Question

In a batch culture of Penicillium chrysogenum, the maximum penicillin synthesis occurs during the

• A. Lag phase
• B. Stationary phase
• C. Exponential phase
• D. Death phase

Hint:

To maximize the yield of secondary metabolites like penicillin in industrial fermentation, a fed-batch process is used to extend the stationary phase (idiophase) by feeding nutrients at a controlled rate that prevents rapid cell growth.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
In industrial bioprocesses, microbial products are classified into two main categories based on the relationship between cell growth and product synthesis:
Primary metabolites, which are produced during the active growth phase (trophophase) and are essential for cell survival.
Secondary metabolites, which are produced after active growth slows down (idiophase) and are not required for normal cell growth.

Step 2: Detailed Explanation:
Penicillin, produced by the filamentous fungus Penicillium chrysogenum, is a classic secondary metabolite.
During the lag and exponential phases (trophophase), the fungus uses its carbon and nitrogen sources to build biomass and support rapid cell division.
During this active growth phase, little to no penicillin is synthesized.
As nutrients become depleted and toxic products accumulate, the culture enters the stationary phase (idiophase), where the net growth rate drops to near zero.
During this stationary phase, the cells undergo metabolic changes and begin synthesizing secondary metabolites like penicillin.
Penicillin is synthesized from three amino acid precursors (L-aminoadipic acid, L-cysteine, and L-valine) through a pathway regulated by nutrient levels.
High levels of carbon (glucose) and nitrogen suppress the expression of the penicillin biosynthetic genes during the growth phase.
When these nutrients are depleted during the stationary phase, this repression is lifted, initiating penicillin synthesis.
Therefore, the maximum rate of penicillin production occurs during the stationary phase of a batch culture.

Step 3: Final Answer:
In Penicillium chrysogenum cultures, the maximum synthesis of penicillin occurs during the stationary phase.