Question:
Which of the following is a symbiotic nitrogen fixer?
Which of the following is a symbiotic nitrogen fixer?
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The genus Ensifer includes several fast-growing species of rhizobia that form nitrogen-fixing nodules on legumes.
Updated On: Jul 13, 2026
- Ensifer fredii
- Acetobacter diazotrophicus
- Azospirillum lipoferrum
- Pseudomonas marginalis
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The Correct Option is A
Solution and Explanation
Step 1: Understanding the Concept:
Biological nitrogen fixation (BNF) is performed by specific prokaryotes (diazotrophs) that can be free-living, associative, endophytic, or symbiotic.
Step 2: Detailed Explanation:
- Ensifer fredii (formerly known as Sinorhizobium fredii) is a fast-growing, soil-dwelling rhizobial bacterium.
It establishes a true mutualistic symbiosis with leguminous plants (specifically soybeans, Glycine max, and cowpeas), forming nodules on their roots where it fixes atmospheric nitrogen.
- Acetobacter diazotrophicus is an acid-tolerant endophytic diazotroph associated with sugarcane tissues, but it does not form symbiotic nodules.
- Azospirillum lipoferum is an associative nitrogen-fixing bacterium that lives on root surfaces.
- Pseudomonas marginalis is a plant-associated bacterium but is not a nitrogen fixer.
Step 3: Final Answer:
Hence, Ensifer fredii is a symbiotic nitrogen fixer.
Biological nitrogen fixation (BNF) is performed by specific prokaryotes (diazotrophs) that can be free-living, associative, endophytic, or symbiotic.
Step 2: Detailed Explanation:
- Ensifer fredii (formerly known as Sinorhizobium fredii) is a fast-growing, soil-dwelling rhizobial bacterium.
It establishes a true mutualistic symbiosis with leguminous plants (specifically soybeans, Glycine max, and cowpeas), forming nodules on their roots where it fixes atmospheric nitrogen.
- Acetobacter diazotrophicus is an acid-tolerant endophytic diazotroph associated with sugarcane tissues, but it does not form symbiotic nodules.
- Azospirillum lipoferum is an associative nitrogen-fixing bacterium that lives on root surfaces.
- Pseudomonas marginalis is a plant-associated bacterium but is not a nitrogen fixer.
Step 3: Final Answer:
Hence, Ensifer fredii is a symbiotic nitrogen fixer.
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