Name: excavata protists and their adaptations
Uploaded: 2025-06-12T09:27:15.000Z
Duration: 1 min 15 s
Channel: JoVE

Excavata to zróżnicowana grupa protistów, obejmująca zarówno gatunki chemoorganotroficzne, jak i fototroficzne. Do kluczowych grup należą diplomonady, parabasalidy i euglenozoany. Diplomonady takie jak Giardia charakteryzują się dwoma jądrami i mitosomami, które są słabo rozwiniętymi mitochondriami niezdolnymi do produkcji ATP. Parabasalidy to gatunki beztlenowe z ciałem przypodstawnym. Trichomonas jest wybitnym przykładem, pozbawionym mitochondriów, ale zawierającym hydrogenosomy, które wytwarzają ATP z gazowym wodorem jako produktem ubocznym. Euglenozoany są gatunkami ruchliwymi, posiadającymi zdolność do funkcjonowania zarówno jako chemotrofy, jak i fototrofy. Większość gatunków ma zazwyczaj dwie wici, ale tylko jedna jest widoczna na zewnątrz, wyłaniając się z przedniej kieszeni wiciowej. Reprezentatywny przykład, Euglena, wykazuje miksotrofię. Rozwija się w obecności światła, ale dłuższy okres ciemności może spowodować, że straci chloroplasty i przejdzie w chemoorganotroficzny tryb metabolizmu.

różnorodność pierwotniaków

Diversity of Protists I

Excavata to zr&#243;&#380;nicowana grupa protist&#243;w obejmuj&#261;ca zar&#243;wno organizmy chemoorganotroficzne, jak i fototroficzne, z kt&#243;rych niekt&#243;re rozwijaj&#261; si&#281; w &#347;rodowiskach beztlenowych. Do kluczowych grup w obr&#281;bie Excavata nale&#380;&#261; diplomonady i parabasalia, b&#281;d&#261;ce wiciowcami pozbawionymi mitochondri&#243;w i chloroplast&#243;w. Mikroorganizmy te zazwyczaj zasiedlaj&#261; &#347;rodowiska beztlenowe, takie jak jelita zwierz&#261;t, gdzie wyst&#281;puj&#261; w formie symbiont&#243;w lub paso&#380;yt&#243;w, korzystaj&#261;c z fermentacji jako g&#322;&#243;wnego mechanizmu pozyskiwania energii. Niekt&#243;re diplomonady s&#261; odpowiedzialne za powa&#380;ne choroby ryb, zwierz&#261;t domowych oraz ludzi, natomiast konkretne gatunki parabazali&#243;w wywo&#322;uj&#261; jedn&#261; z g&#322;&#243;wnych chor&#243;b przenoszonych drog&#261; p&#322;ciow&#261; u ludzi. Obie grupy maj&#261; stosunkowo niedawnego wsp&#243;lnego przodka, zanim uleg&#322;y rozdzieleniu na odr&#281;bne linie ewolucyjne.
Diplomonady charakteryzuj&#261; si&#281; obecno&#347;ci&#261; dw&#243;ch j&#261;der o jednakowej wielko&#347;ci oraz posiadaniem mitosom&#243;w, czyli silnie zredukowanych mitochondri&#243;w pozbawionych bia&#322;ek transportu elektron&#243;w i enzym&#243;w cyklu kwasu cytrynowego. Znacz&#261;cym przedstawicielem tej grupy jest Giardia, posiadaj&#261;ca stosunkowo niewielki i zwarty genom, niemal ca&#322;kowicie pozbawiony intron&#243;w oraz gen&#243;w koduj&#261;cych szlaki metaboliczne zwi&#261;zane z cyklem kwasu cytrynowego. Te cechy genetyczne s&#261; zgodne z jej paso&#380;ytniczym i beztlenowym stylem &#380;ycia. Gatunek Giardia intestinalis, znany tak&#380;e jako Giardia lamblia, wywo&#322;uje giardioz&#281; &#8211; powszechn&#261; chorob&#281; biegunkow&#261; przenoszon&#261; drog&#261; wodn&#261; w Stanach Zjednoczonych.
Parabasalia posiadaj&#261; charakterystyczn&#261; struktur&#281; zwan&#261; cia&#322;kiem parabazalnym, kt&#243;ra pe&#322;ni funkcj&#281; podporow&#261; dla aparatu Golgiego. Te beztlenowe protisty nie maj&#261; mitochondri&#243;w, lecz zawieraj&#261; hydrogenosomy, bior&#261;ce udzia&#322; w metabolizmie energetycznym. Parabasalia s&#261; powszechnie obecne w przewodzie pokarmowym i drogach moczowo-p&#322;ciowych kr&#281;gowc&#243;w i bezkr&#281;gowc&#243;w, gdzie funkcjonuj&#261; jako paso&#380;yty lub symbionty komensalne. Znanym przyk&#322;adem jest Trichomonas vaginalis &#8211; organizm wiciowy powoduj&#261;cy szeroko rozpowszechnion&#261; infekcj&#281; przenoszon&#261; drog&#261; p&#322;ciow&#261; u ludzi. Genomy parabasali&#243;w wyr&#243;&#380;niaj&#261; si&#281; unikaln&#261; struktur&#261; w&#347;r&#243;d eukariont&#243;w, jako &#380;e na og&#243;&#322; pozbawione s&#261; intron&#243;w. Genom T. vaginalis jest szczeg&#243;lnie du&#380;y jak na organizm paso&#380;ytniczy i zawiera oko&#322;o 160 milion&#243;w par zasad. Wykazuje r&#243;wnie&#380; oznaki horyzontalnego transferu gen&#243;w z bakterii oraz cechuje si&#281; du&#380;&#261; liczb&#261; powtarzaj&#261;cych si&#281; sekwencji i element&#243;w transpozycyjnych, co utrudnia analiz&#281; genomow&#261;. Pomimo tych z&#322;o&#380;ono&#347;ci, szacuje si&#281;, &#380;e T. vaginalis posiada blisko 60 000 gen&#243;w &#8211; niemal dwukrotnie wi&#281;cej ni&#380; genom ludzki, co czyni go jednym z najwi&#281;kszych znanych genom&#243;w eukariotycznych.
Kinetoplastydy stanowi&#261; kolejn&#261; wa&#380;n&#261; grup&#281; w obr&#281;bie Excavata, nazwan&#261; od kinetoplastu &#8211; zwartej masy DNA zlokalizowanej w ich pojedynczym, du&#380;ym mitochondrium. Organizmy te zamieszkuj&#261; g&#322;&#243;wnie &#347;rodowiska wodne, gdzie &#380;ywi&#261; si&#281; bakteriami, jednak niekt&#243;re gatunki s&#261; paso&#380;ytami powoduj&#261;cymi ci&#281;&#380;kie choroby u ludzi i zwierz&#261;t. Rodzaj Trypanosoma obejmuje patogeny zaka&#380;aj&#261;ce ludzi, takie jak Trypanosoma brucei, kt&#243;ry powoduje afryka&#324;sk&#261; &#347;pi&#261;czk&#281;. Choroba ta ma przewlek&#322;y, zazwyczaj &#347;miertelny przebieg i przenika z krwiobiegu do o&#347;rodkowego uk&#322;adu nerwowego, wywo&#322;uj&#261;c zapalenie m&#243;zgu i rdzenia kr&#281;gowego oraz objawy neurologiczne. Paso&#380;yt przenoszony jest przez much&#281; tse-tse (Glossina), owada krwiopijnego wyst&#281;puj&#261;cego w okre&#347;lonych regionach Afryki. Po dostaniu si&#281; do muchy paso&#380;yt namna&#380;a si&#281; w jej jelicie, a nast&#281;pnie migruje do gruczo&#322;&#243;w &#347;linowych, sk&#261;d mo&#380;e zosta&#263; przeniesiony do nowego gospodarza podczas uk&#261;szenia.
Inne paso&#380;ytnicze kinetoplastydy atakuj&#261;ce ludzi to Trypanosoma cruzi, wywo&#322;uj&#261;ca chorob&#281; Chagasa, oraz gatunki Leishmania, odpowiedzialne za leiszmanioz&#281;. Choroba Chagasa przenoszona jest przez uk&#261;szenie krwiopijnego owada zwanego "pluskw&#261; ca&#322;uj&#261;c&#261;". Cho&#263; cz&#281;sto ma ona charakter samoograniczaj&#261;cy si&#281;, mo&#380;e przekszta&#322;ci&#263; si&#281; w przewlek&#322;&#261; i potencjalnie &#347;mierteln&#261; posta&#263;. Leiszmanioza, wyst&#281;puj&#261;ca w rejonach tropikalnych i subtropikalnych, przenoszona jest przez much&#243;wk&#281; piaskow&#261; i mo&#380;e objawia&#263; si&#281; jako miejscowe infekcje sk&#243;rne lub jako uk&#322;adowa choroba atakuj&#261;ca &#347;ledzion&#281; i w&#261;trob&#281;, potencjalnie zagra&#380;aj&#261;ca &#380;yciu.
Euglenidy, kolejna dobrze poznana grupa w obr&#281;bie Excavata, charakteryzuj&#261; si&#281; niepatogennym charakterem oraz zdolno&#347;ci&#261; do funkcjonowania zar&#243;wno jako chemotrofy, jak i fototrofy. Te ruchliwe mikroorganizmy eukariotyczne, w wi&#281;kszo&#347;ci niepatogenne protisty, mog&#261; funkcjonowa&#263; jako fototrofy i heterotrofy. Wi&#281;kszo&#347;&#263; posiada dwa wici wychodz&#261;ce z przedniej kieszeni wiciowej, z kt&#243;rych widoczna z zewn&#261;trz jest tylko jedna, umo&#380;liwiaj&#261;ca poruszanie si&#281; mi&#281;dzy &#347;rodowiskami o r&#243;&#380;nym nat&#281;&#380;eniu &#347;wiat&#322;a, co wspiera ich elastyczne strategie &#380;ywieniowe. Euglenidy wyst&#281;puj&#261; powszechnie w &#347;rodowiskach wodnych, zar&#243;wno s&#322;odkowodnych, jak i morskich, a wiele gatunk&#243;w zawiera chloroplasty umo&#380;liwiaj&#261;ce wzrost fototroficzny. Jednak w warunkach braku &#347;wiat&#322;a kom&#243;rki Euglena, b&#281;d&#261;cej reprezentantem euglenid&#243;w, mog&#261; traci&#263; chloroplasty i przechodzi&#263; na chemoorganotroficzny spos&#243;b metabolizmu. Ponadto wiele euglenid&#243;w jest zdolnych do fagocytozy &#8211; procesu, w kt&#243;rym otaczaj&#261; kom&#243;rki bakteryjne elastyczn&#261; b&#322;on&#261; cytoplazmatyczn&#261;, umo&#380;liwiaj&#261;c ich wewn&#281;trzne trawienie.

Różnorodność pierwotniaków

Excavata to zr&#243;&#380;nicowana grupa protist&#243;w obejmuj&#261;ca zar&#243;wno organizmy chemoorganotroficzne, jak i fototroficzne, z kt&#243;rych ...

Education

JoVE Core

Microbiology

Mikrobiologia

Unit

Jednostka

Microbial Diversity

Różnorodność mikrobiologiczna

KEY TERMS AND CONCEPTS

KLUCZOWE TERMINY I POJĘCIA

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, such as the intestines of animals, where they may be symbionts or parasites and depend on fermentation for energy. Some members cause major diseases in fish, domestic animals, and humans. A parabasalid species also causes a major sexually transmitted disease in humans. The two groups likely shared a recent common ancestor before they split into separate lineages.

Diplomonads are known for having two nuclei of equal size. They also have mitosomes, which are highly reduced mitochondria. Mitosomes do not contain electron-transport proteins or the enzymes used in the citric acid cycle. Giardia is a well-known diplomonad with a small, compact genome, very few introns, and no genes for citric acid cycle pathways. These features fit its parasitic, anaerobic lifestyle. Giardia intestinalis, also called Giardia lamblia, causes giardiasis, a common waterborne diarrheal disease in the United States.

Parabasalids have a structure called the parabasal body, which supports the Golgi complex. They lack mitochondria but contain hydrogenosomes, which help with energy metabolism. These protists are often found in the intestinal and urogenital tracts of vertebrates and invertebrates. In these places, they may live as parasites or as commensal symbionts. Trichomonas vaginalis is a flagellated parabasalid that causes a widespread sexually transmitted infection in humans.

Parabasalid genomes are unusual among eukaryotes because they generally lack introns. The genome of T. vaginalis is especially large for a parasite, at about 160 megabase pairs. It also shows signs of horizontal gene transfer from bacteria and contains many repetitive regions and transposable elements, which makes genomic study difficult. Even with these complications, T. vaginalis is estimated to have nearly 60,000 genes. That is nearly twice the number in the human genome and one of the largest known eukaryotic genomes.

Kinetoplastids are another major Excavata group. They are named for the kinetoplast, a dense mass of DNA found in their single, large mitochondrion. Most live in aquatic habitats and feed on bacteria, but some are parasites that cause serious disease in humans and animals. Trypanosoma brucei causes African sleeping sickness, a chronic and usually fatal disease that moves from the bloodstream to the central nervous system. It is spread by the tsetse fly, Glossina, a blood-feeding insect from parts of Africa. The parasite multiplies in the fly’s intestine and moves to the salivary glands, where it can infect a new human host through a bite. Other human-infecting kinetoplastids include Trypanosoma cruzi, which causes Chagas disease, and Leishmania species, which cause leishmaniasis. Chagas disease spreads through the bite of the blood-feeding kissing bug and can become chronic and fatal. Leishmaniasis is found in tropical and subtropical regions and is spread by sand flies. It can cause skin infections or a more serious systemic disease that affects the spleen and liver.

Euglenids are another well-studied Excavata group and are usually nonpathogenic. They can act as both chemotrophs and phototrophs, so they can get energy from chemicals or from light. Most have two flagella from an anterior flagellar pocket, but only one is visible outside the cell. This helps them move between bright and dark environments and supports their flexible feeding strategies. Euglenids are common in freshwater and marine habitats, and many contain chloroplasts for phototrophic growth. In low light, Euglena can lose its chloroplasts and switch to a chemoorganotrophic way of life. Many euglenids can also carry out phagocytosis, where they engulf bacterial cells with their flexible membrane and digest them inside the cell.

Excavata Protists and Their Adaptations

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overview of algae

Algae Structure, Habitats, and Reproduction

Algae are simple eukaryotic photoautotrophs that live in many habitats and show a wide range of body forms. They contain chlorophyll and carry out oxygenic photosynthesis. They belong to the kingdom Archaeplastida, which also includes red and green algae and land plants. Unlike other protists with chloroplasts from secondary endosymbiosis, red and green algae came from primary endosymbiotic events. Algae can look very different from one another. Some are large brown kelp in coastal waters,...

red algae

Red Algae Pigments, Shapes, and Uses

Red algae are phototrophic organisms found mostly in marine environments. Some species also live in freshwater or on land. They may be unicellular or multicellular, and some multicellular forms grow large enough to be seen easily. These algae contain chlorophyll a, but their chloroplasts do not contain chlorophyll b. Instead, they use phycobiliproteins, which are light-harvesting pigments like those found in cyanobacteria. The red color seen in many species comes from phycoerythrin, an...

green algae

Green Algae: Forms, Habitats, and Roles

Green algae are photosynthetic organisms with chlorophylls a and b in their chloroplasts. These pigments give them a green color. They differ from red algae because they lack phycobiliproteins, the pigments that produce red or blue-green tones in red algae. In pigment makeup, green algae are close to plants, and they share a close evolutionary relationship with them. Green algae belong to Phylum Chlorophyta in the Kingdom Archaeplastida. They are usually divided into two main groups:...

other algae

Stramenopile Algae: Diatoms, Golden, Brown

Stramenopile algae include diatoms, golden algae, and brown algae. These phototrophic microorganisms have flagella with many short, hairlike extensions. That feature gave the group its name, which comes from Latin words meaning “straw” and “hair.” Diatoms are unicellular, photosynthetic eukaryotes, and more than 200 genera are known. They are important parts of plankton in both marine and freshwater ecosystems. Their most distinctive feature is a silica-based cell wall called a frustule. This...

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 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: 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...

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

Explore Excavata protists, including diplomonads, parabasalids, kinetoplastids, and euglenids, and learn how their structures fit their habitats and lifestyles.

Excavata Protists and Their Adaptations | 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

Excavata Protists and Their Adaptations

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