Name: deep sea microbes and extreme conditions
Uploaded: 2026-03-12T13:57:45.000Z
Duration: 1 min 18 s
Channel: JoVE

Les profondeurs marines, à des profondeurs supérieures à 1 000 mètres, sont marquées par des températures froides de 2 à 3 degrés Celsius, une immense pression hydrostatique augmentant d’environ 1 atmosphère tous les 10 mètres, et de faibles niveaux de nutriments.Les microbes piézotolérants sont ceux qui peuvent tolérer des conditions de haute pression et rester viables sous celles-ci, comme les membres du genre Colwellia.En revanche, les véritables piézophiles, comme les espèces de Moritella , croissent et survivent mieux sous haute pression grâce à des mécanismes cellulaires spécifiques.Par exemple, pour maintenir la fluidité des membranes et la stabilité des protéines sous haute pression, les piézophiles augmentent la proportion d’acides gras insaturés dans leurs membranes. Certaines espèces expriment des protéines régulées par la pression telles que l’OmpH via des systèmes de transcription sensibles à la pression.En dessous de 2 000 mètres, les sédiments abritent des réducteurs de sulfates et des organismes oxydant le méthane, ainsi que d’autres microbes adaptés à une limitation énergétique extrême.Cette rareté entraîne des densités cellulaires bien plus faibles que dans les régions moins profondes.

deep sea microbial ecology

Deep Sea Microbial Ecology

L&#x27;oc&#xE9;an profond et les s&#xE9;diments sous-jacents repr&#xE9;sentent de vastes habitats microbiens, encore largement inexplor&#xE9;s, qui s&#x27;&#xE9;tendent bien au-del&#xE0; de la zone photique &#xE9;clair&#xE9;e par le soleil. La zone photique (euphotique) s&#x27;&#xE9;tend g&#xE9;n&#xE9;ralement sur les ~100 &#xE0; 200 premiers m des eaux p&#xE9;lagiques de l&#x27;oc&#xE9;an ouvert, mais sa profondeur varie selon les r&#xE9;gions g&#xE9;ographiques et les saisons, l&#xE0; o&#xF9; la lumi&#xE8;re est suffisante pour soutenir la vie photosynth&#xE9;tique. En dessous se trouvent les grands fonds, s&#x27;&#xE9;tendant approximativement de 1 000 &#xE0; 6 000 m (des zones bathyp&#xE9;lagiques aux zones abyssales), avec des fosses hadales plus profondes s&#x27;&#xE9;tendant au-del&#xE0; de 6 000 m&#xE8;tres. Cette r&#xE9;gion est caract&#xE9;ris&#xE9;e par une obscurit&#xE9; totale, des temp&#xE9;ratures tr&#xE8;s froides (2 &#xE0; 3 &#xB0;C, pouvant &#xEA;tre l&#xE9;g&#xE8;rement plus &#xE9;lev&#xE9;es au niveau des sources hydrothermales), une pression hydrostatique &#xE9;lev&#xE9;e qui augmente depuis la surface d&#x27;environ ~101,33 Kpa par 10 m (par exemple, ~10,13 Mpa &#xE0; 1 000 m), et de s&#xE9;v&#xE8;res limitations en nutriments.
Les micro-organismes qui peuplent ces profondeurs pr&#xE9;sentent des adaptations physiologiques uniques. Certains, comme les microbes pi&#xE9;zotol&#xE9;rants, peuvent tol&#xE9;rer des pressions &#xE9;lev&#xE9;es mais leur croissance est optimale &#xE0; 101,33 Kpa. D&#x27;autres, appel&#xE9;s pi&#xE9;zophiles, se d&#xE9;veloppent mieux sous haute pression, g&#xE9;n&#xE9;ralement autour de 30,40 &#xE0; 40,53 Mpa, et des pi&#xE9;zophiles extr&#xEA;mes comme Moritella spp. de la fosse des Mariannes n&#xE9;cessitent des pressions sup&#xE9;rieures &#xE0; 70,93 Mpa pour cro&#xEE;tre. Pour s&#x27;adapter, ces organismes d&#xE9;veloppent plusieurs processus cellulaires uniques, comme l&#x27;augmentation de la proportion d&#x27;acides gras insatur&#xE9;s afin de maintenir la fluidit&#xE9; membranaire sous pression, et l&#x27;expression de prot&#xE9;ines sensibles &#xE0; la pression comme OmpH.
Sous le plancher oc&#xE9;anique, la vie microbienne se poursuit dans les s&#xE9;diments des grands fonds, formant l&#x27;une des plus vastes biosph&#xE8;res microbiennes de la Terre. La densit&#xE9; microbienne des s&#xE9;diments diminue avec la profondeur, passant d&#x27;environ 10&#x2079; cellules/g en surface &#xE0; moins de 10&#xB3; cellules/g &#xE0; plusieurs centaines de m&#xE8;tres de profondeur. Cette diminution correspond &#xE0; une r&#xE9;duction de la disponibilit&#xE9; &#xE9;nerg&#xE9;tique due &#xE0; l&#x27;&#xE9;puisement de la mati&#xE8;re organique et des accepteurs terminaux d&#x27;&#xE9;lectrons tels que le sulfate. Dans les marges continentales riches en nutriments, le sulfate est rapidement consomm&#xE9;, c&#xE9;dant la place &#xE0; la m&#xE9;thanogen&#xE8;se. En revanche, dans les s&#xE9;diments oc&#xE9;aniques profonds pauvres en mati&#xE8;re organique, le sulfate peut persister jusqu&#x27;au socle basaltique.
Malgr&#xE9; de faibles densit&#xE9;s cellulaires, l&#x27;immense volume de s&#xE9;diments abrite environ 5.4 &#xD7; 10&#xB2;&#x2079; cellules procaryotes. Le m&#xE9;tabolisme microbien dans ces zones repose sur la mati&#xE8;re organique lentement d&#xE9;gradable et sur des compos&#xE9;s produits g&#xE9;ochimiquement tels que le m&#xE9;thane, l&#x27;hydrog&#xE8;ne et l&#x27;ac&#xE9;tate. Les &#xE9;tudes phylog&#xE9;n&#xE9;tiques r&#xE9;v&#xE8;lent une dominance d&#x27;arch&#xE9;es non cultiv&#xE9;es, notamment les Bathyarchaeota, et de prot&#xE9;obact&#xE9;ries sulfato-r&#xE9;ductrices, qui s&#x27;adaptent toutes &#xE0; des limitations &#xE9;nerg&#xE9;tiques extr&#xEA;mes gr&#xE2;ce &#xE0; une croissance lente, des g&#xE9;nomes compacts et des voies ana&#xE9;robies sp&#xE9;cialis&#xE9;es.

The deep ocean and its underlying sediments represent vast, largely unexplored microbial habitats that extend far beyond the sunlit photic zone. The ...

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Education

Enseignement

JoVE Core

Microbiology

Microbiologie

Unit

Unité

Microbial Ecology

Écologie microbienne

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

deep sea microbes and extreme conditions

Deep sea microbes live in one of Earth’s harshest environments. The deep ocean is far below the sunlit photic zone, which usually reaches the upper 100 to 200 meters of open water. Below that layer, the bathypelagic and abyssal zones stretch from about 1,000 to 6,000 meters, and hadal trenches go even deeper.

This region is dark, cold, and highly pressurized. Temperatures are usually around 2 to 3°C, although hydrothermal vents can be slightly warmer. Pressure rises by about 1 atmosphere for every 10 meters of depth, so it reaches about 100 atmospheres at 1,000 meters. Nutrients are also scarce, which makes life difficult for microbes.

Some deep sea microorganisms are piezotolerant. This means they can handle high pressure but still grow best at 1 atmosphere. Others are piezophiles, which grow best under high pressure, often around 300 to 400 atmospheres. Extreme piezophiles, such as Moritella species from the Mariana Trench, need pressures above 700 atmospheres to grow.

These microbes survive through special cell changes. Many increase the amount of unsaturated fatty acids in their membranes so the membranes stay fluid under pressure. Some also express pressure-sensitive proteins such as OmpH. These adaptations help cells function in conditions that would damage most surface-dwelling life.

Life also continues beneath the seafloor in deep-sea sediments. This subsurface habitat is one of the largest microbial biospheres on Earth. Microbial density drops with depth, from about 10^9 cells per gram near the surface to fewer than 10^3 cells per gram at hundreds of meters down.

That decline reflects lower energy supply. Organic matter becomes depleted, and terminal electron acceptors such as sulfate are used up. On nutrient-rich continental margins, sulfate disappears quickly and methanogenesis begins. In organic-poor deep-ocean sediments, sulfate can remain all the way to the basaltic basement.

Even with very low cell numbers, the total sediment volume is enormous. It may contain an estimated 5.4 × 10^29 prokaryotic cells. These microbes use slowly degradable organic matter and compounds made geochemically, including methane, hydrogen, and acetate.

Many of the organisms found there are still uncultured. Phylogenetic studies often show Archaea, including Bathyarchaeota, and sulfate-reducing Proteobacteria. They are adapted to extreme energy limits through slow growth, compact genomes, and specialized anaerobic pathways.

Deep Sea Microbes and Extreme Conditions

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key terms and concepts

Explore how deep sea microbes survive cold, dark, high-pressure waters and nutrient-poor sediments through special adaptations and slow metabolism.

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microbiology

Deep Sea Microbes and Extreme Conditions

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