Section 4: Bioprocess Engineering and Process Biotechnology
Mass transfer in bioprocesses (kLa)
Subtopic: Fundamentals of Mass transfer in bioprocesses (kLa)
Question Statement:
Which one of the following is catabolized during endogenous metabolism in a batch
bacterial cultivation?
Options:
(A) internal reserves
(B) extracellular substrates
(C) extracellular products
(D) toxic substrates
Official Answer Key:
A
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2019 Q.27)**
**1. Governing Concept**:
- **Topic**: Microbiology & Endospore Germination Physiology
- During bacterial endospore formation (*Bacillus*, *Clostridium*), heat and desiccation resistance is conferred by accumulation of **Dipicolinic acid (pyridine-2,6-dicarboxylic acid, DPA)** complexed with calcium ions ($\text{Ca}^{2+}\text{-DPA}$, constituting up to $10-15\%$ of dry spore weight) in the spore core.
- In addition, **Small Acid-Soluble Spore Proteins (SASPs)** bind and protect spore DNA.
- During spore germination and outgrowth:
- Spore dipicolinate ($\text{Ca}^{2+}\text{-DPA}$) is rapidly released and excreted.
- SASPs are rapidly cleaved and **catabolized by specialized germination proteases (GPR)** to provide a rich amino acid pool and carbon/energy source for initial protein synthesis.
**2. Option Analysis**:
- **Option (A) [SASPs / Spore proteins] is CORRECT**: Degradation of small acid-soluble spore proteins provides essential metabolic amino acids during early germination.
- **Option (B) is INCORRECT**: Peptidoglycan cortex is enzymatically lysed, not primarily catabolized for energy.
- **Option (C) is INCORRECT**: Keratin-like spore coat proteins are shed, not catabolized.
- **Option (D) is INCORRECT**: Dipicolinic acid is excreted into the medium, not catabolized.
**3. Final Answer**:
- **Correct Choice**: **A**
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