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

El nitrógeno es un componente principal de las proteínas, los ácidos nucleicos, las coenzimas y otros constituyentes celulares. La mayoría de las bacterias y arqueas asimilan el nitrógeno en forma de nitrato y amoníaco. El nitrato entra en las células y se reduce secuencialmente a nitrito por la nitrato reductasa, y luego a amoníaco por la nitrito reductasa, en un proceso llamado reducción asimiladora de nitratos. La asimilación del amoníaco se produce a través de dos vías principales, dependiendo de los niveles de amoníaco. A altos niveles de amoníaco, las bacterias y los hongos utilizan la vía de aminación reductora, donde la glutamato deshidrogenasa convierte el α-cetoglutarato en glutamato. A niveles bajos de amoníaco, se activa el sistema glutamina sintetasa-glutamato sintasa o GS-GOGAT. Aquí, la glutamina sintetasa, o GS, convierte el amoníaco y el glutamato en glutamina, que luego es procesada por la glutamato sintasa, o GOGAT, para producir dos moléculas de glutamato. La asimilación de nitrógeno difiere de la fijación de nitrógeno, un proceso exclusivo de ciertos procariotas. En la fijación de nitrógeno, las enzimas nitrogenasas convierten el nitrógeno atmosférico en amoníaco, lo que lo hace biológicamente disponible.

asimilación de nitrógeno inorgánico

Inorganic Nitrogen Assimilation

El nitr&#243;geno es un elemento esencial en los sistemas biol&#243;gicos, constituyendo un componente fundamental de las prote&#237;nas, los &#225;cidos nucleicos y otros constituyentes celulares. Muchas bacterias y arqueas adquieren nitr&#243;geno en forma de nitrato (NO_3^-) o amon&#237;aco (NH_3), que posteriormente se asimilan en biomol&#233;culas mediante rutas enzim&#225;ticas espec&#237;ficas.
Reducci&#243;n asimilatoria de nitrato
Cuando el nitrato entra en la c&#233;lula, se somete a un proceso de reducci&#243;n en dos etapas conocido como reducci&#243;n asimilatoria de nitrato. Inicialmente, la enzima nitrato reductasa cataliza la reducci&#243;n de nitrato a nitrito (NO_2^-), utilizando NADH o FAD, seg&#250;n las condiciones ambientales y celulares, como donadores de electrones. A continuaci&#243;n, la nitrito reductasa, que frecuentemente requiere ferredoxina como cofactor, convierte el nitrito en amon&#237;aco, el cual puede ser directamente asimilado en los componentes celulares. El proceso se desarrolla en las siguientes etapas:
<ul>
<li>Captaci&#243;n de nitrato: el nitrato es transportado al interior celular mediante transportadores espec&#237;ficos de membrana.</li>
<li>Reducci&#243;n de nitrato: la nitrato reductasa reduce el NO_3^- a NO_2^- utilizando electrones procedentes de NADH o FAD.</li>
<li>Reducci&#243;n de nitrito: la nitrito reductasa, con ferredoxina como cofactor, reduce el NO_2^- a NH_3, haciendo disponible el nitr&#243;geno para el metabolismo celular.</li>
</ul>
A diferencia de la desnitrificaci&#243;n, que elimina el nitr&#243;geno biodisponible de los ecosistemas y desempe&#241;a un papel crucial en el mantenimiento del equilibrio nitrogenado mediante la conversi&#243;n de nitratos en formas gaseosas, la reducci&#243;n asimilatoria de nitrato se centra en la incorporaci&#243;n de nitr&#243;geno a mol&#233;culas org&#225;nicas, asegurando su retenci&#243;n intracelular. Este proceso se integra en el metabolismo celular al proporcionar amon&#237;aco para su posterior asimilaci&#243;n.
V&#237;as de asimilaci&#243;n del amon&#237;aco
El amon&#237;aco, ya sea captado directamente o generado a trav&#233;s de la reducci&#243;n de nitrato, debe ser incorporado a mol&#233;culas org&#225;nicas para ser utilizado en el metabolismo celular. En funci&#243;n de la disponibilidad ambiental de amon&#237;aco, la asimilaci&#243;n se produce por medio de dos v&#237;as principales.
V&#237;a de aminaci&#243;n reductiva
Cuando las concentraciones de amon&#237;aco son elevadas, bacterias y hongos emplean preferentemente la v&#237;a de aminaci&#243;n reductiva. En este proceso:
<ul>
<li>Formaci&#243;n de &#945;-cetoglutarato: se sintetiza &#945;-cetoglutarato, un intermediario clave del ciclo del &#225;cido tricarbox&#237;lico (TCA).</li>
<li>S&#237;ntesis de Glutamato: la enzima glutamato deshidrogenasa (GDH) cataliza la conversi&#243;n de &#945;-cetoglutarato en glutamato incorporando amon&#237;aco y utilizando NAD(P)H como agente reductor.</li>
</ul>
Esta v&#237;a garantiza una r&#225;pida incorporaci&#243;n del amon&#237;aco cuando el nitr&#243;geno es abundante.
Sistema glutamina sintetasa&#8211;glutamato sintasa (GS-GOGAT)
En condiciones de baja disponibilidad de amon&#237;aco, los microorganismos emplean la v&#237;a GS-GOGAT, que es m&#225;s costosa en t&#233;rminos energ&#233;ticos, pero altamente eficiente para la asimilaci&#243;n de nitr&#243;geno. Este sistema consta de las siguientes etapas:
<ul>
<li>Formaci&#243;n de glutamina: la glutamina sintetasa (GS) cataliza la reacci&#243;n entre amon&#237;aco y glutamato para formar glutamina en una reacci&#243;n dependiente de ATP.</li>
<li>S&#237;ntesis de glutamato: la glutamato sintasa (GOGAT) convierte la glutamina en dos mol&#233;culas de glutamato, utilizando NADPH como agente reductor.</li>
<li>Redistribuci&#243;n del Nitr&#243;geno: el glutamato producido act&#250;a como donador de nitr&#243;geno en rutas biosint&#233;ticas, asegurando una asimilaci&#243;n y utilizaci&#243;n eficiente del nitr&#243;geno en procesos metab&#243;licos como la s&#237;ntesis de amino&#225;cidos y nucle&#243;tidos.</li>
</ul>
Fijaci&#243;n del nitr&#243;geno y su papel en el ciclo del nitr&#243;geno
A diferencia de la asimilaci&#243;n del nitr&#243;geno, la fijaci&#243;n del nitr&#243;geno es un proceso independiente presente exclusivamente en ciertos procariotas, como bacterias y arqueas diazotr&#243;ficas. Este proceso implica la reducci&#243;n enzim&#225;tica del nitr&#243;geno atmosf&#233;rico (N_2) a amon&#237;aco biodisponible mediante el complejo enzim&#225;tico nitrogenasa. La actividad de la nitrogenasa requiere ATP y electrones, lo que convierte esta v&#237;a en un proceso intensivo en energ&#237;a. La fijaci&#243;n del nitr&#243;geno desempe&#241;a un papel esencial en el ciclo global del nitr&#243;geno al reponer el nitr&#243;geno utilizable biol&#243;gicamente en ecosistemas, especialmente en entornos con deficiencia de nitr&#243;geno.
Conclusi&#243;n
La asimilaci&#243;n del nitr&#243;geno mediante la reducci&#243;n del nitrato y la incorporaci&#243;n de amon&#237;aco es fundamental para la supervivencia microbiana y el funcionamiento de los ecosistemas. La integraci&#243;n de estas rutas con redes metab&#243;licas centrales como el ciclo del TCA y la bios&#237;ntesis de amino&#225;cidos garantiza que el nitr&#243;geno se incorpore eficazmente al metabolismo celular. Estos procesos, en conjunto, sostienen el crecimiento microbiano y contribuyen al equilibrio global del nitr&#243;geno.

Asimilación de nitrógeno inorgánico

El nitr&#243;geno es un elemento esencial en los sistemas biol&#243;gicos, constituyendo un componente fundamental de las prote&#237;nas, los &#225;cidos ...

Education

Educación

JoVE Core

Microbiology

Microbiología

Unit

Unidad

Microbial Metabolism

Metabolismo microbiano

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

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...

redox reactions

Electron Carriers in Redox Metabolism

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introduction to metabolism

Metabolism: Energy Use and Biomolecule Synthesis

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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

Cellular Respiration: ATP Production Pathways

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electron transport chain components

Electron Transport Chain and ATP Production

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chemiosmosis and atp synthesis

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

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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

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amino acid biosynthetic pathways

Amino Acid Building from Cell Metabolites

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biosynthesis of nucleic acids

Nucleotide Building Blocks for DNA and RNA

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biosynthesis of lipids

How Membrane Lipids Vary Across Life

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formation of lipopolysaccharides

Lipopolysaccharides and Gram-Negative Defense

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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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