Name: magnetotactic and dna-resistant bacteria
Uploaded: 2025-07-28T10:50:19.000Z
Duration: 1 min 18 s
Channel: JoVE

Les bactéries du domaine contiennent certaines espèces aux propriétés extraordinaires, notamment les bactéries magnétiques et résistantes aux radiations. Les bactéries magnétiques, telles que Magnetospirillum magnetotacticum et Desulfovibrio magneticus, se trouvent généralement près de l’interface oxique-anoxique des lacs stratifiés. Ces espèces bactériennes possèdent des magnétosomes. Un magnétosome se compose généralement de chaînes de particules constituées soit de magnétite, chez les espèces aérobies, soit de greigite, chez les espèces anaérobies. Ces bactéries présentent une magnétotaxie. Leurs magnétosomes s’alignent sur le champ géomagnétique terrestre dans les hémisphères nord et sud, les guidant vers les zones de transition oxique-anoxique. La résistance aux radiations est une propriété remarquable présentée par les membres de l’ordre des Déinococcales. L’espèce Deinococcus radiodurans peut survivre à des doses de 15 000 grays de rayonnement ionisant. L’arrangement toroïdal unique de son ADN à l’intérieur de la cellule et une structure de paroi cellulaire multicouche jouent un rôle clé dans la résistance aux radiations.

bactéries profondément ramifiées

Other Unique Bacteria

Les bact&#233;ries magn&#233;tiques pr&#233;sentent un mouvement dirig&#233; appel&#233; magn&#233;totaxie, rendu possible par des structures appel&#233;es magn&#233;tosomes. Ces magn&#233;tosomes consistent en des cha&#238;nes de particules magn&#233;tiques compos&#233;es de magn&#233;tite (Fe_3O_4) ou de gr&#233;igite (Fe_3S_4), organis&#233;es en conformation lin&#233;aire gr&#226;ce &#224; un &#233;chafaudage prot&#233;ique situ&#233; dans des invaginations de la membrane cellulaire. Les bact&#233;ries s&#8217;alignent le long des lignes du champ magn&#233;tique nord&#8211;sud, &#224; la mani&#232;re d&#8217;une aiguille de boussole. Elles sont typiquement microa&#233;rophiles ou ana&#233;robies, et se trouvent fr&#233;quemment &#224; l&#8217;interface oxyque&#8211;anoxyque des s&#233;diments ou des lacs stratifi&#233;s. Les esp&#232;ces a&#233;robies contiennent g&#233;n&#233;ralement de la magn&#233;tite, tandis que les esp&#232;ces ana&#233;robies renferment de la gr&#233;igite.
Le r&#244;le &#233;cologique des magn&#233;tosomes bact&#233;riens reste incertain, mais il pourrait offrir un avantage s&#233;lectif en maintenant les bact&#233;ries dans des zones pauvres en oxyg&#232;ne. Le niveau d&#8217;oxyg&#232;ne diminue g&#233;n&#233;ralement avec la profondeur dans les s&#233;diments et les lacs stratifi&#233;s. &#201;tant donn&#233; que le champ magn&#233;tique terrestre poss&#232;de une forte composante verticale dans les deux h&#233;misph&#232;res, les bact&#233;ries magn&#233;totactiques s&#8217;alignent sur ces lignes pour nager vers le bas, &#224; l&#8217;&#233;cart de l&#8217;oxyg&#232;ne. Le magn&#233;tosome agit comme une boussole, tandis que le mouvement flagellaire est contr&#244;l&#233; par une r&#233;ponse chimiotactique &#224; l&#8217;oxyg&#232;ne.
Les bact&#233;ries magn&#233;tiques montrent diff&#233;rentes polarit&#233;s magn&#233;tiques selon l&#8217;orientation de leurs magn&#233;tosomes. Dans l&#8217;h&#233;misph&#232;re nord, les bact&#233;ries attir&#233;es vers le nord se d&#233;placent vers le bas, tandis que dans l&#8217;h&#233;misph&#232;re sud, ce sont les bact&#233;ries attir&#233;es vers le sud qui adoptent ce comportement.
La plupart des bact&#233;ries magn&#233;tiques appartiennent aux Alphaproteobacteria, mais des esp&#232;ces ont &#233;galement &#233;t&#233; identifi&#233;es chez les Gammaproteobacteria, les Deltaproteobacteria et le groupe Nitrospira. Une esp&#232;ce bien caract&#233;ris&#233;e, Magnetospirillum magnetotacticum, est un microa&#233;rophile chimioorganotrophe capable de cro&#238;tre en ana&#233;robiose par r&#233;duction du nitrate (NO_3^-) ou de l&#8217;oxyde nitreux (N_2O). Une autre esp&#232;ce, Desulfovibrio magneticus, est un ana&#233;robie strict r&#233;ducteur de sulfate. Des magn&#233;tosomes ont &#233;galement &#233;t&#233; observ&#233;s chez des bact&#233;ries oxydant le soufre ou chez des bact&#233;ries phototrophes non sulfureuses.
Il existe aussi des bact&#233;ries magn&#233;totactiques multicellulaires. Ces Deltaproteobacteria forment des agr&#233;gats de 10 &#224; 20 cellules dispos&#233;es en sph&#232;re creuse. Bien qu&#8217;elles soient ana&#233;robies strictes, leurs voies m&#233;taboliques exactes restent inconnues.
Deinococcus radiodurans, membre des Deinococcales, est extr&#234;mement r&#233;sistant aux radiations et &#224; la dessiccation, survivant &#224; des doses allant jusqu&#8217;&#224; 15 000 Gy. Elle pr&#233;sente souvent une couleur rouge ou rose en raison des carot&#233;no&#239;des et est isol&#233;e de sols, de viandes, de poussi&#232;res ou d&#8217;air. Bien qu&#8217;elle soit r&#233;sistante &#224; la plupart des mutag&#232;nes, elle reste sensible aux d&#233;l&#233;tions de l&#8217;ADN.
Son syst&#232;me unique de r&#233;paration de l&#8217;ADN fait intervenir de multiples enzymes, permettant une r&#233;cup&#233;ration efficace apr&#232;s des dommages dus aux radiations. D. radiodurans organise son ADN sous forme torique, ce qui facilite la recombinaison homologue et permet de r&#233;assembler des chromosomes fragment&#233;s. Cette capacit&#233; exceptionnelle de r&#233;paration permet &#224; la cellule de reprendre sa croissance et sa division m&#234;me apr&#232;s des dommages extr&#234;mes &#224; l&#8217;ADN.

Bactéries profondément ramifiées

Les bact&#233;ries magn&#233;tiques pr&#233;sentent un mouvement dirig&#233; appel&#233; magn&#233;totaxie, rendu possible par des structures ...

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Microbiologie

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Microbial Diversity

Diversité microbienne

KEY TERMS AND CONCEPTS

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magnetotactic and dna-resistant bacteria

Magnetotactic bacteria move using Earth’s magnetic field, and some bacteria are known for extreme DNA repair. These unusual microbes show two very different survival strategies. One uses magnetic particles to guide movement. The other can recover after severe radiation damage.

Magnetotaxis is the directed movement seen in magnetic bacteria. It depends on magnetosomes, which are chains of magnetic particles made of magnetite (Fe₃O₄) or greigite (Fe₃S₄). A protein scaffold keeps these particles lined up inside membrane folds, and the cells then align with north–south magnetic field lines like a compass needle.

These bacteria are usually microaerophilic or anaerobic, so they live where oxygen is low. They are common near the oxic–anoxic interface in sediments and stratified lakes, where oxygen levels drop with depth. Aerobic species usually contain magnetite in their magnetosomes, while anaerobic species usually contain greigite. The magnetosome may help keep the cells in low-oxygen zones.

Earth’s magnetic field has a strong vertical component in both hemispheres. That helps magnetotactic bacteria swim downward, away from oxygen. The magnetosome acts like a compass, while flagellar movement is guided by a chemotactic response to oxygen. These bacteria also show different magnetic polarities. In the Northern Hemisphere, north-seeking bacteria move downward, and in the Southern Hemisphere, south-seeking bacteria do the same.

Most magnetic bacteria belong to the Alphaproteobacteria, but some are found in the Gammaproteobacteria, Deltaproteobacteria, and Nitrospira group. Magnetospirillum magnetotacticum is a chemoorganotrophic microaerophile that can also grow without oxygen by reducing nitrate (NO₃⁻) or nitrous oxide (N₂O). Desulfovibrio magneticus is a sulfate-reducing obligate anaerobe. Magnetosomes have also been seen in sulfur oxidizers and purple nonsulfur bacteria, and multicellular magnetotactic bacteria also exist.

These multicellular magnetotactic bacteria are Deltaproteobacteria that form groups of 10 to 20 cells in a hollow sphere. They are obligate anaerobes, but their exact metabolism is still unknown. Another unusual bacterium, Deinococcus radiodurans, is famous for surviving radiation and drying out. It can survive doses of 15,000 Gy and is often red or pink because of carotenoids. It is found in soil, meat, dust, and air.

D. radiodurans is resistant to most mutagens, but it is vulnerable to DNA deletions. Its DNA repair system uses multiple enzymes to rebuild damaged DNA after radiation exposure. The cell also arranges its DNA in a toroidal, or ring-like, structure. This shape supports homologous recombination and helps fragmented chromosomes be put back together. As a result, the cell can resume growth and division after extreme DNA damage.

Magnetotactic and DNA-Resistant Bacteria

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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Microbial classification organizes bacteria and archaea into ranked groups based on shared traits and evolutionary relationships. Scientists use phenotypic similarities, which are visible or measurable traits, and genotypic data, which comes from genetic information. The result is a hierarchy that helps place each organism in a clear taxonomic order. The ranking system starts with species and moves upward through genus, family, order, class, and finally domain. A species can include one or...

methods of classification and identification

methods-of-classification-and-identification

Bacterial ID Through Lab Tests

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modern molecular taxonomy

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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

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bacterial phylum actinobacteria

Actinobacteria: Soil Bacteria and Cheese

Actinobacteria include several gram-positive bacteria that are common in soil and food production. This group includes coryneform bacteria, propionic acid bacteria, mycobacteria, and actinomycetes. Each group has a different shape, growth pattern, and role. Coryneform bacteria are aerobic, nonmotile rods that often look irregular, club-shaped, or V-shaped. Their V-shape comes from snapping division. In this process, the inner cell wall forms the cross-wall first, while the outer wall stays...

bacterial phylum firmicutes

Firmicutes: Bacteria, Fermentation, and Spores

Firmicutes are a diverse phylum of Gram-positive bacteria with low GC content in their genomes. They include both monoderm and diderm cell envelopes, which points to a complex evolutionary history. Their members show wide variation in shape, metabolism, and ecological role. Three major orders help show this diversity: Lactobacillales, Clostridiales, and Bacillales. Lactobacillales include lactic acid bacteria, which are fermentative organisms that make lactic acid as their main product. These...

bacterial phylum bacteroidota

Gut and Environment Bacteria in Bacteroidota

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anoxygenic phototrophic bacteria

Sulfur-Using Bacteria That Harvest Light

Anoxygenic phototrophic bacteria are light-harvesting bacteria that do not release oxygen during photosynthesis. They include purple sulfur bacteria, purple nonsulfur bacteria, green sulfur bacteria, green nonsulfur bacteria, heliobacteria, and Chloracidobacterium thermophilum. These groups belong to the Gammaproteobacteria, Alphaproteobacteria, Betaproteobacteria, Chlorobi, Chloroflexi, Firmicutes, and Acidobacteria lineages, and each group has its own habitat and way of using light. Purple...

hyperthermophilic bacteria

Heat-Loving Bacteria and Their Enzymes

Hyperthermophilic bacteria live in extreme heat and show unusual adaptations that help them survive. Several of these species come from the Domain Bacteria and are found in hot springs and hydrothermal vents. Their biology helps explain how life can function in very hot environments. Thermotoga species are rod-shaped, gram-negative, non-sporulating hyperthermophiles. They form a sheath-like outer layer called a toga. These bacteria ferment sugars or starch and produce lactate, acetate, carbon...

bacterial phylum tenericutes

Mycoplasmas and Wall-Less Bacteria

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other unique bacteria

Magnetotactic bacteria move using Earth’s magnetic field, and some bacteria are known for extreme DNA repair. These unusual microbes show two very different survival strategies. One uses magnetic particles to guide movement. The other can recover after severe radiation damage. Magnetotaxis is the directed movement seen in magnetic bacteria. It depends on magnetosomes, which are chains of magnetic particles made of magnetite (Fe₃O₄) or greigite (Fe₃S₄). A protein scaffold keeps these particles...

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

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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

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fungal phylum microsporidia

Microsporidia Spores and Host Infection

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fungal phylum ascomycota

Ascomycota: Sac Fungi and Their Spore Cycle

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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

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other algae

Stramenopile Algae: Diatoms, Golden, Brown

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overview of protists

Protist Diversity, Movement, and Survival

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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: 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 magnetotactic bacteria, magnetosomes, and how Deinococcus radiodurans repairs DNA after extreme radiation damage in this high school biology page.

Magnetotactic and DNA-Resistant Bacteria | 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

Magnetotactic and DNA-Resistant Bacteria

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