Microbial population dynamics decouple growth response from environmental nutrient concentration

Area of Science:

• Microbiology
• Evolutionary Biology
• Ecological Modeling

Background:

• Microbial growth rates are fundamentally linked to nutrient availability.
• The Monod model describes this relationship using maximum growth rate and half-saturation concentration.
• Understanding half-saturation concentration variability is crucial for predicting microbial responses.

Purpose of the Study:

• To investigate the factors driving the wide variation in microbial half-saturation concentrations.
• To develop an evolutionary model explaining how population dynamics affect adaptation of these concentrations.
• To determine if evolved half-saturation concentrations accurately reflect environmental resource levels.

Main Methods:

• Surveyed microbial growth response data across diverse organisms and resources.
• Developed an evolutionary model incorporating demographic fluctuations (genetic drift).
• Analyzed the impact of different population dynamics (bottlenecks vs. dilutions) on adaptation.

Main Results:

• Half-saturation concentrations exhibit orders-of-magnitude variation, even for the same organism/resource.
• Demographic fluctuations constrain the adaptation of half-saturation concentrations.
• Periodic bottlenecks lead to adaptation proportional to resource concentration, while dilutions decouple adaptation.

Conclusions:

• Population dynamics critically shape microbial ecological traits like half-saturation concentrations.
• Evolved half-saturation concentrations may not always reflect the organism's environment.
• This explains how microbes in rich environments can still adapt to low resource growth.