Practice question

MCQ

Question

The nitrogen fixing bacterium, Rhizobium /eguminosarum, isolated from the root nodules of garden pea (Pisum sativum) is cultured in a petri plate containing appropriate nutrient agar medium. A bacterial colony was picked and inoculated into a liquid growth medium to scale up the culture for the production of biofertilizer. Which one of the following statements is correct?

Options

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The liquid culture will be red/pink in color due to the accumulation of the pigment leghaemoglobin. The rhizobial cells when reinoculated into the rhizosphere of soybean plants will effectively nodulate its roots to fix atmospheric nitrogen. The rhizobial cells cannot fix nitrogen when exposed to atmospheric air. Correct The rhizobial cells get transformed into bacterioids when grown in liquid media.

Explanation

Rhizobium nitrogenase is extremely O₂-sensitive, so free-living aerobic culture cannot fix N₂. Leghemoglobin, bacteroid differentiation and host-specific nodulation occur only inside legume nodules. Pea isolate fails to nodulate soybean, liquid culture is not pink.

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