Microbial Growth Curves — Stationary Phase: What is the relationship between the specific growth rate and the specific death rate during the stationary phase of a batch culture?

Introduction:
Microbial batch cultures exhibit distinct phases: lag, exponential, stationary, and death. The stationary phase is a dynamic equilibrium, not a complete halt in metabolism. Understanding what balances during stationary phase is essential for interpreting biomass data and product formation patterns in bioprocesses.

Given Data / Assumptions:

• Closed batch system with limited nutrients and potential waste accumulation.
• Biomass concentration becomes approximately constant in stationary phase.
• Cells may still divide, and others may die at comparable rates.

Concept / Approach:

When the net change in cell number is near zero, the time derivative of biomass is approximately zero. This occurs when the specific growth rate and specific death rate balance. The culture appears steady in terms of total viable counts or optical density, even though underlying processes continue.

Step-by-Step Solution:

Verification / Alternative check:

Empirical measurements of viable counts, coupled with lysis and turnover assessments, often show small oscillations around a near-constant biomass. This supports the conceptual balance between formation of new cells and loss of others.

Why Other Options Are Wrong:

A: Proportional but unequal does not yield zero net growth. C and E: Inequality would cause net decline or increase, contradicting stationary behavior. D: There is a clear relationship; equality of rates explains the constant biomass.

Common Pitfalls:

Believing stationary phase is complete metabolic inactivity. In reality, maintenance metabolism, secondary metabolite formation, and stress responses are active.

Final Answer:

Growth rate is equal to death rate