all of the following statements concerning the actinomycetes filamentous soil bacterium are correct except that Frankia

Options

A. A. Can induce root nodules on many plant species
B. B. Can fix nitrogen in the free-living state
C. C. Like Rhizobium, it usually infects its host plant through root hair deformation and stimulates cell proliferation on the hosts' cortex
D. D. Forms specialised vesicles, in which the nitrogenase is protected from oxygen by a chemical barrier involving triterpene hopanoids

Answer

To solve the question regarding the statements about the actinomycetes filamentous soil bacterium Frankia, we will analyze each statement one by one to determine which one is incorrect.

### Step-by-Step Solution:

1. **Understanding Frankia**:
- Frankia is a genus of filamentous bacteria known for its nitrogen-fixing ability. It forms symbiotic relationships with various plants, particularly non-leguminous plants.

**Hint**: Remember that Frankia is a nitrogen-fixing bacterium that forms symbiotic relationships with plants.

2. **Analyzing Statement A**:
- "Frankia can induce root nodules on many plant species."
- This statement is correct. Frankia induces root nodules similar to those formed by Rhizobium in legumes.

**Hint**: Think about the role of Frankia in plant symbiosis and nodule formation.

3. **Analyzing Statement B**:
- "Frankia can fix nitrogen in the free living state."
- This statement is incorrect. Frankia primarily fixes nitrogen in a symbiotic state within the nodules of host plants, not in a free-living state.

**Hint**: Consider the conditions under which Frankia is known to fix nitrogen.

4. **Analyzing Statement C**:
- "Like Rhizobium, it usually infects its host plant through root hair deformation and stimulates cell proliferation on the host cortex."
- This statement is correct. Frankia does infect host plants similarly to Rhizobium, causing root hair deformation.

**Hint**: Compare the infection methods of Frankia and Rhizobium.

5. **Analyzing Statement D**:
- "Form specialized vessels in which the nitrogenase is protected from oxygen by a chemical barrier involving triterpene hapenoids."
- This statement is correct. Frankia forms specialized structures called diazovessels that protect nitrogenase from oxygen.

**Hint**: Recall the structural adaptations of Frankia that facilitate nitrogen fixation.

6. **Conclusion**:
- The only incorrect statement is option B: "Frankia can fix nitrogen in the free living state." Therefore, this is the answer to the question.

### Final Answer:
The statement that is incorrect concerning the actinomycetes filamentous soil bacterium Frankia is: **B. can fix nitrogen in the free living state.**