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

Excavata é um grupo diversificado de protistas, incluindo espécies quimioorganotróficas e fototróficas. Os grupos-chave incluem diplomonadas, parabasalídeos e euglenozoários. Diplomonadas como Giardia são caracterizadas por dois núcleos e mitossomos, que são mitocôndrias subdesenvolvidas incapazes de produção de ATP. Parabasalídeos são espécies anaeróbicas com corpo parabasal. Trichomonas é um exemplo proeminente, sem mitocôndrias, mas contendo hidrogenossomos, que geram ATP com gás hidrogênio como subproduto. Os euglenozoários são espécies móveis com a capacidade de funcionar como quimiotróficos e fototróficos. A maioria das espécies normalmente tem dois flagelos, mas apenas um é visível externamente, emergindo de uma bolsa flagelar anterior. O exemplo representativo, Euglena, exibe mixotrofia. Ele prospera na presença de luz, mas um longo período de escuridão pode fazer com que ele perca seus cloroplastos e mude para um modo quimioorganotrófico de metabolismo.

diversidade de protozoários

Diversity of Protists I

Excavata &#233; um grupo diverso de protistas que inclui esp&#233;cies quimio-organotr&#243;ficas e fototr&#243;ficas, com algumas capazes de prosperar em ambientes anaer&#243;bicos. Entre os principais grupos dentro de Excavata est&#227;o os diplomon&#225;didos e os parabasal&#237;deos, protistas flagelados que n&#227;o possuem mitoc&#244;ndrias nem cloroplastos. Esses microrganismos habitam, em geral, ambientes an&#243;xicos, como os intestinos de animais, onde existem em forma simbi&#243;tica ou como parasitas, dependendo da fermenta&#231;&#227;o para a produ&#231;&#227;o de energia. Alguns diplomon&#225;didos s&#227;o respons&#225;veis por doen&#231;as significativas em peixes, animais dom&#233;sticos e humanos, enquanto uma esp&#233;cie de parabasal&#237;deo &#233; a causa de uma importante doen&#231;a sexualmente transmiss&#237;vel em humanos. Ambos os grupos compartilham um ancestral comum relativamente recente, antes de divergirem em linhagens evolutivas separadas.
Os diplomon&#225;didos se caracterizam pela presen&#231;a de dois n&#250;cleos de tamanho igual e pela posse de mitossomos &#8212; mitoc&#244;ndrias altamente reduzidas que carecem de prote&#237;nas da cadeia de transporte de el&#233;trons e enzimas associadas ao ciclo do &#225;cido c&#237;trico. Um membro importante desse grupo, Giardia, possui um genoma relativamente pequeno e compacto, com poucos &#237;ntrons e aus&#234;ncia de genes codificadores de vias metab&#243;licas relacionadas ao ciclo do &#225;cido c&#237;trico. Essas caracter&#237;sticas gen&#233;ticas est&#227;o alinhadas com seu estilo de vida parasit&#225;rio e anaer&#243;bico. A esp&#233;cie Giardia intestinalis, tamb&#233;m conhecida como Giardia lamblia, &#233; respons&#225;vel pela giard&#237;ase, uma doen&#231;a diarreica transmitida pela &#225;gua e comum nos Estados Unidos.
Os parabasal&#237;deos possuem uma estrutura distinta chamada corpo parabasal, que oferece suporte estrutural ao complexo de Golgi. Esses protistas anaer&#243;bicos n&#227;o possuem mitoc&#244;ndrias, mas cont&#234;m hidrogenossomos, que desempenham um papel no metabolismo energ&#233;tico. Os parabasal&#237;deos s&#227;o comumente encontrados nos tratos intestinal e urogenital de vertebrados e invertebrados, onde atuam como parasitas ou simbiontes comensais. Um exemplo de destaque &#233; Trichomonas vaginalis, um organismo flagelado que causa uma infec&#231;&#227;o sexualmente transmiss&#237;vel amplamente disseminada em humanos. Os genomas dos parabasal&#237;deos exibem uma estrutura &#250;nica entre os eucariontes, pois geralmente carecem de &#237;ntrons. O genoma de T. vaginalis &#233; particularmente grande para um organismo parasita, com cerca de 160 milh&#245;es de pares de bases. Tamb&#233;m apresenta evid&#234;ncias de transfer&#234;ncia horizontal de genes a partir de bact&#233;rias e &#233; altamente repetitivo, com in&#250;meros elementos transpon&#237;veis, o que dificulta a an&#225;lise gen&#244;mica. Apesar dessas complexidades, estima-se que T. vaginalis possua cerca de 60.000 genes &#8212; quase o dobro do n&#250;mero encontrado no genoma humano &#8212; sendo um dos maiores genomas eucari&#243;ticos conhecidos.
Os cinetoplast&#237;deos representam outro grupo importante dentro de Excavata, nomeados pelo cinetoplasto &#8212; uma massa densa de DNA localizada dentro de uma &#250;nica mitoc&#244;ndria de grandes dimens&#245;es. Esses organismos habitam principalmente ambientes aqu&#225;ticos, onde consomem bact&#233;rias, embora algumas esp&#233;cies sejam parasit&#225;rias e causem doen&#231;as graves em humanos e animais. O g&#234;nero Trypanosoma inclui pat&#243;genos que infectam humanos, como Trypanosoma brucei, respons&#225;vel pela doen&#231;a do sono africana. Essa doen&#231;a cr&#244;nica e geralmente fatal progride do sangue para o sistema nervoso central, causando inflama&#231;&#227;o cerebral e medular, com sintomas neurol&#243;gicos subsequentes. O parasita &#233; transmitido pela mosca ts&#233;-ts&#233; (Glossina), um inseto hemat&#243;fago nativo de certas regi&#245;es da &#193;frica. Uma vez dentro da mosca, o parasita prolifera no trato intestinal e migra para as gl&#226;ndulas salivares, de onde pode ser transmitido a um novo hospedeiro humano por meio de uma picada.
Outros parasitas cinetoplast&#237;deos que afetam humanos incluem Trypanosoma cruzi, causador da doen&#231;a de Chagas, e esp&#233;cies de Leishmania, respons&#225;veis pela leishmaniose. A doen&#231;a de Chagas &#233; transmitida pela picada de um inseto hemat&#243;fago conhecido como &#8220;barbeiro&#8221;. Embora frequentemente autolimitada, a doen&#231;a pode evoluir para uma condi&#231;&#227;o cr&#244;nica e potencialmente fatal. A leishmaniose, encontrada em regi&#245;es tropicais e subtropicais, &#233; transmitida pelo flebotom&#237;neo e pode se manifestar como infec&#231;&#245;es cut&#226;neas localizadas ou como uma doen&#231;a sist&#234;mica que afeta o ba&#231;o e o f&#237;gado, podendo ser fatal.
Os euglen&#237;deos, outro grupo bem estudado dentro de Excavata, distinguem-se por sua natureza n&#227;o patog&#234;nica e pela capacidade de atuarem tanto como quimi&#243;trofos quanto como fot&#243;trofos. Esses eucariontes microbianos m&#243;veis s&#227;o, em sua maioria, protistas n&#227;o patog&#234;nicos e podem funcionar como fot&#243;trofos e heter&#243;trofos. A maioria possui dois flagelos que emergem de uma bolsa flagelar anterior, embora apenas um seja vis&#237;vel externamente, o que lhes permite navegar entre ambientes iluminados e escuros, apoiando suas estrat&#233;gias nutricionais flex&#237;veis. Os euglen&#237;deos s&#227;o comumente encontrados em habitats aqu&#225;ticos, tanto de &#225;gua doce quanto marinhos, e muitas esp&#233;cies cont&#234;m cloroplastos que possibilitam o crescimento fototr&#243;fico. No entanto, na aus&#234;ncia de luz, c&#233;lulas de Euglena, um representante dos euglen&#237;deos, podem perder seus cloroplastos e mudar para um modo de metabolismo quimio-organotr&#243;fico. Al&#233;m disso, muitos euglen&#237;deos s&#227;o capazes de realizar fagocitose &#8212; um processo no qual englobam c&#233;lulas bacterianas envolvendo-as com sua membrana citoplasm&#225;tica flex&#237;vel, permitindo a digest&#227;o interna.

Diversidade de protozoários

Excavata &#233; um grupo diverso de protistas que inclui esp&#233;cies quimio-organotr&#243;ficas e fototr&#243;ficas, com algumas capazes de prosperar em ...

Education

JoVE Core

Microbiology

Microbiologia

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Microbial Diversity

Diversidade Microbiana

KEY TERMS AND CONCEPTS

TERMOS E CONCEITOS-CHAVE

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

three-domain system of life

How rRNA Reshaped Life's Domains

Ribosomal RNA, or rRNA, changed how scientists classify life. Sequence analysis showed three major groups of cells: eukaryotes, bacteria, and archaea. In 1978, Carl R. Woese proposed domains as a taxonomic level above kingdoms to separate these groups. Woese also showed that archaea and bacteria are not the same, even though they can look similar. The three domains differ in rRNA, membrane lipid structure, transfer RNA, and sensitivity to antibiotics. These differences helped scientists build...

microbial classification system

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methods of classification and identification

methods-of-classification-and-identification

Bacterial ID Through Lab Tests

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modern molecular taxonomy

DNA Tools for Identifying Bacteria

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applications of molecular taxonomy

Molecular Taxonomy in Bacterial Research

Molecular taxonomy in bacterial research uses DNA sequencing and DNA fingerprinting to classify bacteria more precisely. These molecular tools help scientists study bacterial diversity, evolutionary relationships, and ecological roles. They have changed how researchers identify and compare bacteria in both health and environmental studies. One major use of molecular taxonomy is resolving taxonomic ambiguities, or unclear classification cases. It can separate closely related bacteria that were...

bacterial phylum proteobacteria

Proteobacteria Classes and Their Key Roles

Proteobacteria are a large and diverse phylum of Gram-negative bacteria. They have an outer membrane that contains lipopolysaccharides. Many of them use different ways to get energy, including phototrophy, chemolithotrophy, and heterotrophy. They live in soil, water, and host-associated environments. This phylum is divided into six classes: Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, Epsilonproteobacteria, and Zetaproteobacteria. Each class includes...

bacterial phylum chlamydiae

Chlamydiae Life Cycle and Host Infection

Chlamydiae are bacteria that live inside eukaryotic host cells. The phylum Chlamydiae, also called Chlamydiota, contains a single order, Chlamydiales. These bacteria are obligate intracellular parasites, which means they must enter host cells to survive and grow. Members of this group are usually very small cocci, about 0.5 μm across. They also have reduced genomes, usually between 0.55 and 1 Mbp. This limited genome fits their highly specialized way of life and their dependence on host...

bacterial phylum planctomycetes 

Planctomycetes Cell Structure and Life Cycle

Planctomycetes are a group of gram-negative bacteria known for unusual cell structures and a distinctive life cycle. They are mainly placed in two orders, Planctomycetales and Brocadiales. Many cells show stalks or other appendages and often appear in rosette groups. A key feature of these bacteria is their cell envelope. Planctomycetes have an S-layer, a surface layer that is relatively uncommon in bacteria. They also divide by budding, which is different from the simple cell split seen in...

bacterial phylum verrucomicrobiota

Verrucomicrobiota Cell Structure and Traits

Verrucomicrobiota are a bacterial phylum with several recognized orders, and most species belong to Verrucomicrobiotales. Many members are aerobic or facultatively aerobic, which means they can use oxygen but may also grow without it. They can also ferment sugars. One exception is the genus Methylacidiphilum, which contains aerobic methanotrophs, bacteria that use methane and oxygen. These bacteria live in many different places. They are found in freshwater, marine habitats, forest soils, and...

bacterial phylum spirochaetes

Spirochete Shape, Motion, and Disease

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bacterial phylum cyanobacteria

Cyanobacteria and Oxygenic Photosynthesis

Cyanobacteria are oxygenic, phototrophic bacteria that helped change Earth&amp;#8217;s atmosphere from low in oxygen to oxygen-rich billions of years ago. They are also very diverse in shape and size. Some are unicellular, while others grow as filaments. Cell size can range from 0.5 µm to 100 µm. Scientists group cyanobacteria into five major types. Chroococcales are unicellular and divide by binary fission. Pleurocapsales are also unicellular, but they divide by multiple fission.

bacterial phylum actinobacteria

Actinobacteria: Soil Bacteria and Cheese

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bacterial phylum firmicutes

Firmicutes: Bacteria, Fermentation, and Spores

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bacterial phylum bacteroidota

Gut and Environment Bacteria in Bacteroidota

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anoxygenic phototrophic bacteria

Sulfur-Using Bacteria That Harvest Light

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hyperthermophilic bacteria

Heat-Loving Bacteria and Their Enzymes

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bacterial phylum tenericutes

Mycoplasmas and Wall-Less Bacteria

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other unique bacteria

Magnetotactic and DNA-Resistant Bacteria

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overview of archaea

Archaea Cell Structure and Metabolism

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diversity of archaea i

Archaea Extremes: Euryarchaeota

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diversity of archaea ii

New Archaea Phyla and Their Roles

Archaea are one of the three domains of life, and their diversity includes species that live in both extreme and moderate environments. For a long time, most known archaea were grouped into two major phyla: Euryarchaeota and Crenarchaeota. Recent molecular studies have added three more phyla to this picture: Thaumarchaeota, Nanoarchaeota, and Korarchaeota. Thaumarchaeota are mesophilic archaea, which means they live in moderate conditions. They are found in soils, lakes, and marine regions. A...

diversity of archaea iii

Crenarchaeota in Extreme Hot Springs

Crenarchaeota are a major group of Archaea known for living in extreme heat and acidity. They are found in sulfur-rich hot springs, volcanic systems, and submarine hydrothermal vents. Many of these habitats reach temperatures above 100°C. Their survival in these conditions gives clues about life on early Earth. Crenarchaeota also show a wide range of cell shapes. Some form filaments, while others have irregular discs or lobed cocci, which are round cells with lobes. Scientists place them in...

diversity of archaea iv

How Hyperthermophilic Archaea Survive Heat

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overview of fungi

Fungi Structure, Reproduction, and Roles

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fungal group zygomycota

Zygomycota: Spores, Hyphae, and Roles

Zygomycota are a former fungal group made up mostly of terrestrial molds that act as decomposers. Recent phylogenetic studies now place them in two major clades: Mucoromycota and Zoopagomycota. Mucoromycota includes many symbiotic species, while Zoopagomycota is made up mainly of parasitic and pathogenic fungi. These fungi have coenocytic hyphae, which are filaments without septa, or cross walls. That structure allows cytoplasm and organelles to move through the hyphae in one continuous stream.

fungal phylum microsporidia

Microsporidia Spores and Host Infection

Microsporidia are unicellular fungi that live as obligate intracellular parasites. They were first classified as protists, but phylogenetic, molecular, and structural evidence later linked them to the Chytridiomycota. These non-motile organisms infect many animal hosts, including humans, and depend heavily on the host cell to survive. Their cells are very small, usually 2 to 5 micrometers wide. Microsporidia form spores with a chitin shell, which helps them resist the outside environment. The...

fungal phylum ascomycota

Ascomycota: Sac Fungi and Their Spore Cycle

Ascomycota are sac fungi with a wide range of forms and roles. This fungal phylum includes unicellular yeasts and filamentous molds such as Aspergillus and Penicillium. They live in aquatic and terrestrial habitats and have major ecological and economic importance. A key feature of ascomycetes is the ascus, a sac-like structure that contains haploid ascospores. These fungi can reproduce sexually and asexually. Sexual reproduction starts with plasmogamy, the fusion of cytoplasm from two...

fungal phylum basidiomycota

Basidiomycota: Mushrooms, Spores, and Ecological Roles

Basidiomycota is a major group of fungi that includes mushrooms, puffballs, decomposers, symbionts, plant pathogens, and some edible species. These fungi matter in ecosystems, agriculture, and medicine. A key feature of this phylum is the basidium, a small club-shaped structure that makes basidiospores. Many basidiomycetes form visible fruiting bodies called basidiocarps. The life cycle starts when a haploid basidiospore germinates into monokaryotic mycelium. When two compatible mycelia fuse,...

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,...

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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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