Q.28 Product of dissimilatory nitrate reduction is
- Ammonia
- Nitrogen
- Nitrate
- Nitric oxide
Dissimilatory nitrate reduction produces ammonia as its end product. This process, known as DNRA, uses nitrate as an electron acceptor in anaerobic respiration, retaining nitrogen in ecosystems.
Question Breakdown
The multiple-choice query asks for the product of dissimilatory nitrate reduction, with options: Ammonia, Nitrogen, Nitrate, Nitric oxide.
Option Analysis
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Ammonia: Correct. Dissimilatory nitrate reduction to ammonium (DNRA) reduces nitrate (NO₃⁻) to nitrite (NO₂⁻), then to NH₄⁺ via enzymes like nitrate reductase and nitrite reductase. This generates energy for microbes without nitrogen loss to gases.
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Nitrogen: Incorrect. This refers to dinitrogen gas (N₂) from denitrification, a separate process reducing nitrate through NO, N₂O to N₂, which releases nitrogen from ecosystems.
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Nitrate: Incorrect. Nitrate is the starting substrate, not the product; it gets reduced further in dissimilatory pathways.
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Nitric oxide: Incorrect. Nitric oxide (NO) is an intermediate in denitrification or sometimes DNRA side reactions, but not the main end product.
Introduction to Dissimilatory Nitrate Reduction
In microbial metabolism, the dissimilatory nitrate reduction product is ammonia, a key process called DNRA that conserves nitrogen in soils and sediments. Unlike denitrification, DNRA retains bioavailable NH₄⁺ for ecosystems. This anaerobic respiration uses nitrate (NO₃⁻) as an electron acceptor.
How DNRA Works
Nitrate reduces to nitrite via nitrate reductase, then to ammonia by nitrite reductase (e.g., Nrf enzyme). The reaction is: NO₃⁻ + 8e⁻ + 10H⁺ → NH₄⁺ + 3H₂O. Bacteria like Pseudomonas thrive in carbon-rich, low-oxygen environments.
Factors boosting DNRA include high C/N ratios (e.g., 8:1), neutral-alkaline pH (7-10), and temperatures around 30°C.
DNRA vs Denitrification
Process End Product Ecological Impact Key Microbes DNRA (Dissimilatory Nitrate Reduction) Ammonia (NH₄⁺) Nitrogen retention Pseudomonas, Acididesulfobacillus Denitrification Nitrogen gas (N₂) Nitrogen loss Paracoccus, Pseudomonas DNRA dominates in organic-rich sediments; denitrification in low-carbon settings.
Ecological Importance
DNRA prevents nitrogen loss in agriculture and wastewater, aiding nutrient recycling. It counters denitrification’s greenhouse gas emissions (N₂O). Recent studies highlight novel DNRA enzymes handling nitric oxide stress.
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