Name: amoebozoa: movement and life cycles
Uploaded: 2025-06-05T06:27:20.000Z
Duration: 1 min 27 s
Channel: JoVE

I protisti degli Amoebozoi sono caratterizzati dai loro pseudopodi a forma di lobo. Include gymnamoebas, entamoebas e muffe melmose plasmodiali e cellulari.I gymnamoeba, come le specie di ameba, sono protisti a vita libera che abitano ambienti acquatici e del suolo.Al contrario, gli entamoeba sono parassiti e abitano principalmente la cavità orale o il tratto intestinale di vertebrati e invertebrati. L'agente patogeno umano Entamoeba histolytica è un esempio notevole.Le muffe melmose sono protisti mobili simili a funghi che producono corpi fruttiferi contenenti spore per la dispersione.Le muffe melmose plasmodiali come il Physarum esistono tipicamente come una singola massa nota come plasmodio nella loro fase vegetativa, che contiene più nuclei diploidi.Un plasmodio è mobile e produce sporangi contenenti spore aploidi. In condizioni favorevoli, queste spore si sviluppano in cellule flagellate che si fondono per rigenerare un plasmodio diploide.Al contrario, le muffe melmose cellulari come il Dictyostelium esistono come singole cellule aploidi nel loro stato vegetativo. Se affamati, si aggregano, formano masse mobili e si trasformano in corpi fruttiferi.

diversità_dei_protisti-iv

Diversity of Protists IV

Gli Amoebozoa rappresentano un gruppo eterogeneo di protisti terrestri e acquatici che utilizzano pseudopodi lobati per la locomozione e l&#8217;alimentazione. Questa caratteristica li differenzia dai Rhizaria, che possiedono pseudopodi filiformi. Le principali classificazioni all&#8217;interno degli Amoebozoa includono i ginnamoebe, gli entamoebe e le muffe mucillaginose plasmodiali e cellulari. Le evidenze filogenetiche indicano che gli Amoebozoa si siano evoluti da un lignaggio che ha successivamente dato origine a funghi e animali.
Ginnamoebe ed Entamoebe
I ginnamoebe sono protisti liberi che abitano ambienti acquatici e suoli. Il loro movimento &#232; facilitato dagli pseudopodi mediante un processo denominato movimento ameboide, che implica lo scorrimento citoplasmatico. In questo meccanismo, il citoplasma avanza in una regione meno contratta e pi&#249; fluida all&#8217;estremit&#224; anteriore della cellula, seguendo il percorso di minore resistenza. Questo flusso &#232; supportato da microfilamenti situati appena sotto la membrana citoplasmatica. I ginnamoebe presentano un&#8217;ampia variabilit&#224; dimensionale, da appena 15 micrometri di diametro fino a oltre 750 micrometri, dimensione visibile a occhio nudo.
Al contrario dei ginnamoebe liberi, gli entamoebe sono protisti parassiti che risiedono prevalentemente nella cavit&#224; orale o nel tratto intestinale di vertebrati e invertebrati. In particolare, Entamoeba histolytica &#232; una specie anaerobia che agisce come patogeno umano, causando la dissenteria amebica. Questa condizione comporta ulcerazioni del tratto intestinale e provoca diarrea ematica. La trasmissione di questo parassita avviene tramite cisti, che si diffondono per contaminazione fecale di acqua, alimenti e utensili da cucina.
Muffe Mucillaginose
Le muffe mucillaginose furono storicamente classificate insieme ai funghi a causa della somiglianza nei cicli vitali e nella produzione di corpi fruttiferi contenenti spore destinate alla dispersione. Tuttavia, a differenza dei funghi, esse mostrano motilit&#224;, che consente loro di spostarsi rapidamente su superfici solide. Questi organismi sono classificati in due grandi gruppi: muffe mucillaginose plasmodiali, note anche come acellulari, e muffe mucillaginose cellulari.
Le muffe mucillaginose plasmodiali esistono, nella fase vegetativa, come una massa amorfa di protoplasma nota come plasmodio (da non confondere con il genere patogeno Plasmodium responsabile della malaria), che contiene numerosi nuclei diploidi. Questo plasmodio &#232; attivamente mobile e si propaga tramite movimento ameboide. In condizioni favorevoli, forma degli sporangi, strutture contenenti spore aploidi. Queste spore germinano e si sviluppano in cellule flagellate mobili, che successivamente si fondono per rigenerare un plasmodio diploide. Un genere noto e ampiamente studiato &#232; Physarum.
Le muffe mucillaginose cellulari, invece, mantengono cellule aploidi individuali nella fase vegetativa e formano strutture diploidi solo in specifiche condizioni ambientali. La specie ampiamente studiata Dictyostelium discoideum presenta un ciclo vitale asessuato caratterizzato da aggregazione, migrazione e formazione del corpo fruttifero. In risposta alla carenza di nutrienti, le cellule individuali di Dictyostelium si aggregano per formare un pseudoplasmodio, nel quale le cellule perdono la propria individualit&#224; senza fondersi. Il processo di aggregazione &#232; indotto dal rilascio di adenosina monofosfato ciclico (cAMP), una molecola segnale che attira le cellule vicine. La massa aggregata, nota come &#8220;slug&#8221;, presenta motilit&#224; prima di arrestarsi e orientarsi verticalmente, fase in cui si avvia la formazione del corpo fruttifero.
Il corpo fruttifero &#232; composto da uno stelo e una testa. Le cellule dello stelo sintetizzano cellulosa, fornendo supporto strutturale, mentre le cellule della testa si differenziano in spore. Dopo la dispersione, queste spore germinano e danno origine a nuove cellule ameboidi, perpetuando cos&#236; il ciclo vitale. Oltre alla riproduzione asessuata, Dictyostelium pu&#242; anche compiere una riproduzione sessuata, durante la quale due amebe si fondono per formare una singola ameba gigante. Questa struttura sviluppa una parete spessa di cellulosa, formando un macrocisto che pu&#242; rimanere dormiente per lunghi periodi. Alla fine, all&#8217;interno del macrocisto avviene la meiosi, producendo nuclei aploidi che si integrano in nuove amebe, riavviando cos&#236; il ciclo asessuato.

Diversità_dei_Protisti-IV

Gli Amoebozoa rappresentano un gruppo eterogeneo di protisti terrestri e acquatici che utilizzano pseudopodi lobati per la locomozione e ...

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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, which depends on pseudopodia and cytoplasmic streaming. In this process, the cytoplasm flows into a less contracted, more fluid region at the front of the cell. Microfilaments just under the cell membrane support this movement. Gymnamoebas also vary widely in size, from about 15 micrometers across to more than 750 micrometers, which can be seen with the naked eye.

Entamoebas are parasitic protists that usually live in the mouth or intestinal tract of vertebrates and invertebrates. Entamoeba histolytica is an anaerobic species and a human pathogen. It causes amebic dysentery, which can ulcerate the intestinal tract and lead to bloody diarrhea. The parasite spreads through cysts that contaminate water, food, and eating utensils.

Slime molds were once grouped with fungi because both can form fruiting bodies that contain spores. Unlike fungi, however, slime molds can move quickly across solid surfaces. They are divided into plasmodial slime molds, also called acellular slime molds, and cellular slime molds. These two groups have different life cycles, but both use spore formation for dispersal.

Plasmodial slime molds live as a plasmodium in the vegetative stage. A plasmodium is an amorphous mass of protoplasm with many diploid nuclei, and it moves by amoeboid movement. When conditions are favorable, it forms sporangia that contain haploid spores. These spores germinate into flagellated swarm cells, which then fuse to form a new diploid plasmodium. Physarum is a well-known genus in this group.

Cellular slime molds stay as individual haploid cells during the vegetative stage. Under certain environmental conditions, they form diploid structures. Dictyostelium discoideum is the best-studied species in this group. Its asexual life cycle includes aggregation, migration, and fruiting body formation, and it can also undergo sexual reproduction. During starvation, cells release cAMP, or cyclic adenosine monophosphate, which attracts nearby cells and triggers aggregation into a pseudoplasmodium. The cells do not fuse, but they lose their individuality and form a moving slug.

The slug later becomes stationary and stands upright before fruiting body formation begins. The fruiting body has a stalk and a head. Stalk cells make cellulose for support, while head cells become spores. After dispersal, the spores germinate into new amoeboid cells. Dictyostelium can also reproduce sexually when two amoebae fuse to form a giant amoeba. This structure develops a thick cellulose wall and becomes a macrocyst that can stay dormant for a long time. Meiosis then occurs inside the macrocyst, producing haploid nuclei that give rise to new amoebae and restart the asexual cycle.

Amoebozoa: Movement and Life Cycles

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diversity of protists iv

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 Amoebozoa move with pseudopodia and how gymnamoebas, entamoebas, and slime molds grow, spread, and reproduce in different life cycles.

Amoebozoa: Movement and Life Cycles | 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.

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Amoebozoa: Movement and Life Cycles

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