Section 4: Bioprocess Engineering and Process Biotechnology
Mass transfer in bioprocesses (kLa)
Subtopic: Fundamentals of Mass transfer in bioprocesses (kLa)
Question Statement:
Which of the following factors can influence the lag phase of a microbial culture in a batch
fermentor?
P. Inoculum size
Q. Inoculum age
R. Medium composition
Options:
(A) P and Q only
(B) Q and R only
(C) P and R only
(D) P, Q and R
Official Answer Key:
D
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2019 Q.50)**
**1. Governing Concept**:
- **Topic**: Microbial Fermentation Kinetics & Lag Phase Duration
- Factors that determine the length of the microbial **lag phase** upon inoculating a batch fermenter:
1. **Physiological state and age of inoculum**: Cells harvested from exponential phase have active translational machinery and minimal lag; cells from stationary or starved phases require prolonged metabolic adaptation.
2. **Inoculum size / density**: Larger inoculum sizes dilute toxic medium components and reach quorum more rapidly, reducing lag time.
3. **Composition of pre-culture vs. production medium**: Inoculating cells from a complex medium into a minimal or novel carbon source medium requires de novo synthesis of inducible catabolic operons, significantly extending the lag phase.
4. **Temperature and pH changes**: Temperature shifts necessitate cold/heat-shock chaperone adaptation.
**2. Option Analysis**:
- **Option (A) is INCORRECT**: Incomplete factor list.
- **Option (B) is INCORRECT**: Incomplete list.
- **Option (C) is INCORRECT**: Incomplete list.
- **Option (D) is CORRECT**: All enumerated physiological, chemical, and physical factors collectively influence lag phase duration.
**3. Final Answer**:
- **Correct Choice**: **D**
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