During growth of Penicillium chrysogenum, in which production phase is maximal penicillin biosynthesis typically observed?

Introduction / Context:
Penicillin is a classic secondary metabolite. Its biosynthesis peaks after rapid biomass accumulation, when growth rate drops and metabolism shifts to secondary pathways under controlled nutrient limitation in a fed-batch process.

Given Data / Assumptions:

• Organism: Penicillium chrysogenum.
• Process: aerobic fed-batch; controlled carbon/nitrogen feeds.
• Phases: trophophase (growth), idiophase (production), decline.

Concept / Approach:
Secondary metabolite production typically coincides with idiophase, not with maximum specific growth rate. Process control aims to reach and hold the culture in this regime where penicillin gene clusters are upregulated and precursors are effectively channeled to product.

Step-by-Step Solution:

Verification / Alternative check:
Historical penicillin process data show low titers during exponential growth with a strong rise post-exponential.

Why Other Options Are Wrong:

• First phase: primarily biomass formation.
• Third phase: cells lose viability; productivity drops.
• Same in all phases: contradicts secondary metabolism behavior.

Common Pitfalls:
Equating high cell density with high product formation; timing matters for secondary metabolites.

Final Answer:
During the second phase (idiophase, slowed growth)