Catabolite Utilization Patterns — What does diauxie describe in microbial growth on multiple substrates?

Introduction:
Diauxic growth is a classic phenomenon observed when microbes encounter two carbon sources, one preferred. The growth curve shows two distinct exponential phases separated by a lag as the cells adjust metabolic regulation. Recognizing this pattern is foundational for understanding catabolite repression and metabolic regulation.

Given Data / Assumptions:

• Two utilizable substrates are present, one preferred over the other.
• Regulatory systems control enzyme synthesis for catabolic pathways.
• Culture conditions allow observation of growth phases over time.

Concept / Approach:

In diauxie, cells first consume the preferred substrate, typically leading to rapid growth. Upon its depletion, there is a lag while the cells induce enzymes needed to catabolize the secondary substrate. Then a second growth phase begins. This sequential use is driven by regulatory mechanisms such as catabolite repression and inducer exclusion.

Step-by-Step Solution:

Verification / Alternative check:

Classical glucose–lactose experiments in Escherichia coli show diauxic patterns with initial glucose consumption followed by induction of the lac operon and a second growth phase on lactose.

Why Other Options Are Wrong:

A describes nutrient requirements, not the pattern. B is the death phase, not diauxie. C is co-utilization, not sequential use. E is extreme inhibition, not the regulatory switch between phases.

Common Pitfalls:

Assuming all multi-substrate cultures show simultaneous uptake; regulatory hierarchies frequently enforce priority use.

Final Answer:

Stagewise (sequential) uptake of substrates, producing two growth phases