Question

Which of the following is not a phosphate solubilizing microorganism?

• A. Bacillus sp.
• B. Penicillium sp.
• C. Aspergillus sp.
• D. Frankia sp.

Hint:

Frankia = Nitrogen (Non-legumes).
Bacillus/Aspergillus = Phosphorus (Solubilizers).

Answer 1

The Correct Option is D

Concept: Phosphate Solubilizing Microorganisms (PSMs) are beneficial microbes capable of solubilizing inorganic phosphorus from insoluble sources (like rock phosphate) into a soluble form ($H_2PO_4^-$ or $HPO_4^{2-}$) that plants can absorb.

Step 1: Identifying Common PSMs.
Many soil bacteria and fungi produce organic acids that lower the soil pH and dissolve phosphate. Common examples include:
• Bacteria: Bacillus and Pseudomonas.
• Fungi: Aspergillus and Penicillium.

Step 2: Analyzing Frankia.
{Frankia is a genus of actinomycetes known for its ability to form symbiotic nitrogen-fixing nodules on the roots of non-leguminous plants (actinorhizal plants like Alnus). Its primary biological role is nitrogen fixation ($N_2 \rightarrow NH_3$), not the solubilization of mineral phosphorus.

Step 3: Conclusion.
Since Frankia is specialized for nitrogen fixation and the others are well-documented PSMs, option (4) is the correct outlier.