Q.71 Secondary metabolites such as penicillin from mold are produced during the _______ .
(A) lag phase (B) idiophase (C) log phase (D) decline phase

The correct answer is (B) idiophase.​

Penicillin, a secondary metabolite from Penicillium mold, forms specifically during idiophase, the production phase after rapid growth slows due to nutrient limits. This phase aligns with secondary metabolism in fungal fermentations, distinct from standard bacterial growth curves.​

Option Analysis

(A) Lag phase: Cells adapt to new conditions without dividing or producing secondary metabolites like penicillin; focus remains on enzyme synthesis and repair.​

(B) Idiophase: Correct choice—secondary metabolites such as penicillin peak here as growth ceases (post-trophophase), with reduced carbohydrates favoring antibiotic synthesis over 5-7 days in Penicillium cultures.​

(C) Log phase: Rapid cell division occurs with primary metabolite production for growth; secondary metabolites like penicillin are minimal or absent.​

(D) Decline phase: Cell death dominates due to toxin buildup and starvation; no active secondary metabolite production happens.​

Secondary metabolites such as penicillin from mold are produced during the idiophase, a critical stage in microbial fermentation vital for biotechnology and CSIR NET life sciences. This phase follows trophophase (growth) and enables antibiotics like penicillin from Penicillium chrysogenum when nutrients limit cell division.​

Key Phases in Metabolite Production

Microbial batch cultures show four main growth phases, but secondary metabolites like penicillin tie to idiophase within stationary-like conditions.​

• Lag phase: Adaptation; no division or penicillin output.​

• Log (exponential) phase: Fast growth, primary metabolites only.​

• Idiophase (secondary production): Nutrient depletion triggers penicillin synthesis via specialized pathways.​

• Decline phase: Lysis; production stops.​

Penicillin Production Process

Penicillium fermentation splits into trophophase (mycelial growth, ~30 hours) and idiophase (penicillin peaks days 2-7, pH rises to 8). Fed-batch methods optimize this for industrial yields, using precursors like phenylacetic acid.​

Idiophase mastery aids CSIR NET questions on biotechnology and microbial physiology.