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

Stickstoff ist ein Hauptbestandteil von Proteinen, Nukleinsäuren, Coenzymen und anderen Zellbestandteilen. Die meisten Bakterien und Archaeen assimilieren Stickstoff in Form von Nitrat und Ammoniak. Nitrat gelangt in die Zellen und wird nacheinander durch Nitratreduktase zu Nitrit und dann durch Nitritreduktase zu Ammoniak reduziert, in einem Prozess, der als assimilatorische Nitratreduktion bezeichnet wird. Die Ammoniakassimilation erfolgt über zwei Hauptwege, abhängig vom Ammoniakgehalt. Bei hohen Ammoniakgehalten nutzen Bakterien und Pilze den reduktiven Aminierungsweg, bei dem Glutamatdehydrogenase α-Ketoglutarat in Glutamat umwandelt. Bei niedrigen Ammoniakgehalten wird das Glutamin-Synthetase-Glutamat-Synthase-System oder GS-GOGAT-System aktiviert. Hier wandelt die Glutaminsynthetase (GS) Ammoniak und Glutamat in Glutamin um, das dann von der Glutamatsynthase (GOGAT) verarbeitet wird, um zwei Glutamatmoleküle zu produzieren. Die Stickstoffassimilation unterscheidet sich von der Stickstofffixierung, einem Prozess, der nur bei bestimmten Prokaryoten vorkommt. Bei der Stickstofffixierung wandeln Nitrogenase-Enzyme Luftstickstoff in Ammoniak um und machen ihn biologisch verfügbar.

anorganische stickstoffassimilation

Inorganic Nitrogen Assimilation

Stickstoff ist ein essentielles Element in biologischen Systemen und bildet einen entscheidenden Bestandteil von Proteinen, Nukleins&#228;uren und anderen zellul&#228;ren Bestandteilen. Viele Bakterien und Archaeen nehmen Stickstoff in Form von Nitrat (NO_3^-) oder Ammoniak (NH_3) auf und bauen ihn anschlie&#223;end &#252;ber spezifische enzymatische Stoffwechselwege in Biomolek&#252;le ein.
Assimilatorische Nitratreduktion
Wenn Nitrat in die Zelle gelangt, durchl&#228;uft es einen zweistufigen Reduktionsprozess, der als assimilatorische Nitratreduktion bezeichnet wird. Zun&#228;chst katalysiert das Enzym Nitratreduktase die Reduktion von Nitrat zu Nitrit (NO_2^-), wobei abh&#228;ngig von den Umwelt- und Zellbedingungen, NADH oder FAD, als Elektronendonor dienen. Im Anschluss daran wandelt die Nitritreduktase, die meist Ferredoxin als Kofaktor ben&#246;tigt, Nitrit in Ammoniak um, welcher direkt in zellul&#228;re Komponenten eingebaut werden kann. Der Prozess verl&#228;uft wie folgt:
<ul>
<li>Nitrataufnahme &#8211; Nitrat wird &#252;ber spezifische Membrantransporter in die Zelle transportiert.</li>
<li>Nitratreduktion &#8211; Die Nitratreduktase reduziert NO_3^- zu NO_2^- unter Verwendung von Elektronen aus NADH oder FAD.</li>
<li>Nitritreduktion &#8211; Die Nitritreduktase reduziert NO_2^- mit Ferredoxin als Kofaktor weiter zu NH_3 und macht Stickstoff so f&#252;r den Zellstoffwechsel verf&#252;gbar.</li>
</ul>
Im Gegensatz zur Denitrifikation, welche bioverf&#252;gbaren Stickstoff aus &#214;kosystemen entfernt und durch die Umwandlung von Nitraten in gasf&#246;rmige Formen eine wichtige Rolle im Stickstoffkreislauf spielt, dient die assimilatorische Nitratreduktion dem Einbau von Stickstoff in organische Molek&#252;le und gew&#228;hrleistet dessen Verbleib in der Zelle. Dieser Prozess ist eng mit dem Zellstoffwechsel verbunden, da Ammoniak zur weiteren Assimilation bereitgestellt wird.
Assimilation von Ammoniak
Ammoniak, das entweder direkt aufgenommen oder durch Nitratreduktion erzeugt wird, muss in organische Molek&#252;le eingebaut werden, um im Zellstoffwechsel verwendet werden zu k&#246;nnen. Abh&#228;ngig von der Verf&#252;gbarkeit von Ammoniak in der Umwelt erfolgt die Assimilation &#252;ber zwei Hauptwege.
Reduktive Aminierung
Bei hohen Ammoniakkonzentrationen bevorzugen Bakterien und Pilze den Weg der reduktiven Aminierung. Dabei laufen folgende Schritte ab:
<ul>
<li>Bildung von &#945;-Ketoglutarat &#8211; &#945;-Ketoglutarat, ein zentrales Zwischenprodukt des Tricarbons&#228;urezyklus, wird synthetisiert.</li>
<li>Synthese von Glutamat &#8211; Das Enzym Glutamatdehydrogenase (GDH) katalysiert die Umwandlung von &#945;-Ketoglutarat zu Glutamat unter Einbau von Ammoniak und unter Verwendung von NAD(P)H als Reduktionsmittel.</li>
</ul>
Dieser Weg erm&#246;glicht eine schnelle Einbindung von Ammoniak bei Stickstoff&#252;berschuss.
Glutamin-Synthetase&#8211;Glutamat-Synthase-System (GS-GOGAT-System)
Bei geringer Ammoniakverf&#252;gbarkeit nutzen Mikroorganismen das GS-GOGAT-System, das zwar energieaufwendiger, jedoch besonders effizient f&#252;r die Stickstoffassimilation ist. Der Ablauf ist wie folgt:
<ul>
<li>Bildung von Glutamin &#8211; Glutaminsynthetase (GS) katalysiert die Reaktion zwischen Ammoniak und Glutamat unter ATP-Verbrauch zu Glutamin.</li>
<li>Synthese von Glutamat &#8211; Glutamatsynthase (GOGAT) wandelt Glutamin mithilfe von NADPH als Reduktionsmittel in zwei Molek&#252;le Glutamat um.</li>
<li>Stickstoffverteilung &#8211; Das gebildete Glutamat dient als Stickstoffdonor f&#252;r biosynthetische Wege und stellt sicher, dass Stickstoff effizient assimiliert und in Stoffwechselprozesse wie die Synthese von Aminos&#228;uren und Nukleotiden eingebunden wird.</li>
</ul>
Stickstofffixierung und ihre Rolle im Stickstoffkreislauf
Im Gegensatz zur Stickstoffassimilation ist die Stickstofffixierung ein eigenst&#228;ndiger Prozess, der ausschlie&#223;lich bei bestimmten Prokaryoten wie diazotrophen Bakterien und Archaeen vorkommt. Dabei wird molekularer Stickstoff (N_2) durch den Enzymkomplex Nitrogenase enzymatisch in bioverf&#252;gbares Ammoniak reduziert. Die Aktivit&#228;t der Nitrogenase erfordert ATP und Elektronen, was diesen Prozess besonders energieaufwendig macht. Die Stickstofffixierung spielt eine zentrale Rolle im globalen Stickstoffkreislauf, da sie die Reserven von biologisch nutzbarem Stickstoff in stickstoffarmen &#214;kosystemen wieder auff&#252;llt.
Zusammenfassung
Die Stickstoffassimilation &#252;ber die Nitratreduktion und der Einbau von Ammoniak ist grundlegend f&#252;r das &#220;berleben von Mikroorganismen und f&#252;r das Funktionieren von &#214;kosystemen. Durch die Integration dieser Prozesse in zentrale Stoffwechselwege wie den Citratzyklus und die Aminos&#228;urebiosynthese wird gew&#228;hrleistet, dass Stickstoff effizient in den Zellstoffwechsel eingebaut wird. Diese Vorg&#228;nge unterst&#252;tzen das mikrobielle Wachstum und tragen wesentlich zur Aufrechterhaltung des globalen Stickstoffhaushalts bei.

Anorganische Stickstoffassimilation

Stickstoff ist ein essentielles Element in biologischen Systemen und bildet einen entscheidenden Bestandteil von Proteinen, Nukleins&#228;uren und anderen ...

Education

Lehre

JoVE Core

Microbiology

Mikrobiologie

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Einheit

Microbial Metabolism

Mikrobieller Stoffwechsel

KEY TERMS AND CONCEPTS

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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

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atp and energy production

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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...

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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...

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Glucose Breakdown and ATP Production

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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

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cellular respiration

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electron transport chain components

Electron Transport Chain and ATP Production

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Electron Transport Chain Powers ATP Output

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respiration pathways

TCA Cycle and Energy Pathways

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microbial fermentation

Fermentation Products in Microbes

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metabolism of chemolithotrophs

How Chemolithotrophs Make ATP

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amino acid catabolism

Microbes Use Proteins for Energy

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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

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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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