Laboratory Evolution to Alternating Substrate Environments Yields Distinct Phenotypic and Genetic Adaptive Strategies

Area of Science:

• Microbial evolution
• Systems biology
• Metabolic engineering

Background:

• Adaptive laboratory evolution (ALE) typically uses static environments, yet natural and bioprocessing settings involve dynamic nutrient conditions.
• Understanding adaptation to fluctuating environments is crucial for both fundamental evolutionary biology and applied biotechnology.

Purpose of the Study:

• To investigate the adaptive strategies and genetic mechanisms of *Escherichia coli* evolving under alternating carbon substrates (glucose with xylose, glycerol, or acetate).
• To explore the emergence of generalist versus specialist strains and their phenotypic differences in response to dynamic culturing.

Main Methods:

• Evolving *Escherichia coli* batch cultures through serial propagation in alternating carbon substrate environments.
• Utilizing genome sequencing, gene expression analysis, and genome-scale metabolic modeling to characterize evolved strains.

Main Results:

• Identified specific genetic changes selected under dynamic conditions, leading to diverse adaptation strategies.
• Observed the development of persistent generalist strains or alternating specialist subpopulations, with varying diauxic lag phenotypes.
• Gene expression data and metabolic modeling elucidated distinct transcriptional and metabolic strategies for growth optimization.

Conclusions:

• Dynamic nutrient environments drive unique evolutionary trajectories and adaptation mechanisms in microbial populations.
• ALE in fluctuating conditions can generate strains with altered metabolic and genetic profiles, potentially useful for industrial bioprocessing.
• This study provides a framework for understanding microbial adaptation to complex environments and optimizing experimental designs for evolutionary studies.