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

Domänenbakterien enthalten einige Spezies mit außergewöhnlichen Eigenschaften, insbesondere magnetische und strahlenresistente Bakterien. Magnetische Bakterien, wie Magnetospirillum magnetotacticum und Desulfovibrio magneticus, sind typischerweise in der Nähe der oxisch-anoxischen Grenzfläche von geschichteten Seen zu finden. Diese Bakterienarten besitzen Magnetosomen. Ein Magnetosom besteht typischerweise aus Ketten von Teilchen, die entweder aus Magnetit (bei aeroben Spezies) oder aus Greigit (bei anaeroben Spezies) bestehen. Diese Bakterien weisen eine Magnetotaxis auf. Ihre Magnetosomen richten sich sowohl in der nördlichen als auch in der südlichen Hemisphäre nach dem Erdmagnetfeld aus und leiten sie zu den oxisch-anoxischen Übergangszonen. Die Strahlungsbeständigkeit ist eine bemerkenswerte Eigenschaft, die von Mitgliedern der Ordnung der Deinococcales gezeigt wird. Die Spezies Deinococcus radiodurans kann Dosen von 15.000 Gray ionisierender Strahlung überleben. Die einzigartige toroidale Anordnung der DNA innerhalb der Zelle und eine mehrschichtige Zellwandstruktur spielen eine Schlüsselrolle für die Strahlenbeständigkeit.

früh abgezweigte phyla der bakterien

Other Unique Bacteria

Magnetische Bakterien zeigen eine gerichtete Bewegung namens Magnetotaxis, die durch Strukturen namens Magnetosomen gesteuert wird. Diese Magnetosomen bestehen aus Ketten magnetischer Partikel aus entweder Magnetit (Fe_3O_4) oder Greigit (Fe_3S_4) und sind in einer linearen Konformation organisiert, die durch ein Protein-Ger&#252;st innerhalb von Einst&#252;lpungen der Zellmembran stabilisiert wird. Die Bakterien richten sich entlang der magnetischen Nord-S&#252;d-Feldlinien aus, &#228;hnlich wie eine Kompassnadel. Sie sind typischerweise mikroaerophil oder anaerob und werden h&#228;ufig an der oxisch-anoxischen Grenzschicht in Sedimenten oder geschichteten Seen gefunden. Aerobe Arten enthalten in der Regel Magnetit in ihren Magnetosomen, w&#228;hrend anaerobe Arten Greigit enthalten.
Die &#246;kologische Rolle der bakteriellen Magnetosomen ist noch unklar, doch k&#246;nnten sie einen selektiven Vorteil bieten, indem sie die Bakterien in sauerstoffarme Zonen halten. Der Sauerstoffgehalt nimmt in Sedimenten und geschichteten Seen mit zunehmender Tiefe typischerweise ab. Da das Erdmagnetfeld in beiden Hemisph&#228;ren eine starke vertikale Komponente aufweist, richten sich magnetotaktische Bakterien entlang dieser Feldlinien aus, um nach unten zu schwimmen, weg vom Sauerstoff. Das Magnetosom fungiert dabei wie ein Kompass, w&#228;hrend die Flagellenbewegung durch eine chemotaktische Reaktion auf Sauerstoff gesteuert wird.
Magnetische Bakterien zeigen unterschiedliche magnetische Polarit&#228;ten in Abh&#228;ngigkeit von der Orientierung ihrer Magnetosomen. In der n&#246;rdlichen Hemisph&#228;re bewegen sich nordw&#228;rts ausgerichtete Bakterien nach unten, w&#228;hrend sich in der s&#252;dlichen Hemisph&#228;re s&#252;dw&#228;rts ausgerichtete Bakterien ebenfalls nach unten bewegen.
Die meisten magnetischen Bakterien geh&#246;ren zu den Alphaproteobakterien, jedoch wurden auch Arten bei den Gammaproteobakterien, Deltaproteobakterien und der Nitrospira-Gruppe gefunden. Eine gut charakterisierte Art, Magnetospirillum magnetotacticum, ist ein chemoorganotropher Mikroaerophiler, der auch unter anaeroben Bedingungen durch Reduktion von Nitrat (NO_3^-) oder Lachgas (N_2O) wachsen kann. Eine weitere Art, Desulfovibrio magneticus, ist ein obligat anaerober, sulfatreduzierender Organismus. Magnetosomen wurden auch bei Schwefeloxidierern und Nichtschwefelpurpurbakterien beobachtet.
Dar&#252;ber hinaus existieren mehrzellige magnetotaktische Bakterien. Diese Deltaproteobakterien bilden Aggregate von 10&#8211;20 Zellen, die in einer hohlen Kugel angeordnet sind. Obwohl bekannt ist, dass sie obligate Anaerobier sind, sind ihre genauen Stoffwechselwege bislang weiter unbekannt.
Deinococcus radiodurans, ein Mitglied der Deinococcales, ist hochresistent gegen&#252;ber Strahlung und Austrocknung und &#252;bersteht Dosen von 15.000 Gy. Es erscheint h&#228;ufig rot oder rosa aufgrund von Carotinoiden und wird aus Boden, Fleisch, Staub und Luft isoliert. Obwohl es gegen&#252;ber den meisten Mutagenen resistent ist, ist es anf&#228;llig f&#252;r DNA-Deletionen.
Sein einzigartiges DNA-Reparatursystem umfasst mehrere Enzyme, die eine effiziente Erholung von Strahlensch&#228;den erm&#246;glichen. D. radiodurans organisiert seine DNA in einer toroidalen Struktur, die die homologe Rekombination erleichtert und es erm&#246;glicht, fragmentierte Chromosomen wieder zusammenzusetzen. Diese au&#223;ergew&#246;hnliche Reparaturf&#228;higkeit erlaubt es der Zelle, nach extremer DNA-Sch&#228;digung das Wachstum und die Zellteilung wieder aufzunehmen.

Früh abgezweigte Phyla der Bakterien

Magnetische Bakterien zeigen eine gerichtete Bewegung namens Magnetotaxis, die durch Strukturen namens Magnetosomen gesteuert wird. Diese Magnetosomen ...

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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

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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...

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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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