Microbial growth phases: How is the stationary phase of a batch culture best described in terms of cell population behavior after reaching the maximum level?

Introduction:
Batch culture growth curves follow lag, exponential, deceleration, stationary, and death phases. Correctly characterizing the stationary phase is essential for interpreting product formation patterns and planning harvests.

Given Data / Assumptions:

• Closed system with finite nutrients and accumulation of products.
• Population has already passed through exponential and deceleration phases.
• Observation focuses on changes in viable cell counts over time.

Concept / Approach:
Stationary phase is defined by a balance between cell divisions and cell deaths such that there is no net increase in total viable count. Nutrients may be limiting, inhibitory metabolites may accumulate, and maintenance energy demands dominate.

Step-by-Step Solution:
Track viable counts versus time and identify the plateau region.Relate the plateau to zero net growth: divisions approximately equal deaths.Connect to physiology: stress responses, secondary metabolism, and spore formation in some species.

Verification / Alternative check:
Dry cell weight may remain roughly constant while specific activity of secondary metabolites can change, confirming a stationary state in cell numbers rather than metabolic stasis.

Why Other Options Are Wrong:
Deceleration after maximum growth rate: describes the transition phase, not stationary.

Acceleration after maximum: contradicts resource limitation.

Deceleration after minimum: does not match any standard batch phase definition.

Common Pitfalls:

• Confusing stationary with death phase; in death phase, viable counts decline.
• Assuming metabolism stops; many biosyntheses persist in stationary conditions.

Final Answer:
No further net increase in cell population after a maximum value is reached