganisms with many ways to move, eat, and survive. They do not have the specialized tissues of plants and animals or the chitinous cell walls of fungi. Their early split within Eukarya led to major structural, functional, and ecological diversity. Scientists group protists into supergroups based on genetic analysis and shared structures. These groups include Archaeplastida, Excavata, Amoebozoa, Rhizaria, Alveolata, and Stramenopiles. This classification...

diversity of protists i

Excavata Protists and Their Adaptations

Excavata protists show many different ways of living, from photosynthesis to parasitism. This group includes organisms that can use chemical energy, light, or both. Some also live in low-oxygen, or anaerobic, environments where they survive without normal oxygen-based metabolism. Among the main Excavata groups are diplomonads and parabasalids. These are flagellated protists, meaning they move with whip-like tails, and they lack mitochondria and chloroplasts. They often live in anoxic habitats,...

diversity of protists ii

Alveolates are protists with tiny sacs called alveoli beneath the cell membrane. These sacs may help control water balance by limiting how much water moves in and out of the cell. In dinoflagellates, alveoli may also act like armor plates. The three main alveolate groups are ciliates, dinoflagellates, and apicomplexans. Ciliates move with cilia, which are short hair-like structures that can cover the whole cell or appear in rows or tufts. One well-known ciliate is Paramecium, which uses cilia...

diversity of protists iii

Rhizaria: Pseudopods, Tests, and Skeletons

Rhizaria are unicellular protists with threadlike pseudopodia, which are thin cytoplasmic extensions used for movement and feeding. Their amoeboid shape once caused taxonomic confusion, but molecular phylogenetics has since shown where they fit on the evolutionary tree. This group includes Chlorarachniophyta, Radiolaria, and Foraminifera, and each lineage has adapted to a different ecological niche and metabolic strategy. Chlorarachniophyta are unicellular phototrophic protists found in marine...

diversity of protists iv

Amoebozoa: Movement and Life Cycles

Amoebozoa are a diverse group of terrestrial and aquatic protists. They move and feed with lobe-shaped pseudopodia. This feature sets them apart from Rhizaria, which have threadlike pseudopodia. The group includes gymnamoebas, entamoebas, and the plasmodial and cellular slime molds. Phylogenetic evidence also shows that Amoebozoa split from a lineage that later gave rise to fungi and animals. Gymnamoebas are free-living protists that live in water and soil. They move by amoeboid movement,...

key terms and concepts

Learn how alveolates include ciliates, dinoflagellates, and apicomplexans, from Paramecium feeding to red tides, parasites, and malaria.

Alveolates: Ciliates, Dinoflagellates, Apicomplexans | JoVE K12

JoVE Core Microbiology provides an engaging introduction to the microbial world and its influence on health, industry, and the environment. This comprehensive collection covers key concepts such as microbial structure, metabolism, genetics, and ecology. It introduces essential laboratory techniques and microscopy methods through visually engaging animations. Corresponding scientist-in-action videos bridge classroom concepts with real-world research and applications.

microbiology

Alveolates: Ciliates, Dinoflagellates, Apicomplexans

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