- Microorganisms having nitrilase activity can be enriched from soil samples by supplying nitriles as the sole nitrogen or carbon source in the growth medium. A problem with this approach is that false-positive strains may be isolated, which use nitrites to produce amide with the help of a different enzyme activity such as
(1) phosphorylases (2) phosphatases
(3) hydratases (4) phosphoestarasesConcept behind the question
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True nitrilases hydrolyze nitriles directly to the corresponding acid + ammonia.
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Some microbes instead use a nitrile hydratase → amidase pathway, where nitrile is first hydrated to an amide, which is then hydrolyzed.
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During enrichment on nitriles, such organisms can grow and appear “positive,” even though they lack nitrilase; the misleading step is catalyzed by a hydratase.
Thus, the enzyme class responsible for this false‑positive growth is a hydratase.
Option-wise explanation
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Phosphorylases
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Catalyze the addition of inorganic phosphate to glycosidic or other bonds (e.g., glycogen phosphorylase).
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They are not involved in converting nitriles to amides, so they cannot explain the false positives.
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Phosphatases
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Remove phosphate groups from phosphorylated molecules.
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Again, no role in nitrile → amide conversion; irrelevant to this enrichment problem.
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Hydratases – correct
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Hydratases add water across a multiple bond (e.g., C≡N, C=C).
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In nitrile metabolism, nitrile hydratase converts a nitrile to its corresponding amide.
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Microbes carrying a nitrile‑hydratase/amidase system can utilize nitriles yet do not have nitrilase, giving false‑positive strains in a nitrilase screen.
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Phosphoesterases
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Hydrolyze phosphoester bonds (e.g., in nucleotides or phospholipids).
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Not involved in nitrile hydration or amide formation, so they are not responsible for the observed false positives.
Therefore, the enzyme activity that leads to false positives in nitrilase enrichment from soil is hydratase activity (option 3).
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