Name: nitrogen uptake by microbes
Uploaded: 2025-06-12T09:37:36.000Z
Duration: 1 min 22 s
Channel: JoVE

L’azote est un composant majeur des protéines, des acides nucléiques, des coenzymes et d’autres constituants cellulaires. La plupart des bactéries et des archées assimilent l’azote sous forme de nitrate et d’ammoniac. Le nitrate pénètre dans les cellules et est réduit séquentiellement en nitrite par la nitrate réductase, puis en ammoniac par la nitrite réductase, dans un processus appelé réduction assimilatrice du nitrate. L’assimilation de l’ammoniac se fait par deux voies principales, en fonction des niveaux d’ammoniac. À des niveaux élevés d’ammoniac, les bactéries et les champignons utilisent la voie d’amination réductrice, où la glutamate déshydrogénase convertit le α-cétoglutarate en glutamate. À de faibles niveaux d’ammoniac, le système glutamine synthétase-glutamate synthase ou GS-GOGAT est activé. Ici, la glutamine synthétase, ou GS, convertit l’ammoniac et le glutamate en glutamine, qui est ensuite traitée par la glutamate synthase, ou GOGAT, pour produire deux molécules de glutamate. L’assimilation de l’azote diffère de la fixation de l’azote, un processus unique à certains procaryotes. Dans la fixation de l’azote, les enzymes nitrogénases convertissent l’azote atmosphérique en ammoniac, ce qui le rend biologiquement disponible.

assimilation de l’azote inorganique

Inorganic Nitrogen Assimilation

L&#8217;azote est un &#233;l&#233;ment essentiel des syst&#232;mes biologiques, constituant une composante fondamentale des prot&#233;ines, des acides nucl&#233;iques et d&#8217;autres &#233;l&#233;ments cellulaires. De nombreuses bact&#233;ries et arch&#233;es acqui&#232;rent l&#8217;azote sous forme de nitrate (NO_3^-) ou d&#8217;ammoniac (NH_3), qui sont ensuite assimil&#233;s dans les biomol&#233;cules par le biais de voies enzymatiques sp&#233;cifiques.
R&#233;duction assimilatrice du nitrate
Lorsque le nitrate p&#233;n&#232;tre dans la cellule, il subit un processus de r&#233;duction en deux &#233;tapes connu sous le nom de r&#233;duction assimilatrice du nitrate. Dans un premier temps, l&#8217;enzyme nitrate r&#233;ductase catalyse la r&#233;duction du nitrate en nitrite (NO_2^-), en utilisant le NADH ou le FAD comme donneur d&#8217;&#233;lectrons, selon les conditions environnementales et cellulaires. Ensuite, la nitrite r&#233;ductase, n&#233;cessitant souvent la ferredoxine comme cofacteur, convertit le nitrite en ammoniac, qui peut &#234;tre directement assimil&#233; dans les composants cellulaires. Ce processus comprend les &#233;tapes suivantes :
<ul>
<li>Absorption du nitrate &#8211; Le nitrate est transport&#233; dans la cellule via des transporteurs membranaires sp&#233;cifiques.</li>
<li>R&#233;duction du nitrate &#8211; La nitrate r&#233;ductase r&#233;duit NO_3^- en NO_2^- &#224; l&#8217;aide d&#8217;&#233;lectrons provenant du NADH ou du FAD.</li>
<li>R&#233;duction du nitrite &#8211; La nitrite r&#233;ductase, avec la ferredoxine comme cofacteur, r&#233;duit NO_2^- en NH_3, rendant l&#8217;azote disponible pour le m&#233;tabolisme cellulaire.</li>
</ul>
Contrairement &#224; la d&#233;nitrification, qui &#233;limine l&#8217;azote biodisponible des &#233;cosyst&#232;mes en le convertissant en formes gazeuses et joue un r&#244;le crucial dans l&#8217;&#233;quilibre global de l&#8217;azote, la r&#233;duction assimilatrice du nitrate vise &#224; incorporer l&#8217;azote dans les mol&#233;cules organiques, assurant sa r&#233;tention au sein de la cellule. Ce processus s&#8217;int&#232;gre au m&#233;tabolisme cellulaire en fournissant l&#8217;ammoniac n&#233;cessaire &#224; l&#8217;assimilation.
Voies d&#8217;assimilation de l&#8217;ammoniac
L&#8217;ammoniac, qu&#8217;il soit acquis par absorption directe ou g&#233;n&#233;r&#233; par r&#233;duction du nitrate, doit &#234;tre incorpor&#233; dans des mol&#233;cules organiques pour participer au m&#233;tabolisme cellulaire. Selon la disponibilit&#233; environnementale en ammoniac, son assimilation se fait par deux voies principales.
Voie de l&#8217;amination r&#233;ductrice
Lorsque les concentrations d&#8217;ammoniac sont &#233;lev&#233;es, les bact&#233;ries et les champignons utilisent pr&#233;f&#233;rentiellement la voie de l&#8217;amination r&#233;ductrice. Ce processus se d&#233;roule ainsi :
<ul>
<li>Formation de l&#8217;&#945;-c&#233;toglutarate &#8211; L&#8217;&#945;-c&#233;toglutarate, un interm&#233;diaire cl&#233; du cycle de l&#8217;acide tricarboxylique (TCA), est synth&#233;tis&#233;.</li>
<li>Synth&#232;se du glutamate &#8211; L&#8217;enzyme glutamate d&#233;shydrog&#233;nase (GDH) catalyse la conversion de l&#8217;&#945;-c&#233;toglutarate en glutamate en incorporant de l&#8217;ammoniac et en utilisant le NAD(P)H comme agent r&#233;ducteur.</li>
</ul>
Cette voie permet une incorporation rapide de l&#8217;ammoniac lorsque l&#8217;azote est abondant.
Syst&#232;me glutamine synth&#233;tase&#8211;glutamate synthase (GS-GOGAT)
En conditions de faible disponibilit&#233; en ammoniac, les micro-organismes utilisent la voie GS-GOGAT, plus co&#251;teuse en &#233;nergie mais tr&#232;s efficace pour l&#8217;assimilation de l&#8217;azote. Ce syst&#232;me suit les &#233;tapes suivantes :
<ul>
<li>Formation de la glutamine &#8211; La glutamine synth&#233;tase (GS) catalyse la r&#233;action entre l&#8217;ammoniac et le glutamate pour former la glutamine dans une r&#233;action d&#233;pendante de l&#8217;ATP.</li>
<li>Synth&#232;se du glutamate &#8211; La glutamate synthase (GOGAT) convertit la glutamine en deux mol&#233;cules de glutamate, en utilisant le NADPH comme agent r&#233;ducteur.</li>
<li>Redistribution de l&#8217;azote &#8211; Le glutamate form&#233; sert de donneur d&#8217;azote dans les voies biosynth&#233;tiques, garantissant une assimilation et une utilisation efficaces de l&#8217;azote dans les processus m&#233;taboliques, notamment la synth&#232;se des acides amin&#233;s et des nucl&#233;otides.</li>
</ul>
Fixation de l&#8217;azote et son r&#244;le dans le cycle de l&#8217;azote
Contrairement &#224; l&#8217;assimilation de l&#8217;azote, la fixation de l&#8217;azote est un processus distinct, observ&#233; exclusivement chez certains procaryotes, comme les bact&#233;ries diazotrophes et certaines arch&#233;es. Ce processus implique la r&#233;duction enzymatique de l&#8217;azote atmosph&#233;rique (N_2) en ammoniac biodisponible &#224; l&#8217;aide du complexe enzymatique nitrog&#233;nase. L&#8217;activit&#233; de la nitrog&#233;nase requiert de l&#8217;ATP et des &#233;lectrons, ce qui en fait un processus &#233;nerg&#233;tiquement co&#251;teux. La fixation de l&#8217;azote joue un r&#244;le essentiel dans le cycle global de l&#8217;azote en r&#233;approvisionnant les &#233;cosyst&#232;mes en azote utilisable, en particulier dans les environnements pauvres en azote.
Conclusion
L&#8217;assimilation de l&#8217;azote par r&#233;duction du nitrate et incorporation de l&#8217;ammoniac est fondamentale pour la survie microbienne et le fonctionnement des &#233;cosyst&#232;mes. L&#8217;int&#233;gration de ces voies aux r&#233;seaux m&#233;taboliques centraux, tels que le cycle TCA et la biosynth&#232;se des acides amin&#233;s, garantit une incorporation efficace de l&#8217;azote dans le m&#233;tabolisme cellulaire. Ces processus soutiennent collectivement la croissance microbienne et contribuent &#224; l&#8217;&#233;quilibre global de l&#8217;azote.

Assimilation de l’azote inorganique

L&#8217;azote est un &#233;l&#233;ment essentiel des syst&#232;mes biologiques, constituant une composante fondamentale des prot&#233;ines, des acides ...

Education

Enseignement

JoVE Core

Microbiology

Microbiologie

Unit

Unité

Microbial Metabolism

Métabolisme microbien

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

nitrogen uptake by microbes

Nitrogen uptake by microbes is essential for making proteins, nucleic acids, and other cell parts. Many bacteria and archaea take in nitrogen as nitrate or ammonia. They then convert it into forms that can be built into biomolecules.

When nitrate enters a cell, it goes through assimilatory nitrate reduction. This is a two-step process. First, nitrate reductase changes nitrate to nitrite using NADH or FAD as an electron donor, depending on environmental and cellular conditions. Then nitrite reductase, often with ferredoxin as a cofactor, reduces nitrite to ammonia.

The ammonia made from nitrate can be used directly in cellular metabolism. Nitrate must first move into the cell through specific membrane transporters. This pathway is different from denitrification. Denitrification removes bioavailable nitrogen from ecosystems by converting nitrates to gaseous forms. In contrast, assimilatory nitrate reduction keeps nitrogen inside the cell in organic form.

Ammonia can also enter cells directly, but it still must be built into organic molecules. Microbes use two main ammonia assimilation pathways. When ammonia levels are high, bacteria and fungi often use reductive amination. In this pathway, alpha-ketoglutarate, a TCA cycle intermediate, is formed and glutamate dehydrogenase uses ammonia and NAD(P)H to make glutamate.

When ammonia is scarce, microbes use the GS-GOGAT system. This pathway uses more energy but is very efficient. Glutamine synthetase first combines ammonia and glutamate to form glutamine in an ATP-dependent reaction. Then glutamate synthase uses NADPH to turn glutamine into two molecules of glutamate. The glutamate produced helps supply nitrogen for amino acid and nucleotide synthesis.

Nitrogen fixation is related to, but different from, nitrogen assimilation. It occurs only in some prokaryotes, such as diazotrophic bacteria and archaea. In this process, the nitrogenase enzyme complex reduces atmospheric nitrogen gas to ammonia. Because it needs ATP and electrons, nitrogen fixation is energy-intensive. It helps replenish usable nitrogen in nitrogen-poor environments and supports the global nitrogen cycle.

Together, nitrate reduction, ammonia assimilation, and nitrogen fixation help microbes survive and grow. These pathways connect nitrogen use with core metabolism, including the TCA cycle and biosynthesis of amino acids. They also help maintain the balance of nitrogen in ecosystems.

Nitrogen Uptake by Microbes

microbial nutrition

Microbial Energy and Carbon Sources

Microbial energy and carbon sources determine how microorganisms live and grow. These metabolic strategies help microbes survive in many habitats and keep energy moving through ecosystems. They also support nutrient cycling in nature. Microbes are grouped by where they get energy, electrons, and carbon. Phototrophs use light, while chemotrophs use chemical compounds for energy. Lithotrophs take electrons from reduced inorganic substances, and organotrophs take them from organic compounds.

atp and energy production

How Cells Make and Use ATP

ATP is the main energy carrier in cells. It is made of adenosine, which includes adenine and ribose, plus three phosphate groups. The bonds between the phosphate groups hold a large amount of potential energy. When ATP is hydrolyzed, it becomes ADP or AMP and releases energy for cell work. Cells use that energy for many essential tasks. It supports macromolecule synthesis, intracellular transport, and mechanical movement. ATP also acts as an energy manager by linking catabolic and anabolic...

redox reactions

Electron Carriers in Redox Metabolism

Redox reactions move electrons through metabolic pathways in cells. Oxidation is the loss of electrons, and reduction is the gain of electrons. These two steps happen together, which keeps electron flow moving through metabolism. A clear example appears in bacterial metabolism. Glucose is oxidized to carbon dioxide, while oxygen is reduced to water. This shows how one molecule loses electrons as another gains them. Cells use special electron carriers to make these transfers happen.

introduction to metabolism

Metabolism: Energy Use and Biomolecule Synthesis

Metabolism is the set of chemical reactions that keep living cells working. It includes reactions that break down biomolecules and reactions that build them up. These two sides of metabolism work together to support energy balance and cell function. Catabolic pathways break large molecules into smaller parts. Carbohydrates, lipids, and proteins can be broken down into monosaccharides, fatty acids, and amino acids. These reactions release energy, and cells store much of that energy as ATP, or...

carbohydrate catabolism

Glucose Breakdown and ATP Production

Glucose breakdown is a key part of cell metabolism that lets cells make ATP, the usable form of energy. The process follows two main paths: cellular respiration and fermentation. Both start with glycolysis, which does not require oxygen. Glycolysis splits one glucose molecule into two molecules of pyruvic acid. It also produces a net gain of two ATP molecules and two NADH molecules. This step sets up the cell to continue with respiration or switch to fermentation, depending on whether oxygen...

glycolysis

Glycolysis and Pyruvate Fate

Glycolysis is a central pathway in glucose catabolism and a major way cells make energy. It is also called the Embden-Meyerhof pathway. This process takes place in the cytoplasm and can work with or without oxygen, which makes it useful in many organisms and conditions. Glycolysis has ten steps and turns one glucose molecule into two pyruvate molecules. It has two phases. In the preparatory phase, the cell uses two ATP to add phosphate groups to glucose and split it into two three-carbon...

other glycolytic pathways

Pentose Phosphate Pathway and Entner-Doudoroff

The pentose phosphate pathway works alongside glycolysis in cells that need both sugar breakdown and building blocks for growth. It handles pentoses, which are five-carbon sugars, and also uses glucose as a starting point. The pathway has two parts, an oxidative phase and a non-oxidative phase. It does not make ATP directly, but its products can feed back into glycolysis when the cell needs them. The oxidative phase mainly makes NADPH, a reduced electron carrier. In this phase,...

cellular respiration

Cellular Respiration: ATP Production Pathways

Cellular respiration is the process cells use to turn glucose into ATP, the main energy molecule in the cell. It depends on oxidation and the transfer of electrons to a separate electron acceptor. This sequence of reactions supports energy production in both aerobic and anaerobic settings. Glycolysis is the first step. It takes place in the cytoplasm of both prokaryotic and eukaryotic cells. One glucose molecule is broken into two pyruvate molecules, and the cell gains a net 2 ATP and 2 NADH.

electron transport chain components

Electron Transport Chain and ATP Production

The electron transport chain helps cells make ATP by moving electrons through membrane protein complexes. In eukaryotic cells, it sits in the inner mitochondrial membrane. In prokaryotic cells, it is found in the plasma membrane and can differ in the number and type of complexes, depending on the organism and its environment. The chain uses several electron carriers to pass electrons along in redox reactions, which are reactions that involve oxidation and reduction. These carriers include...

chemiosmosis and atp synthesis

Electron Transport Chain Powers ATP Output

The electron transport chain powers ATP production during cellular respiration. It sits in the inner mitochondrial membrane and moves high-energy electrons from NADH and FADH2 to molecular oxygen, the final electron acceptor. As electrons move through the chain, protons are pushed across the membrane to build the gradient needed for ATP synthesis. Electrons from NADH enter the chain at Complex I, also called NADH: ubiquinone oxidoreductase. In prokaryotes, this step helps pump protons from the...

respiration pathways

TCA Cycle and Energy Pathways

Cellular respiration uses the TCA cycle, also called the Krebs cycle, to help cells make usable energy from organic molecules. This pathway is a central part of aerobic respiration and also supports biosynthesis. It links the breakdown of food molecules to the cell's energy needs. Pyruvate from glycolysis enters this process first. The pyruvate dehydrogenase complex converts pyruvate into acetyl-CoA through oxidative decarboxylation. This step produces one NADH and one carbon dioxide molecule.

microbial fermentation

Fermentation Products in Microbes

Fermentation is an anaerobic process that lets microbes make energy from sugar without oxygen or an electron transport chain. It is important in both biology and industry. The process is grouped by the products it makes. Pyruvate and its derivatives act as key electron acceptors in fermentative pathways. This step helps oxidize NADH back to NAD+, which is needed for glycolysis to keep running. Without NAD+ regeneration, glycolysis would stop and the cell would lose its main source of ATP under...

metabolism of chemolithotrophs

How Chemolithotrophs Make ATP

Chemolithotrophs make ATP by using inorganic chemicals as an energy source. They oxidize molecules such as hydrogen gas, ammonia, reduced sulfur compounds, and ferrous iron. Instead of relying on organic carbon like heterotrophs, they move electrons from these inorganic donors into the electron transport chain, or ETC. That electron flow builds a proton motive force, or PMF. The PMF drives ATP synthesis through oxidative phosphorylation. Because inorganic electron donors usually release less...

amino acid catabolism

Microbes Use Proteins for Energy

Microbes can use proteins as a carbon and energy source, especially when polysaccharides or lipids are scarce. But proteins are too large to pass through the plasma membrane on their own. To solve this, microbes secrete extracellular proteases and peptidases that break proteins into peptides. The peptides are then transported into the cell, where intracellular proteases cut them into free amino acids. Once amino acids are available, microbes break them down in two main ways: deamination and...

lipid catabolism

How Microbes Break Down Fats for Energy

Microbes break down triglycerides and fatty acids to make energy. Triglycerides are important long-term energy storage molecules in microorganisms. Lipases hydrolyze, or split with water, triglycerides into glycerol and free fatty acids. Each product then enters a different metabolic route that helps the cell make ATP, the main energy currency. Glycerol metabolism begins after glycerol is released from triglyceride hydrolysis. Glycerol kinase adds a phosphate group to form glycerol-3-phosphate.

oxygenic photosynthesis

How Plants Make Oxygen and ATP

Oxygenic photosynthesis is the process plants, algae, and cyanobacteria use to capture light energy and turn it into chemical energy. It uses water as the source of electrons and releases molecular oxygen, or O2. The process also produces ATP and NADPH, which cells need for later energy use and carbon fixation. The main reactions happen in the thylakoid membranes, where chlorophyll pigments absorb light. In cyanobacteria, these membranes come from folds in the plasma membrane. Two photosystems...

anoxygenic photosynthesis

Bacterial Light Capture Without Oxygen

Anoxygenic photosynthesis is a bacterial way to capture light energy without making oxygen. It supports carbon fixation, but it does not use water as the electron donor. Instead, these phototrophs use other electron donors such as hydrogen sulfide, elemental sulfur, thiosulfate, or organic compounds. This process is carried out by several groups of bacteria, including purple bacteria, green sulfur bacteria, heliobacteria, and other anoxygenic phototrophs. These organisms have evolved a...

biosynthesis in bacteria

How Bacteria Build Key Macromolecules

Bacteria build essential macromolecules through tightly controlled biosynthetic pathways. These anabolic reactions make proteins, nucleic acids, lipids, and polysaccharides. The products support growth, cell division, and normal cell function. Bacterial biosynthesis starts with precursor metabolites from glycolysis, the pentose phosphate pathway, and the Krebs cycle. Important precursors include pyruvate, acetyl-CoA, and glucose-6-phosphate. Cells use these compounds to make the monomers that...

carbon-dioxide fixation

Microbial Carbon Fixation Pathways

Microbial carbon fixation pathways let prokaryotes turn carbon dioxide into organic molecules. This process supports biosynthesis, helps sustain ecosystems, and plays a role in the global carbon cycle. It also has industrial uses in carbon capture and bioproduct synthesis. Autotrophic organisms depend on this process to use CO2 as a carbon source in many environments. The Calvin cycle is the most common carbon fixation pathway. Cyanobacteria and other autotrophic prokaryotes use it, and it...

biosynthesis of polysaccharides

Activated Sugars for Polysaccharide Synthesis

Activated sugars drive polysaccharide synthesis in cells. Glycogen and starch are built from nucleoside diphosphate sugars, mainly uridine diphosphate glucose (UDPG) and adenosine diphosphate glucose (ADPG). These sugar donors act as high-energy intermediates in carbohydrate metabolism and biosynthesis. UDPG supports glycogen synthesis in animals and many bacteria. It forms when glucose-1-phosphate reacts with uridine triphosphate (UTP). UDP-glucose pyrophosphorylase catalyzes this reaction.

inorganic nitrogen assimilation

Nitrogen uptake by microbes is essential for making proteins, nucleic acids, and other cell parts. Many bacteria and archaea take in nitrogen as nitrate or ammonia. They then convert it into forms that can be built into biomolecules. When nitrate enters a cell, it goes through assimilatory nitrate reduction. This is a two-step process. First, nitrate reductase changes nitrate to nitrite using NADH or FAD as an electron donor, depending on environmental and cellular conditions. Then nitrite...

sulfur assimilation

Sulfur Uptake and Cysteine Synthesis

Sulfur uptake and cysteine synthesis are key parts of microbial metabolism. Sulfur is needed to build important biomolecules, including the amino acids cysteine and methionine, as well as cofactors such as coenzyme A and biotin. Microorganisms usually take in sulfur from the environment as sulfate, but sulfate must be changed before cells can use it. Because sulfate is highly oxidized, it must go through assimilatory sulfate reduction to become biologically useful. Some microorganisms can also...

amino acid biosynthetic pathways

Amino Acid Building from Cell Metabolites

Amino acid biosynthesis lets cells build amino acids from common metabolic intermediates. These amino acids support cell growth, protein synthesis, and metabolic regulation. The main source molecules come from glycolysis, the tricarboxylic acid (TCA) cycle, and the pentose phosphate pathway. Key precursors include alpha-ketoglutarate, pyruvate, oxaloacetate, phosphoenolpyruvate, and erythrose-4-phosphate. They supply the carbon skeletons needed to form amino acids. Nitrogen must also be added...

biosynthesis of nucleic acids

Nucleotide Building Blocks for DNA and RNA

Nucleotide biosynthesis makes the building blocks needed for DNA and RNA. Cells use this pathway to make purine and pyrimidine nucleotides and keep their supply balanced. That balance helps protect genetic integrity and supports normal cell function. Purine nucleotide synthesis starts with ribose-5-phosphate, a sugar made in the pentose phosphate pathway. PRPP synthetase adds phosphate groups to form phosphoribosyl pyrophosphate, or PRPP, which is the activated starting point for the pathway.

biosynthesis of lipids

How Membrane Lipids Vary Across Life

Membrane lipids vary across Bacteria, Archaea, and Eukarya, and these differences help cells survive in different environments. The three domains of life make lipids through distinct biosynthetic pathways. Those pathways create membranes with different stability, permeability, and flexibility. Bacteria and eukaryotes both build fatty acid-based lipids from acetyl-CoA and malonyl-CoA. The pathway includes condensation, reduction, and dehydration steps. Bacteria use a type II fatty acid...

formation of lipopolysaccharides

Lipopolysaccharides and Gram-Negative Defense

Lipopolysaccharides (LPS) are important parts of the outer membrane of Gram-negative bacteria. They help stabilize the membrane and help protect bacteria from host immune responses. LPS has three main parts: lipid A, a core oligosaccharide, and an O antigen. LPS biosynthesis and assembly depend on a coordinated set of enzymes and transport steps. The molecule is also known as an endotoxin. It can activate Toll-like receptor 4 (TLR4) in the host and trigger strong immune responses. In severe...

key terms and concepts

Learn how bacteria and archaea take up nitrate or ammonia and convert them into cell material through nitrate reduction, GS-GOGAT, and nitrogen fixation.

Nitrogen Uptake by Microbes | 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

Nitrogen Uptake by Microbes

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