Question

Given below are two statements, one is labeled as Assertion (A) and the other one is labeled as Reason (R).
Assertion (A) : Bacillus megaterium is an efficient P-solubilizing bacteria.
Reason (R) : Bacillus megaterium produces different organic acids for dissolution.
In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Applying PSB biofertilizers like *Bacillus megaterium* can significantly improve fertilizer use efficiency, allowing farmers to reduce the application rates of expensive chemical phosphorus fertilizers.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Phosphate-solubilizing bacteria (PSB) are beneficial soil microorganisms capable of solubilizing insoluble inorganic phosphorus compounds into plant-available orthophosphate forms.

Step 3: Detailed Explanation:
Let us evaluate both statements:
- Assertion (A): *Bacillus megaterium* (specifically *Bacillus megaterium* var. *phosphaticum*) is widely used as a biofertilizer because it is a highly efficient phosphate-solubilizing bacterium.
It releases bound phosphorus from insoluble sources (such as tricalcium phosphate, rock phosphate, and iron/aluminum phosphates) in the soil.
Therefore, Assertion (A) is correct.
- Reason (R): The primary mechanism by which *Bacillus megaterium* solubilizes insoluble inorganic phosphorus is through the biosynthesis and secretion of organic acids (such as citric, lactic, gluconic, and succinic acids).
These organic acids lower the surrounding soil pH, causing the insoluble phosphate compounds to dissolve.
Additionally, the organic acid anions can chelate the metal cations (like $\text{Ca}^{2+}$, $\text{Fe}^{3+}$, and $\text{Al}^{3+}$) bound to the phosphate, releasing free orthophosphate ions into the soil solution.
Therefore, Reason (R) is correct and directly explains the mechanism behind Assertion (A).
Both statements are true, and (R) is the correct explanation of (A).

Step 4: Final Answer:
Both (A) and (R) are true, and (R) is the correct explanation of (A), corresponding to option (A).