Question

All of the following statements concerning the Actinomycetes filamentous soil bacterium are correct, except that Frankia

• A. Can induce root nodules on many plant species.
• B. Can fix nitrogen in the free-living state.
• C. Cannot fix specialized vesicles in which the nitrogenase is protected from oxygen by a chemical barrier involving triterpene hopanoids.
• D. Like Rhizobium, it usually infects its host plant through root hair deformation and stimulates cell proliferation in the host's cortex.

Answer 1

The correct option is B Can fix nitrogen in the free-living state.

Frankia is a genus of filamentous, nitrogen-fixing bacterium and it forms a symbiotic relationship with many plants. It causes root hair deformation in a way that it enters the cortical cells and induces the nodule formations, which look like those induced by Rhizobium in legumes. It produces three cell types: sporangiospores, hyphae, and diazo-vesicles. The diazo-vesicles are responsible for the supplying of sufficient nitrogen to the host plant during symbiosis. Reductive nitrogen fixation takes place in the diazo-vesicles and this process is protected from molecular oxygen by many layers of tightly stacked hopanoid lipids. It converts atmospheric N${}_2$ gas into ammonia.

Thus, the correct answer is option B.