Name: microbial mats and oxygen gradients
Uploaded: 2026-03-12T13:57:45.000Z
Duration: 1 min 25 s
Channel: JoVE

Les tapis microbiens sont des assemblages de micro-organismes qui poussent sur des surfaces naturelles ou artificielles.Ces assemblages commencent généralement sous forme de biofilms minces, de seulement quelques micromètres d’épaisseur, et peuvent se développer en structures plus épaisses et stratifiées.Les tapis cyanobactériens dans les sources chaudes et les milieux salins présentent des structures biologiques nettement stratifiées.La lumière du jour favorise la photosynthèse dans les couches supérieures, dominées par les cyanobactéries et d’autres bactéries phototrophes, qui produisent de l’oxygène.Pendant ce temps, les couches anoxiques plus profondes contiennent des bactéries réductrices de sulfates qui produisent du sulfure d’hydrogène.Pendant la nuit, la photosynthèse et la production d’oxygène cessent, permettant à l’accumulation de sulfure d’hydrogène dans le tapis microbien.En revanche, les tapis chimiotrophes situés dans des sédiments profonds pauvres en oxygène se forment par l’oxydation du soufre des espèces de Thioploca .Ces bactéries possèdent de grandes vacuoles internes qui stockent du nitrate, qu’elles absorbent de l’eau de mer environnante.Ils glissent ensuite dans des zones anoxiques riches en sulfures, utilisant le nitrate stocké comme accepteur d’électrons pour oxyder le sulfure d’hydrogène.

tapis microbiens

Microbial Mats

Les communautés microbiennes formant des biofilms et des tapis représentent des écosystèmes complexes et structurés spatialement où les processus métaboliques sont stratifiés selon la lumière, l’oxygène et les gradients de nutriments. Les biofilms sont des stades de colonisation initiale, de seulement quelques millimètres d’épaisseur, tandis que les tapis microbiens matures peuvent atteindre une épaisseur à l’échelle du centimètre et présenter une organisation verticale complexe. Leur hétérogénéité structurelle et fonctionnelle permet aux micro-organismes d’occuper des niches écologiques distinctes à quelques millimètres de profondeur.Les tapis cyanobactériens présents dans les sources chaudes et les environnements hypersalins illustrent un schéma clair de stratification métabolique. Pendant la journée, les couches de surface, dominées par les cyanobactéries et d’autres bactéries phototrophes, s’engagent dans une photosynthèse oxygénée, augmentant les concentrations d’oxygène dans la zone photique. Cette activité soutient les processus aérobies dans les couches supérieures. En revanche, les couches plus profondes contiennent des bactéries réductrices de sulfate qui prospèrent en l’absence d’oxygène, dégradent la matière organique et produisent du sulfure d’hydrogène comme sous-produit métabolique. La nuit, la photosynthèse cesse, le taux d’oxygène diminue, et le sulfure d’hydrogène s’accumule et diffuse vers le haut, créant un environnement fortement réducteur dans tout le tapis.Au-delà des tapis de surface, certaines communautés microbiennes, telles que celles dominées par les espèces de Thioploca , prospèrent dans des sédiments profonds pauvres en oxygène. Ces bactéries filamenteuses oxydantes du soufre démontrent une adaptation métabolique unique : la capacité de stocker du nitrate dans de grandes vacuoles intracellulaires. Les cellules de thioploca absorbent le nitrate des couches sédimentaires oxygénées et supérieures et migrent vers des zones plus profondes et anoxiques riches en sulfure d’hydrogène. Ils oxydent le sulfure en utilisant du nitrate stocké comme accepteur d’électrons, couplant la séparation spatiale des donneurs et accepteurs d’électrons dans une stratégie métabolique verticalement mobile.Ces écosystèmes microbiens complexes et stratifiés illustrent la remarquable adaptabilité des micro-organismes à des conditions environnementales fluctuantes et extrêmes, guidant des processus biogéochimiques clés tant dans les environnements naturels que artificiels.

Tapis microbiens

Microbial communities forming biofilms and mats represent complex, spatially structured ecosystems where metabolic processes are stratified according to ...

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Education

Enseignement

JoVE Core

Microbiology

Microbiologie

Unit

Unité

Microbial Ecology

Écologie microbienne

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

microbial mats and oxygen gradients

Microbial mats are layered communities of microbes that grow in response to changes in light, oxygen, and nutrients. These ecosystems are highly organized, and different microorganisms live at different depths. Biofilms are the early stage of this growth and are only a few millimeters thick. Mature microbial mats can grow to centimeter scale and show clear vertical structure.

This layered arrangement lets microbes fill separate niches within a very small space. In cyanobacterial mats from hot springs and hypersaline environments, the top layers receive light and support oxygenic photosynthesis. Cyanobacteria and other phototrophic bacteria dominate this surface zone. Their photosynthesis raises oxygen levels in the photic zone and supports aerobic activity near the top of the mat.

Deeper layers have little or no oxygen. There, sulfate-reducing bacteria break down organic matter and produce hydrogen sulfide. At night, photosynthesis stops, oxygen falls, and hydrogen sulfide moves upward. The whole mat becomes a strongly reducing environment during this time.

Some microbial communities live below the surface in deep, oxygen-poor sediments. Thioploca species are a good example. These filamentous sulfur-oxidizing bacteria store nitrate in large intracellular vacuoles. They take nitrate from oxygenated sediment layers above, then move into deeper anoxic zones that contain hydrogen sulfide. There, they oxidize sulfide by using the stored nitrate as an electron acceptor.

These stratified microbial ecosystems show how microbes adapt to extreme and changing conditions. They also drive important biogeochemical processes in natural and artificial settings.

Microbial Mats and Oxygen Gradients

introduction to microbial ecology

Microbial Communities in Soil and Extremes

Microbial ecology looks at how microorganisms live, interact, and adapt in different ecosystems. It also shows how these tiny organisms help shape nutrient cycling, energy flow, and environmental balance. An ecosystem includes living parts and non-living parts, and microbes respond to both. Microorganisms can form populations, which are groups of the same species living together at the same time. When populations from different species live and interact in the same place, they form a microbial...

ecological niche

Microbial Niches in Ecosystems

Microbial niches describe how microorganisms survive, grow, and interact in an ecosystem. A niche includes how a microbe gets resources, reproduces, and relates to other species in its environment. This idea helps explain microbial community dynamics, biogeography, and ecosystem function. A microorganism’s fundamental niche is the full range of conditions where it could survive, grow, and reproduce. These conditions include both biotic factors, such as living interactions, and abiotic factors,...

methods to assess microbial populations

Measuring Microbes in Samples

Measuring microbes in a sample helps scientists study health, ecology, and industry. Microbial counts can show how many cells are present, how diverse they are, and what they may be doing. To do this, researchers use both culture-based and molecular methods. A viable plate count is a classic culture method for estimating living microbes. The sample is first diluted step by step, then spread on nutrient agar plates. Each viable cell can grow into a visible colony, so the colonies can be counted.

methods to assess microbial communities

Measuring Microbial Diversity and Activity

Microbial communities include bacteria, archaea, and eukaryotic microorganisms. They live in many ecosystems and affect important environmental and biological processes. Scientists study these communities by looking at how many species are present, how many individuals each species has, and how evenly the species are spread out. Species richness is the number of different species in a sample. Species abundance is the relative amount of each species. Species evenness describes how uniformly the...

the winogradsky column

Microbial Layers Inside a Winogradsky Column

A Winogradsky column shows how microbial layers form in a simple, sealed ecosystem. It is a clear model for studying microbial ecology and how different metabolisms interact in sediment over time. The setup uses a transparent glass cylinder. Half of it is filled with sediment mixed with cellulose, such as shredded paper, calcium carbonate, and gypsum. The cellulose provides a carbon source. Calcium carbonate buffers pH, and gypsum supplies sulfate. The rest of the cylinder is filled with pond...

microenvironments

Microbial Niches in Tiny Habitats

Microorganisms live in tiny habitats called microenvironments. These spaces have their own physical and chemical conditions. Oxygen level, pH, temperature, light, and nutrient supply can all differ from the surrounding area. These local conditions strongly affect microbial growth, metabolism, and which species can live there. Microenvironments often have sharp gradients over very small distances. In soil, oxygen may be available at the particle surface but drop off just a few millimeters below.

microbial mats

Microbial mats are layered communities of microbes that grow in response to changes in light, oxygen, and nutrients. These ecosystems are highly organized, and different microorganisms live at different depths. Biofilms are the early stage of this growth and are only a few millimeters thick. Mature microbial mats can grow to centimeter scale and show clear vertical structure. This layered arrangement lets microbes fill separate niches within a very small space. In cyanobacterial mats from hot...

microbial interactions: mutualism

Mutualistic Partnerships in Nature

Mutualistic partnerships in nature show how two or more organisms can benefit from living together. These symbiotic relationships can be obligate, meaning the partners depend on each other, or facultative, meaning the association is helpful but not required. Mutualism helps support many ecosystem functions across land and water. One common example is the partnership between plant roots and mycorrhizal fungi, such as Rhizophagus species. The fungal hyphae grow into the root hairs and epidermis,...

microbial interactions: cooperation

Microbial Cooperation in Soil and Hosts

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microbial interactions: predation

How Microbes Hunt and Defend

Microbial predation is a form of interaction in which one microorganism kills and eats another to gain nutrients and energy. It includes both bacterial predators and protozoan predators. This process helps shape microbial communities and affects how nutrients move through the environment. Some bacterial predators attack from the outside, while others enter the prey cell. Epibiotic predators, such as Vampirococcus, attach to the surface of a prey cell and release hydrolytic enzymes. These...

microbial interactions: competition

Microbial Competition and Niche Partitioning

Microbial competition shapes how bacteria and other microbes share space and resources. In shared environments, they compete for nutrients, space, or light. The strength of this competition depends on the environment, including nutrient levels, space limits, and how many microbial species are present. These interactions help determine the structure, function, and resilience of microbial communities. Microbial competition is usually grouped into exploitative competition and interference...

microbial interactions: parasitism

Microbial Parasites and Host Dependence

Microbial parasites depend on a host for nutrients and shelter, and this dependence often harms the host. In parasitism, only the parasite benefits. This is different from mutualism, where both organisms gain from the relationship. Microbial parasites are classified by where they live in or on the host. Ectoparasites stay on the host’s surface, such as the skin or outer tissues, and take in nutrients from outside. Endoparasites live inside the host’s body and invade tissues or organs.

microbe-plant interactions

How Plant Microbes Affect Growth

Plant microbes can help, harm, or simply live alongside their hosts. These microbe-plant interactions shape plant growth, health, and ecosystem function. The plant microbiome includes bacteria, fungi, archaea, protists, and viruses, and these organisms may live on the plant surface, inside plant tissues, or in symbiosis throughout the plant. Some of the most important beneficial partnerships involve mycorrhizal fungi. These fungi form close connections with roots and are grouped as arbuscular...

microbes and the carbon cycle

How Microbes Move Carbon Through Earth

Microbes move carbon through Earth’s major reservoirs and help drive the carbon cycle. Carbon shifts among the biosphere, lithosphere, atmosphere, and hydrosphere, where it supports life and helps regulate climate. It commonly cycles as carbon dioxide (CO2), the oxidized form of carbon, but methane (CH4) and organic compounds also matter. Photosynthetic microbes take in atmospheric CO2 and turn it into organic carbon. Cyanobacteria are especially important because they carry out oxygenic...

microbes and methanogenesis

How Microbes Produce Methane

Methane production in anaerobic ecosystems depends on methanogenic archaea and the microbes that work with them. This process happens where oxygen is absent, such as wetlands, sediments, and animal gastrointestinal tracts. In these anoxic habitats, aerobic respiration cannot run, so microbes use other pathways to break down organic matter. Anaerobic decomposition starts when cellulolytic bacteria, or cellulose-digesting bacteria, hydrolyze dead organic material into simple sugars. Other...

microbes and the nitrogen cycle

Microbial Steps in the Nitrogen Cycle

Microbes drive the nitrogen cycle by changing nitrogen into forms that plants and other organisms can use. This biogeochemical cycle keeps nitrogenous compounds balanced in ecosystems. It also supports plant growth and microbial growth. Nitrogen fixation begins the cycle by converting inert atmospheric nitrogen gas, N2, into ammonia, NH3. This step depends on nitrogenase enzymes. Free-living diazotrophs do this on their own. Aerobic bacteria such as Azotobacter spp. and anaerobic bacteria such...

microbes and the sulfur cycle

Sulfur Cycling Through Microbial Reactions

Sulfur cycling depends on microbial reactions that move sulfur through rocks, water, soil, and the air. In Earth systems, sulfur shifts among inorganic forms such as sulfate, elemental sulfur, and sulfide. These changes happen through both abiotic processes and biological activity in oxic and anoxic environments. Sulfate is the most oxidized form of sulfur. It is stored mainly in rocks, marine sediments, and ocean water, where it acts as a long-term reservoir in the global sulfur cycle. In...

microbes and other elemental cycles

Microbes Driving Iron and Manganese Cycles

Microbes drive iron and manganese cycling in aquatic environments by changing these metals between reduced and oxidized forms. These reactions are especially important along redox gradients, where oxygen levels shift across stratified water layers. The microbes use these metals for energy, growth, and structural needs. In oxygen-rich surface waters, iron is usually present as insoluble ferric iron, Fe(III). Some bacteria release siderophores, which are small organic molecules that bind ferric...

marine microbial ecology

Microbial Life in the Ocean

Marine microbial life is shaped by salinity, low nutrients, and changing oxygen levels. These physical and chemical limits influence which microbes can survive and how they function. They also affect how ocean microbes help drive nutrient and carbon cycling. Small cell size is common in these environments because it gives microbes a larger surface-to-volume ratio. That helps them take up nutrients more efficiently when nutrients are scarce. In estuaries, where salinity changes often,...

deep sea microbial ecology

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...

freshwater microbial ecology

Microbes in Streams, Lakes, and Rivers

Freshwater microbes live in streams, rivers, lakes, ponds, and marshes, but their communities change with water movement, light, depth, and nutrients. These systems are often grouped into lotic waters, which flow, and lentic waters, which are still or slow-moving. The physical setting shapes where microbes grow and how they get energy. In lentic systems, phytoplankton are the main producers. They make autochthonous organic carbon, which means carbon made within the water body. In lotic...

soil microbial ecology

How Soil Microbes Cycle Nutrients

Soil microbes drive nutrient cycling, organic matter turnover, and ecosystem stability. A gram of soil can contain thousands of bacterial and archaeal taxa, but their shared job is what helps sustain land ecosystems. Their activity changes the way carbon, nitrogen, and other nutrients move through soil. Soil is a patchwork of minerals, organic matter, water, and air. Microbes live in tiny microhabitats shaped by pore size, moisture, oxygen, and nutrients. Sandy soils drain fast and tend to...

key terms and concepts

Learn how microbial mats form layered communities, from oxygen-making cyanobacteria at the surface to sulfate reducers and Thioploca in deeper zones.

Microbial Mats and Oxygen Gradients | 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

Microbial Mats and Oxygen Gradients

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