Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : In Bacillus culture raised in a chemically defined medium, sporulation is initiated in the stationary phase.
Reason (R) : Lack of nutrients and high cell density trigger sporulation.
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 and (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:

Bacterial endospores are highly resistant to heat, desiccation, radiation, and disinfectants, primarily due to the presence of calcium dipicolinate in the spore core and a thick protein coat.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Sporulation is the process of producing highly resistant, dormant endospores.
This survival mechanism is utilized by certain Gram-positive bacteria, particularly *Bacillus* and *Clostridium* species, when they encounter harsh environmental conditions.

Step 2: Detailed Explanation:
Let us analyze both statements:
- Assertion (A): In a batch culture of *Bacillus* grown in a chemically defined medium, cells grow exponentially during the log phase.
As the population enters the stationary phase, cell division slows down, and the cells initiate the complex morphological process of sporulation.
Thus, Assertion (A) is true.
- Reason (R): Sporulation is a highly energy-intensive process that is initiated only when necessary.
The primary triggers that initiate sporulation are:
1. Nutrient Starvation: Depletion of essential carbon, nitrogen, or phosphorus sources in the growth medium during the stationary phase.
2. High Cell Density: Sensed through the accumulation of extracellular quorum-sensing signaling peptides.
These dual signals trigger a regulatory cascade (starting with the phosphorylation of Spo0A) that activates the transcription of *spo* genes, starting sporulation.
Therefore, Reason (R) is true and directly explains the environmental and population conditions (A) that trigger sporulation.

Step 3: Final Answer:
Both (A) and (R) are true, and (R) is the correct explanation of (A), corresponding to option (A).